Merge pull request #1169 from Hestia-Homes/feature/per-cert-mapper-validation

Feature/per cert mapper validation

backend/documents_parser/elmhurst_extractor.py

@@ -269,8 +269,8 @@ class ElmhurstSiteNotesExtractor:
         )
 
     def _wall_details_from_lines(self, lines: List[str]) -> WallDetails:
-        thickness_raw = self._local_val(lines, "Wall Thickness")
-        thickness_mm = (
+        thickness_raw: Optional[str] = self._local_val(lines, "Wall Thickness")
+        thickness_mm: Optional[int] = (
             int(thickness_raw.split()[0]) if thickness_raw else None
         )
         # Composite / retrofit insulation thickness — Summary §7.0
@@ -280,12 +280,8 @@ class ElmhurstSiteNotesExtractor:
         # is local-scoped inside the §7 block so it does not collide
         # with the §8 Roofs / §9 Floors blocks. None when the PDF
         # omits the line (no retrofit lodged).
-        ins_thickness_raw = self._local_val(lines, "Insulation Thickness")
-        insulation_thickness_mm = (
-            int(ins_thickness_raw.split()[0])
-            if ins_thickness_raw and ins_thickness_raw.split()[0].isdigit()
-            else None
-        )
+        ins_thickness_raw: Optional[str] = self._local_val(lines, "Insulation Thickness")
+        insulation_thickness_mm: Optional[int] = self._parse_thickness_mm(ins_thickness_raw)
         return WallDetails(
             wall_type=self._local_str(lines, "Type"),
             insulation=self._local_str(lines, "Insulation"),
@@ -322,12 +318,10 @@ class ElmhurstSiteNotesExtractor:
                 continue
             if area <= 0:
                 continue
-            thickness_raw = self._local_val(lines, f"Alternative Wall {n} Thickness")
-            thickness_mm = (
-                int(thickness_raw.split()[0])
-                if thickness_raw and thickness_raw.split()[0].isdigit()
-                else None
+            thickness_raw: Optional[str] = self._local_val(
+                lines, f"Alternative Wall {n} Thickness"
             )
+            thickness_mm: Optional[int] = self._parse_thickness_mm(thickness_raw)
             result.append(AlternativeWall(
                 area_m2=area,
                 wall_type=self._local_str(lines, f"Alternative Wall {n} Type"),
@@ -356,11 +350,25 @@ class ElmhurstSiteNotesExtractor:
         lines = [l.strip() for l in main_body.splitlines() if l.strip()]
         return self._wall_details_from_lines(lines)
 
+    @staticmethod
+    def _parse_thickness_mm(raw: Optional[str]) -> Optional[int]:
+        """Parse an Elmhurst "Insulation Thickness" cell ("100 mm",
+        "400+ mm") to integer mm. The bucket-cap "400+ mm" (Table 17/18
+        max tabulated row) carries a trailing "+" that a bare
+        `.split()[0].isdigit()` test rejects — strip to the leading
+        digits so the cap parses through to the cascade with its numeric
+        value (simulated case 5: roof "400+ mm" was silently dropped →
+        u_roof fell back to the age-J default 0.16 instead of the
+        300mm+ value 0.11). Returns None when the cell is absent or
+        carries no leading number ("As Built", "N None")."""
+        if not raw:
+            return None
+        match = re.match(r"\d+", raw.strip())
+        return int(match.group()) if match else None
+
     def _roof_details_from_lines(self, lines: List[str]) -> RoofDetails:
-        thickness_raw = self._local_val(lines, "Insulation Thickness")
-        thickness_mm = (
-            int(thickness_raw.split()[0]) if thickness_raw and thickness_raw.split()[0].isdigit() else None
-        )
+        thickness_raw: Optional[str] = self._local_val(lines, "Insulation Thickness")
+        thickness_mm: Optional[int] = self._parse_thickness_mm(thickness_raw)
         insulation = self._local_str(lines, "Insulation")
         # The Summary PDF omits the "Insulation Thickness" line entirely
         # when no retrofit insulation is lodged (e.g. "Insulation: N None"
@@ -384,18 +392,14 @@ class ElmhurstSiteNotesExtractor:
         return self._roof_details_from_lines(lines)
 
     def _floor_details_from_lines(self, lines: List[str]) -> FloorDetails:
-        u_val_raw = self._local_val(lines, "Default U-value")
-        default_u = float(u_val_raw) if u_val_raw else None
+        u_val_raw: Optional[str] = self._local_val(lines, "Default U-value")
+        default_u: Optional[float] = float(u_val_raw) if u_val_raw else None
         # RdSAP 10 §5.13 Table 20 — retro-fitted upper floors lodge an
         # "Insulation Thickness: NNN mm" cell so the cascade can route
         # via the per-thickness column. Mirror of the §8 roof extractor
         # at `_roof_details_from_lines`.
-        thickness_raw = self._local_val(lines, "Insulation Thickness")
-        thickness_mm = (
-            int(thickness_raw.split()[0])
-            if thickness_raw and thickness_raw.split()[0].isdigit()
-            else None
-        )
+        thickness_raw: Optional[str] = self._local_val(lines, "Insulation Thickness")
+        thickness_mm: Optional[int] = self._parse_thickness_mm(thickness_raw)
         return FloorDetails(
             location=self._local_str(lines, "Location"),
             floor_type=self._local_str(lines, "Type"),
@@ -668,12 +672,24 @@ class ElmhurstSiteNotesExtractor:
                 # even when the main wall fields are inherited; merge
                 # them into the inherited WallDetails so the bp carries
                 # them through to its SapBuildingPart.
+                #
+                # "As Main Wall: Yes" inherits the EXTERNAL wall
+                # construction only — the PARTY WALL TYPE is lodged
+                # separately in the extension's §7 block and may differ
+                # (cert 001431: Main "CU Cavity masonry unfilled" U=0.5,
+                # 1st Extension "U Unable to determine" → RdSAP default
+                # U=0.25). Read the extension's own party wall type when
+                # present; fall back to the main's only when absent.
+                ext_party_wall_type = (
+                    self._local_str(wall_lines, "Party Wall Type")
+                    or main_walls.party_wall_type
+                )
                 walls = WallDetails(
                     wall_type=main_walls.wall_type,
                     insulation=main_walls.insulation,
                     thickness_unknown=main_walls.thickness_unknown,
                     u_value_known=main_walls.u_value_known,
-                    party_wall_type=main_walls.party_wall_type,
+                    party_wall_type=ext_party_wall_type,
                     thickness_mm=main_walls.thickness_mm,
                     insulation_thickness_mm=main_walls.insulation_thickness_mm,
                     alternative_walls=self._alternative_walls_from_lines(wall_lines),
@@ -799,6 +815,12 @@ class ElmhurstSiteNotesExtractor:
         "North", "South", "East", "West", "NE", "NW", "SE", "SW",
     })
     _BP_INLINE_TOKENS = frozenset({"Main"})  # "Extension" only appears as suffix
+    # A room-in-roof window (rooflight) lodges its §11 "Location" cell as
+    # "Roof of Room in Roof", which the layout preprocessor wraps onto two
+    # tokens ("Roof of Room" in the prefix block, "in Roof" in the suffix).
+    # Detected so the window routes to a roof window (worksheet (27a))
+    # and the tokens don't leak into the glazing-type phrase.
+    _ROOF_OF_ROOM_LOCATION_TOKENS = frozenset({"Roof of Room", "in Roof"})
     # The Elmhurst Summary PDF lodges each window's glazing-type as a
     # capitalised phrase like "Double between 2002" / "Double with unknown"
     # / "Single" / "Triple" / "Secondary". The first token of that phrase
@@ -1018,6 +1040,18 @@ class ElmhurstSiteNotesExtractor:
         before = [lines[j].strip() for j in range(before_start, data_idx) if lines[j].strip()]
         after = [lines[j].strip() for j in range(manuf_idx + 4, after_end) if lines[j].strip()]
 
+        # Room-in-roof windows lodge their location as "Roof of Room in
+        # Roof" (wrapped across the prefix/suffix blocks). Detect it, pull
+        # those tokens out so they don't contaminate the glazing-type
+        # phrase, and override the wall-keyed `location` with the roof-of-
+        # room marker the roof-window classifier keys on.
+        if any(
+            t in self._ROOF_OF_ROOM_LOCATION_TOKENS for t in (*before, *after)
+        ):
+            location = "Roof of Room"
+            before = [t for t in before if t not in self._ROOF_OF_ROOM_LOCATION_TOKENS]
+            after = [t for t in after if t not in self._ROOF_OF_ROOM_LOCATION_TOKENS]
+
         glazing_type, building_part, orientation = self._compose_window_descriptors(
             before=before,
             after=after,
@@ -1326,6 +1360,8 @@ class ElmhurstSiteNotesExtractor:
             fan_assisted_flue=self._local_bool(lines, "Fan Assisted Flue"),
             percentage_of_heat=pct,
             main_heating_sap_code=main_heating_sap_code,
+            heat_emitter=self._local_str(lines, "Heat Emitter"),
+            heating_controls_sap=self._local_str(lines, "Main Heating Controls Sap"),
         )
 
     def _extract_community_heating(self) -> Optional[CommunityHeating]:
@@ -1516,6 +1552,7 @@ class ElmhurstSiteNotesExtractor:
             wind_turbines_terrain_type=terrain,
             hydro_electricity_generated_kwh=hydro,
             pv_arrays=self._extract_pv_arrays(),
+            pv_diverter_present=self._bool_val("Diverter present"),
             pv_percent_roof_area=pv_pct if pv_pct > 0 else None,
             solar_hw_collector_orientation=solar_orientation,
             solar_hw_collector_pitch_deg=solar_pitch,

backend/documents_parser/tests/test_summary_pdf_mapper_chain.py

@@ -42,6 +42,7 @@ from datatypes.epc.domain.mapper import (
     EpcPropertyDataMapper,
     UnmappedApiCode,
     UnmappedElmhurstLabel,
+    _elmhurst_glazing_type_code,  # pyright: ignore[reportPrivateUsage]
 )
 from domain.sap10_calculator.calculator import calculate_sap_from_inputs
 from domain.sap10_calculator.rdsap.cert_to_inputs import SAP_10_2_SPEC_PRICES, cert_to_inputs
@@ -1471,6 +1472,68 @@ def test_summary_000474_double_glazed_windows_route_to_code_3() -> None:
         )
 
 
+def test_elmhurst_glazing_label_full_coverage_per_sap10_table_6b() -> None:
+    # Arrange — the double_glazing recommendation fixture (Summary_001431)
+    # exercises every RdSAP-21 §11 glazing-type lodging in one cert. Each
+    # label must resolve to the SAP 10.2 Table 6b cascade code whose
+    # `_G_LIGHT_BY_GLAZING_CODE` daylight factor g_L is correct for the
+    # glazing family: single 0.90, double / secondary 0.80, triple 0.70
+    # (the lodged manufacturer U/g drive §3/§6; the code only sets g_L).
+    expected: dict[str, int] = {
+        "Single glazing": 1,
+        "Single glazing, known data": 15,
+        "Double pre 2002": 2,
+        "Double between 2002 and 2021": 3,
+        "Double with unknown install date": 3,
+        "Double glazing, known data": 3,
+        "Double post or during 2022": 5,
+        "Secondary glazing": 7,
+        "Secondary glazing - Normal emissivity": 11,
+        "Secondary glazing - Low emissivity": 12,
+        "Triple pre 2002": 10,
+        "Triple between 2002 and 2021": 9,
+        "Triple post or during 2022": 6,
+        "Triple with unknown install date": 6,
+    }
+
+    # Act / Assert
+    for label, code in expected.items():
+        assert _elmhurst_glazing_type_code(label) == code, (
+            f"{label!r} should map to SAP 10.2 Table 6b code {code}"
+        )
+
+
+def test_extension_party_wall_type_read_independently_of_as_main_wall() -> None:
+    # Arrange — RdSAP 10 §3.3: "As Main Wall: Yes" inherits only the
+    # external wall CONSTRUCTION; the party wall type is lodged
+    # separately per building part and may differ. The double_glazing
+    # fixture (Summary_001431) lodges Main party "CU Cavity masonry
+    # unfilled" (SAP10 wall_construction 4 → u_party_wall 0.5) but the
+    # 1st Extension party "U Unable to determine" (→ wall_construction 0
+    # → RdSAP default u_party_wall 0.25), even though the extension is
+    # "As Main Wall: Yes". Pre-fix the extension inherited the Main's
+    # party type (both 0.5), inflating worksheet (32) party heat loss.
+    pages = _summary_pdf_to_textract_style_pages(
+        _FIXTURES / "Summary_001431_double_glazing.pdf"
+    )
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+
+    # Act
+    epc = EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)
+
+    # Assert — Main BP keeps cavity-unfilled (4); the extension BP gets
+    # the "Unable to determine" sentinel (0), a distinct party wall U.
+    party_codes = [
+        bp.party_wall_construction for bp in epc.sap_building_parts
+    ]
+    assert party_codes == [4, 0], (
+        f"expected Main=4 (CU, U=0.5) + Ext=0 (Unable, U=0.25), got {party_codes}"
+    )
+    # The two map to different SAP party-wall U-values.
+    assert abs(u_party_wall(4) - 0.5) <= 1e-9
+    assert abs(u_party_wall(0) - 0.25) <= 1e-9
+
+
 def test_summary_mapper_raises_on_unmapped_glazing_type_label() -> None:
     # Arrange — same strict-coverage gate as the cylinder-size helper
     # (Slice S0380.15 + S0380.16): silently routing an unknown glazing
@@ -4330,3 +4393,79 @@ def test_from_elmhurst_site_notes_matches_hand_built_000516() -> None:
         f"hand-built EpcPropertyData for cohort cert 000516:\n  " +
         "\n  ".join(diffs)
     )
+
+
+def test_elmhurst_jacket_cylinder_insulation_maps_to_loose_jacket_code_2() -> None:
+    # Arrange — an Elmhurst §15.1 "Cylinder Insulation Type: Jacket"
+    # lodging is a loose jacket, which SAP 10.2 Table 2 Note 1 gives a
+    # separate (higher) storage-loss factor than factory foam. The SAP10
+    # `cylinder_insulation_type` enum uses 2 for loose jacket (1 = factory
+    # foam), matching the GOV.UK API path — so the Summary "Jacket" label
+    # must resolve to 2 for cross-mapper parity, and so the
+    # loose-jacket storage-loss branch (S0380.224) fires. Observed on the
+    # simulated-case-19 worksheet (210 L jacket cylinder + storage heaters).
+    from datatypes.epc.domain.mapper import _elmhurst_cylinder_insulation_code  # pyright: ignore[reportPrivateUsage]
+
+    # Act
+    code = _elmhurst_cylinder_insulation_code("Jacket", cylinder_present=True)
+
+    # Assert
+    assert code == 2
+
+
+def test_elmhurst_foam_cylinder_insulation_still_maps_to_factory_code_1() -> None:
+    # Arrange — regression guard: the factory-foam label is unchanged.
+    from datatypes.epc.domain.mapper import _elmhurst_cylinder_insulation_code  # pyright: ignore[reportPrivateUsage]
+
+    # Act
+    code = _elmhurst_cylinder_insulation_code("Foam", cylinder_present=True)
+
+    # Assert
+    assert code == 1
+
+
+def test_elmhurst_roof_construction_int_matches_api_codes() -> None:
+    # Arrange — cross-mapper structural parity: the gov-EPC API mapper
+    # populates BOTH roof_construction (int) and roof_construction_type
+    # (str derived via `_API_ROOF_CONSTRUCTION_TO_STR`), but the Elmhurst
+    # mapper set only the string, leaving the int None. The SAP cascade
+    # reads the string (so SAP parity held), but consumers of the int
+    # (e.g. domain/sap10_ml ML aggregates) saw None on every site-notes
+    # cert. `_elmhurst_roof_construction_int` closes the gap, mapping the
+    # Elmhurst roof code to the same SAP10 int the API lodges. Unmapped
+    # codes return None (not a raise) — the int is not cascade-load-
+    # bearing, so an unknown roof must not block the cert.
+    from datatypes.epc.domain.mapper import _elmhurst_roof_construction_int  # pyright: ignore[reportPrivateUsage]
+
+    # Act / Assert — each Elmhurst roof code → the gov-EPC API int.
+    assert _elmhurst_roof_construction_int("F Flat") == 1
+    assert _elmhurst_roof_construction_int("PN Pitched (slates/tiles), no access") == 3
+    assert _elmhurst_roof_construction_int("PA Pitched (slates/tiles), access to loft") == 4
+    assert _elmhurst_roof_construction_int("PS Pitched, sloping ceiling") == 8
+    assert _elmhurst_roof_construction_int("S Same dwelling above") == 7
+    assert _elmhurst_roof_construction_int("A Another dwelling above") == 7
+    # Absent / unmapped → None (no raise; not cascade-load-bearing).
+    assert _elmhurst_roof_construction_int(None) is None
+    assert _elmhurst_roof_construction_int("") is None
+    assert _elmhurst_roof_construction_int("NR Non-residential space above") is None
+
+
+def test_elmhurst_wall_is_basement_disambiguates_system_built_from_basement() -> None:
+    # Arrange — "SY System build" and "B Basement wall" both map to SAP10
+    # wall_construction=6 (canonical WALL_SYSTEM_BUILT). The explicit
+    # basement flag separates them: only "B" is a basement wall (drives
+    # RdSAP §5.17 u_basement_wall); "SY" is False so it routes through the
+    # normal system-built U-value table; any other code → None (the
+    # gov-EPC API code-6 heuristic still applies).
+    from datatypes.epc.domain.mapper import _elmhurst_wall_construction_int  # pyright: ignore[reportPrivateUsage]
+    from datatypes.epc.domain.mapper import _elmhurst_wall_is_basement  # pyright: ignore[reportPrivateUsage]
+
+    # Act / Assert — system-built keeps code 6 but is NOT basement.
+    assert _elmhurst_wall_construction_int("SY System build") == 6
+    assert _elmhurst_wall_is_basement("SY System build") is False
+    # Genuine basement: code 6 AND flagged basement.
+    assert _elmhurst_wall_construction_int("B Basement wall") == 6
+    assert _elmhurst_wall_is_basement("B Basement wall") is True
+    # Other constructions defer to the API code-6 heuristic.
+    assert _elmhurst_wall_is_basement("CA Cavity") is None
+    assert _elmhurst_wall_is_basement("") is None

datatypes/epc/domain/epc_property_data.py

@@ -324,6 +324,11 @@ class SapEnergySource:
     photovoltaic_arrays: Optional[List[PhotovoltaicArray]] = None
     wind_turbine_details: Optional[WindTurbineDetails] = None
     pv_batteries: Optional[PvBatteries] = None
+    # SAP 10.2 Appendix G4 — a PV diverter present on the dwelling routes
+    # surplus PV to a hot-water cylinder immersion. Drives worksheet
+    # (63b)m. Set from the API `sap_energy_source.pv_diverter` flag or the
+    # Elmhurst Summary §19 "Diverter present" row.
+    pv_diverter_present: bool = False
 
 
 @dataclass
@@ -435,13 +440,24 @@ class SapAlternativeWall:
     # Mirrors `SapBuildingPart.wall_thickness_mm` per the
     # [[feedback-no-misleading-insulation-type]] convention.
     wall_thickness_mm: Optional[int] = None
+    # Explicit basement determination. RdSAP10 `wall_construction == 6` is
+    # canonically SYSTEM-BUILT (`WALL_SYSTEM_BUILT`) — the basement
+    # heuristic hijacked it because Elmhurst lodges both "SY System build"
+    # and "B Basement wall" as code 6. When the source can tell them apart
+    # (the Elmhurst mapper, from the distinct "SY"/"B" codes) it sets this
+    # flag; None falls back to the gov-EPC API code-6 heuristic so the API
+    # path (basement lodged as integer 6, no flag) is unchanged.
+    is_basement: Optional[bool] = None
 
     @property
     def is_basement_wall(self) -> bool:
-        """True iff this alt sub-area is the dwelling's basement wall —
-        identified by RdSAP10 wall_construction code = 6 (see module
-        constant `BASEMENT_WALL_CONSTRUCTION_CODE`). RdSAP §5.17 / Table 23
-        applies a special U-value lookup to basement walls."""
+        """True iff this alt sub-area is the dwelling's basement wall.
+        Honours the explicit `is_basement` flag when set; otherwise falls
+        back to the gov-EPC API basement sentinel `wall_construction == 6`
+        (`BASEMENT_WALL_CONSTRUCTION_CODE`). RdSAP §5.17 / Table 23 applies
+        a special U-value lookup to basement walls."""
+        if self.is_basement is not None:
+            return self.is_basement
         return self.wall_construction == BASEMENT_WALL_CONSTRUCTION_CODE
 
 
@@ -472,7 +488,15 @@ class SapBuildingPart:
     )
     wall_dry_lined: Optional[bool] = None  # Don't think we have this in site notes
     wall_thickness_mm: Optional[int] = None
-    wall_insulation_thickness: Optional[str] = None
+    # Union[str, int]: a numeric mm value when the API lodges
+    # `wall_insulation_thickness == "measured"` (resolved from the
+    # separate measured field), else the lodged string ("NI", a numeric
+    # string, etc.). Mirrors `roof_insulation_thickness`.
+    wall_insulation_thickness: Optional[Union[str, int]] = None
+    # RdSAP 10 §5.8 thermal-conductivity code for measured wall insulation
+    # (λ = 0.04 / 0.03 / 0.025 W/m·K). Used by the documentary-evidence
+    # R-value path when a measured wall thickness is lodged alongside it.
+    wall_insulation_thermal_conductivity: Optional[Union[str, int]] = None
     sap_alternative_wall_1: Optional[SapAlternativeWall] = None
     sap_alternative_wall_2: Optional[SapAlternativeWall] = None
 
@@ -506,12 +530,23 @@ class SapBuildingPart:
     # The dwelling-wide `construction_age_band` does NOT govern curtain
     # walls; this field decouples them per spec.
     curtain_wall_age: Optional[str] = None
+    # Explicit basement determination for the primary wall. See
+    # `SapAlternativeWall.is_basement` — RdSAP10 code 6 is canonically
+    # SYSTEM-BUILT, so the Elmhurst mapper sets this flag from the distinct
+    # "SY"/"B" codes (False for system-built, True for basement); None
+    # preserves the gov-EPC API code-6 heuristic.
+    wall_is_basement: Optional[bool] = None
 
     @property
     def main_wall_is_basement(self) -> bool:
         """True iff this part's primary wall (not an alt sub-area) is the
         basement wall — happens when the whole part sits below grade.
-        Empirically 54 of 67k parts in the 2026 sweep; rare but real."""
+        Empirically 54 of 67k parts in the 2026 sweep; rare but real.
+        Honours the explicit `wall_is_basement` flag when set (so a
+        SYSTEM-BUILT wall, which shares code 6, is not mis-flagged);
+        otherwise falls back to the gov-EPC API code-6 heuristic."""
+        if self.wall_is_basement is not None:
+            return self.wall_is_basement
         return self.wall_construction == BASEMENT_WALL_CONSTRUCTION_CODE
 
     @property
@@ -714,3 +749,25 @@ class EpcPropertyData:
     solar_hw_collector_orientation: Optional[str] = None
     solar_hw_collector_pitch_deg: Optional[int] = None
     solar_hw_overshading: Optional[str] = None
+
+    @property
+    def system_build(self) -> Optional[bool]:
+        """Whether the dwelling's MAIN wall is system-built.
+
+        System-built is a WALL TYPE: RdSAP10 `WALL_SYSTEM_BUILT == 6` on
+        the main wall (the U-value cascade table is keyed on that code).
+        It happens to share the integer with basement walls — so a code-6
+        main wall is system-built only when it is NOT flagged as a
+        basement (`main_wall_is_basement`, the dedicated basement signal
+        the mapper sets from the distinct "SY"/"B" labels or the cert
+        addendum). Reading the wall type keeps the two concerns separate:
+        `wall_construction` carries the construction, the basement flag
+        carries the below-grade attribute. Returns None when there is no
+        MAIN building part (unknown)."""
+        for part in self.sap_building_parts:
+            if part.identifier is BuildingPartIdentifier.MAIN:
+                return (
+                    part.wall_construction == BASEMENT_WALL_CONSTRUCTION_CODE
+                    and not part.main_wall_is_basement
+                )
+        return None

datatypes/epc/domain/mapper.py

@@ -1,10 +1,12 @@
 import re
+from dataclasses import replace
 from datetime import date
 from decimal import ROUND_HALF_UP, Decimal
 from typing import Any, Dict, Final, List, Optional, Sequence, Union, cast
 from datatypes.epc.schema.helpers import from_dict
 
 from datatypes.epc.domain.epc_property_data import (
+    BASEMENT_WALL_CONSTRUCTION_CODE,
     Addendum,
     BuildingPartIdentifier,
     EnergyElement,
@@ -341,6 +343,7 @@ class EpcPropertyDataMapper:
                 wind_turbines_terrain_type=survey.renewables.wind_turbines_terrain_type,
                 electricity_smart_meter_present=survey.meters.electricity_smart_meter,
                 photovoltaic_arrays=_elmhurst_pv_arrays(survey.renewables),
+                pv_diverter_present=survey.renewables.pv_diverter_present,
                 # RdSAP 10 §11.1 b): when the cert lodges only a "% of
                 # roof area" PV figure (no detailed kWp / orientation),
                 # surface it through `photovoltaic_supply` so the
@@ -560,7 +563,13 @@ class EpcPropertyDataMapper:
                     building_part_number=bp.building_part_number,
                     wall_dry_lined=bp.wall_dry_lined == "Y",
                     wall_thickness_mm=bp.wall_thickness,
-                    wall_insulation_thickness=bp.wall_insulation_thickness,
+                    wall_insulation_thickness=_api_resolve_wall_insulation_thickness(
+                        bp.wall_insulation_thickness,
+                        getattr(bp, "wall_insulation_thickness_measured", None),
+                    ),
+                    wall_insulation_thermal_conductivity=getattr(
+                        bp, "wall_insulation_thermal_conductivity", None
+                    ),
                     floor_heat_loss=bp.floor_heat_loss,
                     floor_insulation_thickness=None,
                     roof_construction=bp.roof_construction,
@@ -693,7 +702,13 @@ class EpcPropertyDataMapper:
                     building_part_number=bp.building_part_number,
                     wall_dry_lined=bp.wall_dry_lined == "Y",
                     wall_thickness_mm=bp.wall_thickness,
-                    wall_insulation_thickness=bp.wall_insulation_thickness,
+                    wall_insulation_thickness=_api_resolve_wall_insulation_thickness(
+                        bp.wall_insulation_thickness,
+                        getattr(bp, "wall_insulation_thickness_measured", None),
+                    ),
+                    wall_insulation_thermal_conductivity=getattr(
+                        bp, "wall_insulation_thermal_conductivity", None
+                    ),
                     floor_heat_loss=bp.floor_heat_loss,
                     floor_insulation_thickness=None,
                     roof_construction=bp.roof_construction,
@@ -826,7 +841,13 @@ class EpcPropertyDataMapper:
                     building_part_number=bp.building_part_number,
                     wall_dry_lined=bp.wall_dry_lined == "Y",
                     wall_thickness_mm=bp.wall_thickness,
-                    wall_insulation_thickness=bp.wall_insulation_thickness,
+                    wall_insulation_thickness=_api_resolve_wall_insulation_thickness(
+                        bp.wall_insulation_thickness,
+                        getattr(bp, "wall_insulation_thickness_measured", None),
+                    ),
+                    wall_insulation_thermal_conductivity=getattr(
+                        bp, "wall_insulation_thermal_conductivity", None
+                    ),
                     floor_heat_loss=bp.floor_heat_loss,
                     # API certs commonly lodge "NI" (no measured
                     # thickness) on floors that aren't actually
@@ -985,7 +1006,13 @@ class EpcPropertyDataMapper:
                     building_part_number=bp.building_part_number,
                     wall_dry_lined=bp.wall_dry_lined == "Y",
                     wall_thickness_mm=bp.wall_thickness,
-                    wall_insulation_thickness=bp.wall_insulation_thickness,
+                    wall_insulation_thickness=_api_resolve_wall_insulation_thickness(
+                        bp.wall_insulation_thickness,
+                        getattr(bp, "wall_insulation_thickness_measured", None),
+                    ),
+                    wall_insulation_thermal_conductivity=getattr(
+                        bp, "wall_insulation_thermal_conductivity", None
+                    ),
                     floor_heat_loss=bp.floor_heat_loss,
                     # API certs commonly lodge "NI" (no measured
                     # thickness) on floors that aren't actually
@@ -1161,7 +1188,13 @@ class EpcPropertyDataMapper:
                     building_part_number=bp.building_part_number,
                     wall_dry_lined=bp.wall_dry_lined == "Y",
                     wall_thickness_mm=bp.wall_thickness,
-                    wall_insulation_thickness=bp.wall_insulation_thickness,
+                    wall_insulation_thickness=_api_resolve_wall_insulation_thickness(
+                        bp.wall_insulation_thickness,
+                        getattr(bp, "wall_insulation_thickness_measured", None),
+                    ),
+                    wall_insulation_thermal_conductivity=getattr(
+                        bp, "wall_insulation_thermal_conductivity", None
+                    ),
                     floor_heat_loss=bp.floor_heat_loss,
                     # API certs commonly lodge "NI" (no measured
                     # thickness) on floors that aren't actually
@@ -1361,6 +1394,7 @@ class EpcPropertyDataMapper:
                     else None
                 ),
                 pv_batteries=_first_pv_battery(es.pv_batteries),
+                pv_diverter_present=es.pv_diverter == "true",
             ),
             sap_building_parts=[
                 SapBuildingPart(
@@ -1378,7 +1412,13 @@ class EpcPropertyDataMapper:
                     building_part_number=bp.building_part_number,
                     wall_dry_lined=bp.wall_dry_lined == "Y",
                     wall_thickness_mm=bp.wall_thickness,
-                    wall_insulation_thickness=bp.wall_insulation_thickness,
+                    wall_insulation_thickness=_api_resolve_wall_insulation_thickness(
+                        bp.wall_insulation_thickness,
+                        getattr(bp, "wall_insulation_thickness_measured", None),
+                    ),
+                    wall_insulation_thermal_conductivity=getattr(
+                        bp, "wall_insulation_thermal_conductivity", None
+                    ),
                     floor_heat_loss=bp.floor_heat_loss,
                     # API certs commonly lodge "NI" (no measured
                     # thickness) on floors that aren't actually
@@ -1587,10 +1627,24 @@ class EpcPropertyDataMapper:
                     schema.sap_heating.shower_outlets, _API_SHOWER_OUTLET_CODE_MIXER,
                 ),
             ),
-            # SAP windows
+            # SAP windows — split vertical wall windows (27) from roof
+            # windows (27a) on the RdSAP `window_wall_type=4` signal.
             sap_windows=[
-                _api_sap_window(w) for w in schema.sap_windows
+                _api_sap_window(w)
+                for w in schema.sap_windows
+                if not _api_is_roof_window(w)
             ],
+            # Empty → None (not []) so "no roof windows" has the single
+            # canonical representation the domain field defaults to
+            # (`Optional[List] = None`), matching the 21.0.0 path and the
+            # persistence round-trip (roof windows aren't yet stored — doc
+            # §2.4 — so a reloaded cert always reads None here).
+            sap_roof_windows=[
+                _api_sap_roof_window(w)
+                for w in schema.sap_windows
+                if _api_is_roof_window(w)
+            ]
+            or None,
             # SAP energy source
             sap_energy_source=SapEnergySource(
                 mains_gas=es.mains_gas == "Y",
@@ -1614,6 +1668,7 @@ class EpcPropertyDataMapper:
                     else None
                 ),
                 pv_batteries=_first_pv_battery(es.pv_batteries),
+                pv_diverter_present=es.pv_diverter == "true",
             ),
             # SAP building parts
             sap_building_parts=[
@@ -1632,7 +1687,13 @@ class EpcPropertyDataMapper:
                     building_part_number=bp.building_part_number,
                     wall_dry_lined=bp.wall_dry_lined == "Y",
                     wall_thickness_mm=bp.wall_thickness,
-                    wall_insulation_thickness=bp.wall_insulation_thickness,
+                    wall_insulation_thickness=_api_resolve_wall_insulation_thickness(
+                        bp.wall_insulation_thickness,
+                        getattr(bp, "wall_insulation_thickness_measured", None),
+                    ),
+                    wall_insulation_thermal_conductivity=getattr(
+                        bp, "wall_insulation_thermal_conductivity", None
+                    ),
                     floor_heat_loss=bp.floor_heat_loss,
                     # API certs commonly lodge "NI" (no measured
                     # thickness) on floors that aren't actually
@@ -1861,18 +1922,23 @@ class EpcPropertyDataMapper:
         """
 
         data = _normalize_shower_outlets(data)
+        data = _default_missing_post_town(data)
         schema = data.get("schema_type", "")
         if schema == "RdSAP-Schema-21.0.1":
             from datatypes.epc.schema.rdsap_schema_21_0_1 import RdSapSchema21_0_1
 
-            return EpcPropertyDataMapper.from_rdsap_schema_21_0_1(
-                from_dict(RdSapSchema21_0_1, data)
+            return _clear_basement_flag_when_system_built(
+                EpcPropertyDataMapper.from_rdsap_schema_21_0_1(
+                    from_dict(RdSapSchema21_0_1, data)
+                )
             )
         if schema == "RdSAP-Schema-21.0.0":
             from datatypes.epc.schema.rdsap_schema_21_0_0 import RdSapSchema21_0_0
 
-            return EpcPropertyDataMapper.from_rdsap_schema_21_0_0(
-                from_dict(RdSapSchema21_0_0, data)
+            return _clear_basement_flag_when_system_built(
+                EpcPropertyDataMapper.from_rdsap_schema_21_0_0(
+                    from_dict(RdSapSchema21_0_0, data)
+                )
             )
         raise ValueError(f"Unsupported EPC schema: {schema!r}")
 
@@ -1882,6 +1948,68 @@ class EpcPropertyDataMapper:
 # ---------------------------------------------------------------------------
 
 
+def _clear_basement_flag_when_system_built(
+    epc: EpcPropertyData,
+) -> EpcPropertyData:
+    """When the dwelling is system-built, a `wall_construction == 6` wall
+    is WALL_SYSTEM_BUILT, not a basement — so the gov-EPC API code-6
+    basement heuristic must not fire for it. The API path can't tell the
+    two apart at the per-wall level (both lodge code 6), so once the
+    cert-level `system_build` flag is known we clear the basement signal
+    on every code-6 wall that hasn't been explicitly determined
+    (`wall_is_basement` / `is_basement` still None). No-op unless the
+    dwelling is system-built, so genuine basements (system_build absent /
+    False) keep the code-6 heuristic. Returns the same object when
+    nothing changes.
+
+    The Elmhurst path sets the per-wall flag directly from the distinct
+    "SY"/"B" labels, so it never reaches here (it routes through
+    `from_elmhurst_site_notes`, not `from_api_response`).
+
+    Keyed on the RAW cert `addendum.system_build` signal rather than the
+    derived `epc.system_build` property — the property reads the wall
+    type AFTER this clears the basement flag, so using it here would be
+    circular."""
+    if epc.addendum is None or epc.addendum.system_build is not True:
+        return epc
+
+    def _clear_alt(alt: Optional[SapAlternativeWall]) -> Optional[SapAlternativeWall]:
+        if (
+            alt is not None
+            and alt.is_basement is None
+            and alt.wall_construction == BASEMENT_WALL_CONSTRUCTION_CODE
+        ):
+            return replace(alt, is_basement=False)
+        return alt
+
+    new_parts: List[SapBuildingPart] = []
+    changed = False
+    for part in epc.sap_building_parts:
+        new_alt_1 = _clear_alt(part.sap_alternative_wall_1)
+        new_alt_2 = _clear_alt(part.sap_alternative_wall_2)
+        clear_main = (
+            part.wall_is_basement is None
+            and part.wall_construction == BASEMENT_WALL_CONSTRUCTION_CODE
+        )
+        if clear_main or new_alt_1 is not part.sap_alternative_wall_1 or (
+            new_alt_2 is not part.sap_alternative_wall_2
+        ):
+            changed = True
+            new_parts.append(
+                replace(
+                    part,
+                    wall_is_basement=False if clear_main else part.wall_is_basement,
+                    sap_alternative_wall_1=new_alt_1,
+                    sap_alternative_wall_2=new_alt_2,
+                )
+            )
+        else:
+            new_parts.append(part)
+    if not changed:
+        return epc
+    return replace(epc, sap_building_parts=new_parts)
+
+
 def _measurement_value(field: Any) -> float:
     """SAP measurements arrive as a `Measurement` (with `.value`), a raw dict
     {'value': N, 'quantity': '...'} when `from_dict` didn't coerce, or a plain
@@ -2031,6 +2159,26 @@ def _normalize_shower_outlets(data: Dict[str, Any]) -> Dict[str, Any]:
     return {**data, "sap_heating": new_sap_heating}
 
 
+def _default_missing_post_town(data: Dict[str, Any]) -> Dict[str, Any]:
+    """Default an absent top-level `post_town` to "" before `from_dict`.
+
+    `RdSapSchema21_0_x.post_town` is a required (no-default) field, so a
+    real-API cert that omits it (observed on a 2026-register cert whose
+    town sits only in `address_line_3`) makes `from_dict` raise
+    "missing required field 'post_town'", blocking the whole cert.
+    `post_town` is address metadata that the SAP cascade never reads, so
+    defaulting it to "" is inert for the calculation while keeping the
+    cert mappable. The schema dataclass can't simply give the field a
+    default — it is a plain (non-kw_only) dataclass with 57 required
+    fields after `post_town`, so a mid-list default would break field
+    ordering; pre-processing here mirrors `_normalize_shower_outlets`.
+
+    Mutates a shallow copy so the caller's dict is untouched."""
+    if "post_town" in data:
+        return data
+    return {**data, "post_town": ""}
+
+
 def _count_shower_outlets_by_type(
     schema_shower_outlets: Any, target_type: int,
 ) -> Optional[int]:
@@ -2090,6 +2238,10 @@ _ELMHURST_WALL_CODE_TO_SAP10: Dict[str, int] = {
     "SG": 1,   # Stone: granite or whinstone (cert 000565 Ext1) — the
                # granite-specific Elmhurst variant of "ST"; same SAP10
                # WALL_STONE_GRANITE=1 cascade entry.
+    "SS": 2,   # Stone: sandstone or limestone (simulated case 5 / cert
+               # 0240 archetype) — SAP10 WALL_STONE_SANDSTONE=2. The
+               # sandstone-specific Elmhurst variant; the API path lodges
+               # the same wall as integer wall_construction=2.
     "SB": 3,   # Solid brick (cohort cert lodgement)
     "SO": 3,   # Solid brick (newer Elmhurst PDF variant — same SAP10
                # mapping; cert 9501 lodges "SO Solid Brick" where the
@@ -2097,16 +2249,16 @@ _ELMHURST_WALL_CODE_TO_SAP10: Dict[str, int] = {
     "CA": 4,   # Cavity
     "TF": 5,   # Timber frame
     "TI": 5,   # Timber frame (Elmhurst's alt-wall code; same SAP10 mapping)
-    "SY": 6,   # System build
-    "B":  6,   # Basement wall (cert 000565 Ext3+Ext4) — routes to the
-               # `BASEMENT_WALL_CONSTRUCTION_CODE=6` canonical signal so
-               # the cascade's `part.main_wall_is_basement` triggers the
-               # RdSAP 10 §5.17 / Table 23 `u_basement_wall` override
-               # (heat_transmission.py:640). Collides numerically with
-               # "SY" System build — the cascade's basement check
-               # precedes `u_wall(construction=6)` so SY would be
-               # silently mis-routed to u_basement_wall today; no cohort
-               # fixture exercises SY yet so the conflict is dormant.
+    "SY": 6,   # System build — canonical RdSAP10 WALL_SYSTEM_BUILT=6.
+    "B":  6,   # Basement wall (cert 000565 Ext3+Ext4). Numerically
+               # collides with "SY" System build on code 6, so the
+               # basement vs system-built distinction is carried by the
+               # explicit `is_basement` / `wall_is_basement` flag (set
+               # via `_elmhurst_wall_is_basement`) rather than the code:
+               # only "B" triggers the cascade's `main_wall_is_basement`
+               # → RdSAP 10 §5.17 / Table 23 `u_basement_wall` override.
+               # "SY" sets the flag False so it routes through the normal
+               # `u_wall(construction=6)` system-built table instead.
     "CO": 7,   # Cob
     "PH": 8,   # Park home
     "CW": 9,   # Curtain wall
@@ -2171,6 +2323,40 @@ def _elmhurst_dwelling_type(
     return f"{position} flat"
 
 
+# Elmhurst roof-type codes → SAP10 roof_construction integer, matching the
+# gov-EPC API codes in `_API_ROOF_CONSTRUCTION_TO_STR` so the two
+# front-ends populate the same field. Harvested from the committed
+# Elmhurst Summary fixtures (corpus + cohort): F/PN/PA/PS/S/A. Vaulted (5)
+# and thatched (6) are omitted until a fixture surfaces their Elmhurst
+# codes. NR ("Non-residential space above") is intentionally left
+# unmapped — the gov enum's code 7 is specifically "dwelling above".
+_ELMHURST_ROOF_CODE_TO_SAP10: Dict[str, int] = {
+    "F": 1,    # Flat
+    "PN": 3,   # Pitched (slates/tiles), no access (to loft)
+    "PA": 4,   # Pitched (slates/tiles), access to loft
+    "PS": 8,   # Pitched, sloping ceiling
+    "S": 7,    # Same dwelling above
+    "A": 7,    # Another dwelling above
+}
+
+
+def _elmhurst_roof_construction_int(coded: Optional[str]) -> Optional[int]:
+    """Map an Elmhurst roof_type string ('PA Pitched (slates/tiles),
+    access to loft') to the SAP10 `roof_construction` integer the gov-EPC
+    API lodges (4), so the site-notes and API front-ends populate the
+    same field (cross-mapper structural parity).
+
+    Returns None for an absent or unmapped code — and, unlike
+    `_elmhurst_wall_construction_int`, does NOT raise. `roof_construction`
+    (int) is not read by the SAP cascade (which reads the string
+    `roof_construction_type`, populated on both paths), so an unmapped
+    roof code stays None — the pre-existing Elmhurst behaviour — rather
+    than blocking the cert."""
+    if not coded:
+        return None
+    return _ELMHURST_ROOF_CODE_TO_SAP10.get(_leading_code(coded))
+
+
 def _elmhurst_wall_construction_int(coded: str) -> Optional[int]:
     """Map an Elmhurst wall_type string ('CA Cavity') to the SAP10
     integer code (4). Returns None when the lodging is absent (empty
@@ -2188,6 +2374,32 @@ def _elmhurst_wall_construction_int(coded: str) -> Optional[int]:
     return _ELMHURST_WALL_CODE_TO_SAP10[code]
 
 
+# Elmhurst wall codes that both resolve to SAP10 wall_construction=6 but
+# carry opposite basement meaning: "B" Basement wall vs "SY" System build
+# (see `_ELMHURST_WALL_CODE_TO_SAP10`). RdSAP10 code 6 is canonically
+# WALL_SYSTEM_BUILT; the explicit basement flag lets the cascade route a
+# genuine basement to RdSAP §5.17 `u_basement_wall` without mis-flagging
+# a system-built wall.
+_ELMHURST_BASEMENT_WALL_CODE: Final[str] = "B"
+_ELMHURST_SYSTEM_BUILT_WALL_CODE: Final[str] = "SY"
+
+
+def _elmhurst_wall_is_basement(coded: str) -> Optional[bool]:
+    """Disambiguate the SAP10 code-6 collision from the Elmhurst wall_type
+    string. Returns True for "B Basement wall", False for "SY System
+    build", and None for every other code (so the SapBuildingPart /
+    SapAlternativeWall properties fall back to the gov-EPC API code-6
+    heuristic — unchanged for the API path). Empty lodging → None."""
+    code = _leading_code(coded)
+    if not code:
+        return None
+    if code == _ELMHURST_BASEMENT_WALL_CODE:
+        return True
+    if code == _ELMHURST_SYSTEM_BUILT_WALL_CODE:
+        return False
+    return None
+
+
 # Elmhurst Party Wall Type codes — distinct category-set from the Wall
 # Type field; the codes describe construction class for `u_party_wall`
 # (Table 4 / RdSAP §S.3.2) rather than a specific SAP10 wall-type. Maps
@@ -2319,9 +2531,33 @@ def _api_party_wall_construction_int(value: Union[int, str, None]) -> Optional[i
 # distinguishes "Suspended" vs everything-else (the solid-branch is
 # the default fall-through), so the additional code maps to the same
 # "Solid" string as code 1.
-_API_FLOOR_CONSTRUCTION_TO_STR: Dict[int, str] = {
+# Code 3 = "suspended, not timber" (e.g. beam-and-block / suspended
+# concrete). RdSAP 10 field 3-1 "Floor construction" enumerates the
+# lowest-floor construction as solid / suspended timber / suspended,
+# not timber. The timber/not-timber split is load-bearing: the spec's
+# "Suspended not timber (structural infiltration 0)" means only
+# "Suspended timber" triggers the §5 (12) 0.1/0.2 floor-infiltration
+# adjustment (see `_has_suspended_timber_floor_per_spec`), while a
+# not-timber suspended floor is infiltration 0. Mapping to the canonical
+# "Suspended, not timber" string (also used by the site-notes mapper)
+# takes the suspended U-value branch via the "Suspended" prefix yet
+# correctly fails the exact-match timber gate. Observed on 53/1000 of a
+# random 2026 API sample (was raising UnmappedApiCode, blocking the cert).
+#
+# Code 0 = "not recorded / not applicable" → None. It pairs
+# overwhelmingly with floor_heat_loss=6 ("another dwelling below" — an
+# upper-floor flat with no ground floor to describe) but also appears
+# with mixed Solid / unheated-space descriptions, so there is no single
+# construction to assert. None defers to RdSAP 10 Table 19 ("where floor
+# construction is unknown" → age-band default), exactly as an unlodged
+# floor_construction does. Empirically inert: floor W/K is identical to
+# any explicit construction across all 37 code-0 certs in the 2026
+# sample (the heat loss is governed by floor_heat_loss, not this field).
+_API_FLOOR_CONSTRUCTION_TO_STR: Dict[int, Optional[str]] = {
+    0: None,
     1: "Solid",
     2: "Suspended timber",
+    3: "Suspended, not timber",
     4: "Solid",
 }
 
@@ -2334,11 +2570,28 @@ _API_FLOOR_CONSTRUCTION_TO_STR: Dict[int, str] = {
 # are observed on cert 001479; the wider RdSAP10 roof-construction
 # enum (1=Flat, 3=Pitched no-access, 5=Vaulted, etc.) is mapped as
 # best-effort against SAP10 nomenclature.
-_API_ROOF_CONSTRUCTION_TO_STR: Dict[int, str] = {
+#
+# Codes 6 and 7 → None. This field is read ONLY for the sloping-ceiling
+# inclined factor; the base roof U-value comes from the global
+# roofs[].description, so a non-sloping code carries no information the
+# cascade consumes here, and None correctly avoids the cos(30°) false-
+# trigger:
+#   6 = "Thatched, with additional insulation" — its U is set by the
+#       global description; not a sloping ceiling.
+#   7 = "(same dwelling above)" / "(another dwelling above)" — an
+#       internal ceiling with no roof heat loss (the roof-side analogue
+#       of floor_construction code 0). Heat loss is governed by the
+#       roof_heat_loss / description path, not this field.
+# Empirically inert: roof W/K is identical whether 6/7 map to None or to
+# an explicit pitched string across all code-6/7 certs in the 2026
+# sample (were raising UnmappedApiCode, blocking the cert).
+_API_ROOF_CONSTRUCTION_TO_STR: Dict[int, Optional[str]] = {
     1: "Flat",
     3: "Pitched (slates/tiles), no access to loft",
     4: "Pitched (slates/tiles), access to loft",
     5: "Pitched (vaulted ceiling)",
+    6: None,
+    7: None,
     8: "Pitched, sloping ceiling",
 }
 
@@ -2627,6 +2880,50 @@ def _api_secondary_fuel_type(
     return lodged_fuel_type
 
 
+# RdSAP API `window_wall_type` code 4 = roof window ("Roof of Room"
+# rooflight / inclined glazing). Codes 1=main wall, 2=alt wall 1, 3=alt
+# wall 2 (see `_window_on_alt_wall`). A roof window is billed on worksheet
+# (27a) at the Table 6e Note 2 inclination-adjusted U and draws 45°-
+# inclined solar gains, NOT on (27) as vertical glazing. Cert 0240's 6
+# "Roof of Room" windows lodge this code; the simulated-case-6 worksheet
+# confirms the (27a) treatment at U_eff 2.1062.
+_API_WINDOW_WALL_TYPE_ROOF: Final[int] = 4
+
+
+def _api_is_roof_window(w: Any) -> bool:
+    """True when an API sap_windows entry is a roof window (rooflight),
+    keyed on `window_wall_type == 4`. `window_type` is NOT the signal —
+    certs 0390 / 7536 lodge `window_type=2` on ordinary main-wall
+    (wall_type=1) windows."""
+    return w.window_wall_type == _API_WINDOW_WALL_TYPE_ROOF
+
+
+def _api_sap_roof_window(w: Any) -> SapRoofWindow:
+    """Build a `SapRoofWindow` from one API roof-window entry
+    (`window_wall_type=4`). The lodged glazing type gives the vertical
+    U / g / frame-factor via the same SAP 10.2 Table 24 lookup the
+    vertical-window path uses; the U is then raised by the SAP 10.2
+    Table 6e Note 2 inclination adjustment (+0.30 W/m²K at 45° pitch) to
+    the inclined-position value the worksheet bills on (27a). Mirror of
+    the site-notes `_map_elmhurst_roof_window`."""
+    transmission = _api_glazing_transmission(w.glazing_type, w.glazing_gap)
+    vertical_u = transmission[0] if transmission is not None else 2.0
+    g_perp = transmission[1] if transmission is not None else 0.76
+    frame_factor = w.frame_factor
+    if frame_factor is None:
+        frame_factor = transmission[2] if transmission is not None else 0.70
+    return SapRoofWindow(
+        area_m2=_measurement_value(w.window_width) * _measurement_value(w.window_height),
+        u_value_raw=vertical_u + _ELMHURST_ROOF_WINDOW_INCLINATION_ADJUSTMENT_W_PER_M2K,
+        orientation=w.orientation,
+        pitch_deg=45.0,
+        g_perpendicular=g_perp,
+        frame_factor=frame_factor,
+        glazing_type=_api_cascade_glazing_type(w.glazing_type),
+        window_location=w.window_location,
+    )
+
+
 def _api_sap_window(w: Any) -> SapWindow:
     """Build a `SapWindow` from one API schema sap_windows entry,
     routing the glazing-type + glazing-gap pair through the spec
@@ -2710,20 +3007,84 @@ def _api_build_sap_floor_dimensions(
     return out
 
 
+# RdSAP 10 §3.9.1 (PDF p.21): a Simplified Type 1 RR gable has no measured
+# height — the worksheet applies the default RR storey height of 2.45 m, so
+# the gable area is L × 2.45 (cert 6035 Summary lodges H=2.45 explicitly,
+# matching this default; gable area 4.65 × 2.45 = 11.39 m²).
+_RIR_TYPE_1_GABLE_HEIGHT_M: Final[float] = 2.45
+
+# GOV.UK API `room_in_roof_type_1.gable_wall_type_*` integer → the
+# `SapRoomInRoofSurface.kind` the cascade's Detailed-RR branch routes by
+# U-value. Established from cert 6035's Summary (gable_wall_type_1=1 ↔
+# "Exposed" U=0.29; gable_wall_type_2=0 ↔ "Party" U=0.25):
+#   0 = Party    → `gable_wall`          (Table 4 p.22 row 2, U=0.25)
+#   1 = Exposed  → `gable_wall_external` (Table 4 p.22 row 1, "as common wall")
+_API_TYPE_1_GABLE_TYPE_TO_KIND: Dict[int, str] = {
+    0: "gable_wall",
+    1: "gable_wall_external",
+}
+
+
+def _api_type_1_gable_kind(gable_type: Optional[int]) -> str:
+    """Map a `gable_wall_type_*` code to the cascade's RR surface kind.
+
+    `None` (type unlodged) defaults to `gable_wall` (party) — the modal
+    RR gable and the conservative choice (party billing at U=0.25 vs the
+    main-wall U). A lodged integer outside the known set raises
+    `UnmappedApiCode` so a new gable variant forces an explicit mapping
+    rather than silently mis-routing its U-value (mirror of the strict-
+    raise pattern on the other API helpers)."""
+    if gable_type is None:
+        return "gable_wall"
+    if gable_type not in _API_TYPE_1_GABLE_TYPE_TO_KIND:
+        raise UnmappedApiCode("gable_wall_type", gable_type)
+    return _API_TYPE_1_GABLE_TYPE_TO_KIND[gable_type]
+
+
+def _api_type_1_gable_surfaces(
+    type_1: Any,
+) -> Optional[List[SapRoomInRoofSurface]]:
+    """Translate the Simplified Type 1 scalar gable fields into the
+    per-surface list the cascade's Detailed-RR branch consumes.
+
+    Gable area = L × the §3.9.1 default RR storey height (2.45 m); the
+    `gable_wall_type_*` code routes the kind (Exposed vs Party). U-values
+    are left to the cascade (Exposed falls through to the main-wall U;
+    Party uses the fixed 0.25). Returns None when no gable length is
+    lodged so the cascade keeps its existing residual-only behaviour."""
+    surfaces: List[SapRoomInRoofSurface] = []
+    for gable_type, length in (
+        (type_1.gable_wall_type_1, type_1.gable_wall_length_1),
+        (type_1.gable_wall_type_2, type_1.gable_wall_length_2),
+    ):
+        if length is None or length <= 0:
+            continue
+        surfaces.append(
+            SapRoomInRoofSurface(
+                kind=_api_type_1_gable_kind(gable_type),
+                area_m2=_round_half_up_2dp(
+                    float(length), _RIR_TYPE_1_GABLE_HEIGHT_M
+                ),
+            )
+        )
+    return surfaces or None
+
+
 def _api_build_room_in_roof(
     bp_rir: Any, *, is_flat: bool = False,
 ) -> Optional[SapRoomInRoof]:
     """Build `SapRoomInRoof` from the API schema's per-bp RR block. Two
     real-API shapes coexist:
       - `room_in_roof_type_1` (cohort certs 6035, 0240): RdSAP §3.9.1
-        Simplified Type 1 — gable lengths only, cascade applies the
-        2.45 m default storey height.
+        Simplified Type 1 — gable lengths only (no heights). Built into
+        `detailed_surfaces` using the 2.45 m default RR storey height so
+        the cascade's residual deducts the gables from the A_RR shell.
       - `room_in_roof_details` (cert 9501): RdSAP §3.9 Detailed RR —
         per-surface lengths + heights + flat-ceiling detail.
-    When the Detailed block is present, build `detailed_surfaces` so the
-    cascade's per-surface RR branch (heat_transmission.py:629) picks
-    up exact gable + flat-ceiling areas instead of falling through to
-    the Table 18 col(4) "all elements" default U.
+    For BOTH shapes we build `detailed_surfaces` so the cascade's
+    per-surface RR branch picks up exact gable + flat-ceiling areas and
+    the §3.9.1(e) residual roof (A_RR shell − Σ gables), instead of
+    billing the whole shell at the Table 18 col(4) "all elements" U.
     """
     if bp_rir is None:
         return None
@@ -2733,10 +3094,20 @@ def _api_build_room_in_roof(
     )
     type_1 = getattr(bp_rir, "room_in_roof_type_1", None)
     if type_1 is not None:
-        # RdSAP §3.9.1 Simplified Type 1: gable lengths only (no heights —
-        # the cascade applies the 2.45 m default storey height).
+        # RdSAP §3.9.1 Simplified Type 1: gable lengths only (no heights).
         rir.gable_1_length_m = type_1.gable_wall_length_1
         rir.gable_2_length_m = type_1.gable_wall_length_2
+        # Route the gables through `detailed_surfaces` so the cascade's
+        # Detailed-RR residual deducts each gable from the A_RR shell
+        # (RdSAP 10 §3.9.1(e) p.21: A_RR_final = 12.5√(A_RR_floor/1.5) −
+        # Σ gables) — the same path the site-notes mapper builds. The
+        # scalar `gable_*_length_m` fields alone can't trigger this: the
+        # cascade's `_part_geometry` gable formula needs a height and
+        # silently drops height-less gables, billing the WHOLE shell as
+        # roof (a ~52 W/K over-count on cert 6035). Gable area = L × the
+        # §3.9.1 default RR storey height (2.45 m); the type code routes
+        # the U-value (Exposed → main-wall U, Party → 0.25).
+        rir.detailed_surfaces = _api_type_1_gable_surfaces(type_1)
     details = getattr(bp_rir, "room_in_roof_details", None)
     if details is not None:
         rir.detailed_surfaces = _api_rir_detailed_surfaces(details, is_flat=is_flat)
@@ -2798,6 +3169,31 @@ def _parse_rir_insulation_thickness_mm(value: Any) -> Optional[int]:
     return int(m.group(1)) if m else None
 
 
+def _api_resolve_wall_insulation_thickness(
+    wall_insulation_thickness: Union[str, int, None],
+    wall_insulation_thickness_measured: Union[str, int, None],
+) -> Union[str, int, None]:
+    """Resolve the wall insulation thickness for the cascade.
+
+    When the cert lodges `wall_insulation_thickness == "measured"` the
+    actual value sits in the separate `wall_insulation_thickness_measured`
+    field (mm). RdSAP 10 §5.7/Table 8 use the measured thickness to pick
+    the insulated-wall U-value row; without it the cascade falls back to
+    the 50 mm "insulation present, unknown thickness" default (e.g. cert
+    2130 Ext1: solid brick band B + internal insulation lodged 100 mm →
+    Table 8 U=0.32, not the 50 mm default 0.55).
+
+    Any other lodgement (numeric string, "NI", None) passes through
+    unchanged."""
+    if (
+        isinstance(wall_insulation_thickness, str)
+        and wall_insulation_thickness.strip().lower() == "measured"
+        and wall_insulation_thickness_measured is not None
+    ):
+        return wall_insulation_thickness_measured
+    return wall_insulation_thickness
+
+
 def _api_resolve_sloping_ceiling_thickness(
     roof_construction: Optional[int],
     roof_insulation_thickness: Union[str, int, None],
@@ -3126,6 +3522,7 @@ def _map_elmhurst_building_part(
         identifier=identifier,
         construction_age_band=age_code,
         wall_construction=_elmhurst_wall_construction_int(walls.wall_type),
+        wall_is_basement=_elmhurst_wall_is_basement(walls.wall_type),
         wall_insulation_type=_elmhurst_wall_insulation_int(walls.insulation),
         wall_thickness_measured=not walls.thickness_unknown,
         party_wall_construction=_elmhurst_party_wall_construction_int(walls.party_wall_type),
@@ -3140,6 +3537,7 @@ def _map_elmhurst_building_part(
             if walls.insulation_thickness_mm is not None
             else None
         ),
+        roof_construction=_elmhurst_roof_construction_int(roof.roof_type),
         roof_construction_type=_strip_code(roof.roof_type),
         roof_insulation_location=_strip_code(roof.insulation),
         roof_insulation_thickness=_resolve_sloping_ceiling_thickness(
@@ -3204,6 +3602,7 @@ def _map_elmhurst_alternative_wall(
         wall_thickness_measured="Y" if not a.thickness_unknown else "N",
         wall_insulation_thickness=None,
         wall_thickness_mm=measured_thickness_mm,
+        is_basement=_elmhurst_wall_is_basement(a.wall_type),
     )
 
 
@@ -3416,6 +3815,25 @@ def _map_elmhurst_rir_surface(
     if prefix is None:
         return None
     kind = _RIR_KIND_FROM_NAME_PREFIX[prefix]
+    # RdSAP 10 §3.9.1 (PDF p.21) Simplified assessment: the roof-going
+    # surfaces (slope / flat ceiling / stud wall) are NOT measured — the
+    # Summary lodges placeholder Length/Height cells (e.g. a 40 m ceiling
+    # height, a 32 m slope on a 4.65 m-wide gable). The spec instead
+    # derives one timber-framed "remaining area" from the floor area:
+    #   A_RR       = 12.5 × √(A_RR_floor / 1.5)            §3.9.1(d)
+    #   A_RR_final = A_RR − ΣA_RR_gable/other              §3.9.1(e)
+    # The cascade computes A_RR_final itself (heat_transmission.py — the
+    # `12.5 × √(A_RR_floor / 1.5) − rr_walls_in_a_rr_area` residual),
+    # but ONLY when `detailed_surfaces` carries no roof-going kind
+    # (`has_roof_lodgement` gate). Emitting these placeholder rows flips
+    # that gate and bills their raw L×H as explicit roof area (a 7.5×
+    # heat-loss explosion). Drop them for Simplified so the cascade's
+    # residual formula fires — matching how the API path already handles
+    # the same Simplified RR (scalar gable fields, no roof-going
+    # detailed_surfaces; cert 6035) and the gables-only cert 000565.
+    # Detailed (§3.10) assessments DO measure these surfaces — keep them.
+    if is_simplified and kind in ("slope", "flat_ceiling", "stud_wall"):
+        return None
     u_value_override: Optional[float] = None
     if kind == "gable_wall" and surface.gable_type == "Sheltered":
         kind = "gable_wall_external"
@@ -3688,6 +4106,11 @@ def _is_elmhurst_roof_window(
     """
     if w.glazing_type.startswith("Single"):
         return False
+    # Explicit "Roof of Room" location lodging (simulated case 6): the
+    # surveyor placed the window on the room-in-roof, so it's a rooflight
+    # regardless of BP roof type or U-value.
+    if "roof of room" in (w.location or "").lower():
+        return True
     bp_roof_type = _elmhurst_bp_roof_type(w, survey)
     if bp_roof_type is not None and bp_roof_type.startswith(
         _ELMHURST_BP_ROOF_TYPES_WITH_ROOFLIGHTS
@@ -3703,6 +4126,12 @@ def _is_elmhurst_roof_window(
 # worksheet's (27a) line. The cohort exercises only "Double pre 2002".
 _ELMHURST_ROOF_WINDOW_U_BY_GLAZING: Dict[str, float] = {
     "Double pre 2002": 3.4,
+    # Simulated case 6 rooflights: the Summary lodges the already-inclined
+    # roof-window U=2.30 for DG-2002-2021 glazing (vs 2.00 vertical for the
+    # same glazing on a wall) — the worksheet bills it on (27a) at U_eff
+    # 2.1062 (= 2.30 with the §3.2 R=0.04 curtain transform). Keyed here so
+    # the inclination adjustment isn't double-applied.
+    "Double between 2002 and 2021": 2.30,
 }
 
 
@@ -4421,8 +4850,14 @@ _ELMHURST_CYLINDER_SIZE_LABEL_TO_SAP10: Dict[str, int] = {
 # which SAP 10.2 Table 2 Note 2 treats as factory-applied PU foam).
 # Other labels (Loose Jacket, None) raise `UnmappedElmhurstLabel`
 # until a fixture exercises them.
+# SAP10 cylinder_insulation_type enum: 1 = factory-applied foam,
+# 2 = loose jacket (matching the GOV.UK API codes). SAP 10.2 Table 2
+# Note 1 gives loose jacket a separate, ~2× higher storage-loss factor;
+# the cascade's loose-jacket branch is wired (S0380.224), so "Jacket"
+# resolves to 2 for cross-mapper parity with the API path.
 _ELMHURST_CYLINDER_INSULATION_LABEL_TO_SAP10: Dict[str, int] = {
     "Foam": 1,
+    "Jacket": 2,
 }
 
 
@@ -4644,6 +5079,36 @@ _ELMHURST_GLAZING_LABEL_TO_SAP10: Dict[str, int] = {
     # solar_transmittance=0.72 overrides per worksheet-pinned value.
     "Triple between 2002 and 2021": 9,
     "Secondary": 7,
+    # Elmhurst §11 lodges the full "Secondary glazing" phrase as well as
+    # the bare "Secondary" form — both are SAP 10.2 Table 6b "window with
+    # secondary glazing" (cascade code 7, g_L=0.80, g⊥=0.76). The
+    # RdSAP-21 schema splits secondary glazing by pane emissivity; the
+    # "Normal emissivity" variant is its own code 11 (g_L=0.80, identical
+    # cascade output to 7, kept distinct for the strict-raise audit
+    # trail). Surfaced on the double_glazing/before recommendation
+    # fixture (Summary_001431 §11 Window 9).
+    "Secondary glazing": 7,
+    "Secondary glazing - Normal emissivity": 11,
+    # RdSAP-21 glazed_type 12 "secondary glazing, low emissivity" — the
+    # low-E sibling of code 11. Cascade code 12 carries g_L=0.80 / g⊥=0.76
+    # (identical daylight/solar bucket to 7 and 11; the lodged U/g drive
+    # §3/§6). Mapped symmetrically with the "Normal emissivity" variant so
+    # the whole secondary-glazing family is covered.
+    "Secondary glazing - Low emissivity": 12,
+    # RdSAP-21 row "triple glazing, installed pre-2002" (cascade code 10,
+    # g_L=0.70, g⊥=0.68 — same triple-glazed daylight/solar bucket as the
+    # other triple variants {6, 8, 9, 14}). The lodged manufacturer
+    # U-value / solar_transmittance drive §6; the code only sets g_L.
+    "Triple pre 2002": 10,
+    # Triple glazing of unknown install date → the generic SAP 10.2
+    # Table 6b "triple glazed" row (cascade code 6, g_L=0.70). No
+    # dedicated "triple, unknown date" enum exists; 6 is the correct
+    # triple-glazed bucket.
+    "Triple with unknown install date": 6,
+    # RdSAP-21 row "single glazing, known data" (cascade code 15,
+    # g_L=0.90, g⊥=0.85 — same as plain single glazing). Manufacturer
+    # U/g lodged on WindowTransmissionDetails drive §6.
+    "Single glazing, known data": 15,
 }
 
 _ELMHURST_GLAZING_LABEL_NOISE_PREFIX_RE: Final[re.Pattern[str]] = re.compile(
@@ -4652,6 +5117,18 @@ _ELMHURST_GLAZING_LABEL_NOISE_PREFIX_RE: Final[re.Pattern[str]] = re.compile(
 _ELMHURST_GLAZING_LABEL_NOISE_SUFFIX_RE: Final[re.Pattern[str]] = re.compile(
     r"\s+Summary Information$|\s+Alternative wall.*$"
 )
+# Fallback only: pdftotext wraps the §11 glazing-GAP column ("6 mm" /
+# "12 mm" / "16 mm or more") onto the glazing-TYPE token on hand-entered
+# worksheets, e.g. "Double between 2002 and 2021 16 mm or [1st]". When the
+# lightly-cleaned label isn't a known key, strip the trailing gap
+# descriptor (and any building-part fragment after it) and retry. Applied
+# AFTER the direct lookup so explicitly-mapped interleaved variants (e.g.
+# "Double with unknown 16 mm or install date more") are unaffected. The
+# gap drives the API-path U-value lookup, not the site-notes glazing-type
+# enum, so dropping it here is loss-free for the cascade.
+_ELMHURST_GLAZING_LABEL_TRAILING_GAP_RE: Final[re.Pattern[str]] = re.compile(
+    r"\s+\d+\s*mm\b.*$"
+)
 
 
 def _elmhurst_glazing_type_code(label: Optional[str]) -> int:
@@ -4668,9 +5145,15 @@ def _elmhurst_glazing_type_code(label: Optional[str]) -> int:
     cleaned = _ELMHURST_GLAZING_LABEL_NOISE_PREFIX_RE.sub("", label)
     cleaned = _ELMHURST_GLAZING_LABEL_NOISE_SUFFIX_RE.sub("", cleaned).strip()
     code = _ELMHURST_GLAZING_LABEL_TO_SAP10.get(cleaned)
-    if code is None:
-        raise UnmappedElmhurstLabel("glazing_type", label)
-    return code
+    if code is not None:
+        return code
+    # Fallback: strip a trailing wrapped glazing-gap descriptor and retry.
+    degapped = _ELMHURST_GLAZING_LABEL_TRAILING_GAP_RE.sub("", cleaned).strip()
+    if degapped != cleaned:
+        code = _ELMHURST_GLAZING_LABEL_TO_SAP10.get(degapped)
+        if code is not None:
+            return code
+    raise UnmappedElmhurstLabel("glazing_type", label)
 
 
 def _elmhurst_main_heating_category(
@@ -4701,6 +5184,10 @@ def _elmhurst_main_heating_category(
 
 def _map_elmhurst_main_heating_2(
     mh2: Optional[ElmhurstMainHeating2],
+    *,
+    fallback_fuel_type: Union[int, str, None] = None,
+    main_floor: Optional[ElmhurstFloorDetails] = None,
+    main_age_band: Optional[str] = None,
 ) -> Optional[MainHeatingDetail]:
     """Build a `MainHeatingDetail` from the Elmhurst §14.1 Main Heating2
     block. Returns None when no Main 2 is lodged (extractor convention:
@@ -4736,25 +5223,51 @@ def _map_elmhurst_main_heating_2(
         and mh2.main_heating_sap_code in _ELECTRIC_SAP_MAIN_HEATING_CODES
     ):
         main_fuel_int = _STANDARD_ELECTRICITY_FUEL_CODE
+    # §14.1 Main Heating2 often omits the "Fuel Type" cell when the
+    # second main system shares Main 1's fuel (simulated case 6: one oil
+    # boiler feeding radiators + underfloor, so the Summary lodges the
+    # fuel once on §14.0). Inherit Main 1's resolved fuel so the §9a
+    # two-main split (213)m can apply system 2's own efficiency.
+    resolved_fuel: Union[int, str] = (
+        main_fuel_int
+        if main_fuel_int is not None
+        else (
+            fallback_fuel_type
+            if (not mh2.fuel_type and fallback_fuel_type is not None)
+            else mh2.fuel_type
+        )
+    )
     category: Optional[int] = None
     if pcdb_index is not None and heat_pump_record(pcdb_index) is not None:
         category = _ELMHURST_HEATING_CATEGORY_HEAT_PUMP
     elif pcdb_index is not None and mh2.fuel_type in _ELMHURST_GAS_BOILER_FUEL_TYPES:
         category = _ELMHURST_HEATING_CATEGORY_GAS_BOILER
+    # §14.1 lodges Main 2's own "Heat Emitter" + "Main Heating Controls
+    # Sap" when the two systems heat different parts of the dwelling
+    # (simulated case 6: Main 1 radiators / 2106, Main 2 underfloor /
+    # 2110). Map them through the same helpers as Main 1 so the SAP 10.2
+    # p.186 two-systems-different-parts MIT can read system 2's
+    # responsiveness (underfloor → emitter 2 → R=0.75) + control type.
+    # Empty-string sentinels preserved for the legacy DHW-only Main 2
+    # (cert 000565: §14.1 omits emitter/control → consumers key off
+    # Main 1).
+    emitter_int = _elmhurst_heat_emitter_int(
+        mh2.heat_emitter, main_floor=main_floor, main_age_band=main_age_band
+    )
+    control_int = _elmhurst_sap_control_code(mh2.heating_controls_sap)
     return MainHeatingDetail(
         # Main 2 doesn't carry its own FGHRS lodgement in §14.1; the
         # cert-level renewables block is the single source of truth and
         # is already wired into Main 1.
         has_fghrs=False,
-        main_fuel_type=main_fuel_int if main_fuel_int is not None else mh2.fuel_type,
-        # §14.1 doesn't lodge a heat emitter (the emitter is Main 1's
-        # radiator/UFH); leave as empty-string sentinel for cascade
-        # consumers that key off Main 1's emitter.
-        heat_emitter_type="",
+        main_fuel_type=resolved_fuel,
+        heat_emitter_type=(
+            emitter_int if emitter_int is not None else mh2.heat_emitter
+        ),
         emitter_temperature="",
         fan_flue_present=mh2.fan_assisted_flue,
         boiler_flue_type=_elmhurst_flue_type_int(mh2.flue_type),
-        main_heating_control="",
+        main_heating_control=control_int if control_int is not None else "",
         main_heating_category=category,
         main_heating_number=2,
         main_heating_fraction=mh2.percentage_of_heat,
@@ -4950,7 +5463,12 @@ def _map_elmhurst_sap_heating(survey: ElmhurstSiteNotes) -> SapHeating:
     # services DHW via `Water Heating SapCode 914` ("from second main
     # system") while Main 1 handles space heat. None when the §14.1
     # block is absent or lodges only placeholder zeros.
-    main_2_detail = _map_elmhurst_main_heating_2(mh.main_heating_2)
+    main_2_detail = _map_elmhurst_main_heating_2(
+        mh.main_heating_2,
+        fallback_fuel_type=main_1_detail.main_fuel_type,
+        main_floor=survey.floor,
+        main_age_band=survey.construction_age_band,
+    )
     main_heating_details = (
         [main_1_detail, main_2_detail]
         if main_2_detail is not None

datatypes/epc/domain/tests/test_from_rdsap_schema.py

@@ -697,3 +697,246 @@ class TestFromRdSapSchema21_0_1:
         assert rhi.impact_of_cavity_insulation_kwh == -122.0
         assert rhi.impact_of_solid_wall_insulation_kwh == -3560.0
 
+
+
+# ---------------------------------------------------------------------------
+# Measured wall insulation thickness (`wall_insulation_thickness == "measured"`)
+# ---------------------------------------------------------------------------
+
+
+class TestApiResolveWallInsulationThickness:
+    """`wall_insulation_thickness == "measured"` resolves to the separate
+    `wall_insulation_thickness_measured` field (previously dropped by
+    `from_dict`, leaving the cascade on the 50 mm unknown-thickness
+    default). Cert 2130 Ext1 lodges solid brick band B + internal
+    insulation "measured"/100 mm → RdSAP 10 Table 8 U=0.32, not 0.55."""
+
+    def test_measured_string_resolves_to_measured_value(self) -> None:
+        # Arrange
+        from datatypes.epc.domain.mapper import (
+            _api_resolve_wall_insulation_thickness,
+        )
+
+        lodged_thickness = "measured"
+        measured_value_mm = 100
+
+        # Act
+        resolved = _api_resolve_wall_insulation_thickness(
+            lodged_thickness, measured_value_mm
+        )
+
+        # Assert
+        assert resolved == measured_value_mm
+
+    def test_non_measured_lodgement_passes_through_unchanged(self) -> None:
+        # Arrange
+        from datatypes.epc.domain.mapper import (
+            _api_resolve_wall_insulation_thickness,
+        )
+
+        ni_lodgement = "NI"
+        measured_value_mm = 100
+
+        # Act
+        ni: object = _api_resolve_wall_insulation_thickness(
+            ni_lodgement, measured_value_mm
+        )
+        none_thk: object = _api_resolve_wall_insulation_thickness(None, None)
+
+        # Assert
+        assert ni == ni_lodgement
+        assert none_thk is None
+
+    def test_measured_without_value_passes_through(self) -> None:
+        # Arrange
+        from datatypes.epc.domain.mapper import (
+            _api_resolve_wall_insulation_thickness,
+        )
+
+        lodged_thickness = "measured"
+        measured_value_mm = None
+
+        # Act
+        resolved: object = _api_resolve_wall_insulation_thickness(
+            lodged_thickness, measured_value_mm
+        )
+
+        # Assert
+        assert resolved == lodged_thickness
+
+
+# ---------------------------------------------------------------------------
+# Glazing-type label cleaning — pdftotext gap-column wrap
+# ---------------------------------------------------------------------------
+
+
+class TestElmhurstGlazingTypeWrappedGap:
+    """When a hand-entered Elmhurst worksheet is dumped via pdftotext, the
+    glazing-GAP column ("16 mm or more") wraps onto the glazing-TYPE token,
+    yielding labels like "Double between 2002 and 2021 16 mm or" (plus a
+    trailing building-part fragment). The extractor must strip the trailing
+    gap descriptor and map the clean type, not raise UnmappedElmhurstLabel."""
+
+    def test_trailing_gap_descriptor_stripped(self) -> None:
+        # Arrange
+        from datatypes.epc.domain.mapper import _elmhurst_glazing_type_code
+
+        # Act
+        code = _elmhurst_glazing_type_code(
+            "Double between 2002 and 2021 16 mm or"
+        )
+
+        # Assert — clean "Double between 2002 and 2021" → SAP10 code 3
+        assert code == 3
+
+    def test_trailing_gap_plus_building_part_fragment_stripped(self) -> None:
+        # Arrange
+        from datatypes.epc.domain.mapper import _elmhurst_glazing_type_code
+
+        # Act
+        code = _elmhurst_glazing_type_code(
+            "Double between 2002 and 2021 16 mm or 1st"
+        )
+
+        # Assert
+        assert code == 3
+
+    def test_clean_label_still_maps(self) -> None:
+        # Arrange — regression guard: an un-wrapped label is unaffected.
+        from datatypes.epc.domain.mapper import _elmhurst_glazing_type_code
+
+        # Act
+        code = _elmhurst_glazing_type_code("Double pre 2002")
+
+        # Assert
+        assert code == 2
+
+
+class TestApiFloorConstructionCode:
+    """`_api_floor_construction_str` maps the GOV.UK API integer
+    floor_construction code to the description string the cascade's
+    `u_floor` + the §5 (12) infiltration rule read. RdSAP 10 field 3-1
+    "Floor construction" enumerates the lowest-floor construction as one
+    of: solid / suspended timber / suspended, not timber. The spec's
+    "Suspended not timber (structural infiltration 0)" makes the
+    timber/not-timber split load-bearing: only "Suspended timber"
+    triggers the §5 (12) 0.1/0.2 floor-infiltration adjustment;
+    "suspended, not timber" is structural-infiltration 0."""
+
+    def test_code_3_maps_to_suspended_not_timber(self) -> None:
+        # Arrange
+        from datatypes.epc.domain.mapper import _api_floor_construction_str  # pyright: ignore[reportPrivateUsage]
+
+        # Act
+        result = _api_floor_construction_str(3)
+
+        # Assert — suspended U-value branch fires (starts "Suspended"),
+        # but the exact-match "Suspended timber" (12) rule does NOT —
+        # per RdSAP 10 "suspended not timber (structural infiltration 0)".
+        # Same canonical string the site-notes mapper already uses.
+        assert result == "Suspended, not timber"
+
+    def test_code_2_still_maps_to_suspended_timber(self) -> None:
+        # Arrange — regression guard: the timber code is unchanged.
+        from datatypes.epc.domain.mapper import _api_floor_construction_str  # pyright: ignore[reportPrivateUsage]
+
+        # Act
+        result = _api_floor_construction_str(2)
+
+        # Assert
+        assert result == "Suspended timber"
+
+    def test_code_0_maps_to_none_unknown_construction(self) -> None:
+        # Arrange — code 0 is the "not recorded / not applicable"
+        # sentinel: it pairs overwhelmingly with floor_heat_loss=6
+        # ("another dwelling below", an upper-floor flat with no ground
+        # floor to describe), but also appears with mixed Solid / unheated
+        # descriptions. There is no single construction to assert, so it
+        # maps to None — RdSAP 10 Table 19 ("where floor construction is
+        # unknown" → age-band default), the same treatment as an unlodged
+        # floor_construction. Empirically inert: floor W/K is identical to
+        # any explicit construction string across all observed code-0
+        # certs (the heat loss is governed by floor_heat_loss, not this).
+        from datatypes.epc.domain.mapper import _api_floor_construction_str  # pyright: ignore[reportPrivateUsage]
+
+        # Act
+        result = _api_floor_construction_str(0)
+
+        # Assert — no raise; None defers to the cascade's Table 19 default.
+        assert result is None
+
+
+class TestDefaultMissingPostTown:
+    """`_default_missing_post_town` keeps a cert mappable when the
+    register omits the required `post_town` field (observed on a 2026
+    cert whose town sits only in address_line_3). post_town is address
+    metadata the SAP cascade never reads, so defaulting it to "" before
+    `from_dict` is inert for the calculation."""
+
+    def test_absent_post_town_is_defaulted_to_empty_string(self) -> None:
+        # Arrange
+        from datatypes.epc.domain.mapper import _default_missing_post_town  # pyright: ignore[reportPrivateUsage]
+        doc: dict[str, object] = {"postcode": "EX31 2LE"}
+
+        # Act
+        result = _default_missing_post_town(doc)
+
+        # Assert
+        assert result["post_town"] == ""
+
+    def test_present_post_town_is_untouched(self) -> None:
+        # Arrange — regression guard: a lodged town passes through.
+        from datatypes.epc.domain.mapper import _default_missing_post_town  # pyright: ignore[reportPrivateUsage]
+        doc: dict[str, object] = {"post_town": "BARNSTAPLE"}
+
+        # Act
+        result = _default_missing_post_town(doc)
+
+        # Assert
+        assert result["post_town"] == "BARNSTAPLE"
+
+
+class TestApiRoofConstructionCode:
+    """`_api_roof_construction_str` maps the GOV.UK API integer
+    roof_construction code to the string the cascade reads ONLY for the
+    "sloping ceiling" cos(30°) inclined-surface factor (Slice 89). Codes
+    6 and 7 are neither sloping ceilings nor base-U drivers (the roof
+    U-value comes from the global roofs[].description), so both map to
+    None: code 6 = "Thatched" (its U is set by the description, not this
+    field) and code 7 = "(same/another dwelling above)" — an internal
+    ceiling with no roof heat loss, the roof-side analogue of
+    floor_construction code 0. Empirically inert: roof W/K is identical
+    whether 6/7 map to None or to an explicit pitched string across all
+    code-6/7 certs in the 2026 sample."""
+
+    def test_code_7_same_dwelling_above_maps_to_none(self) -> None:
+        # Arrange
+        from datatypes.epc.domain.mapper import _api_roof_construction_str  # pyright: ignore[reportPrivateUsage]
+
+        # Act
+        result = _api_roof_construction_str(7)
+
+        # Assert — None: no sloping-ceiling signal (avoids the cos(30°)
+        # false-trigger); the internal ceiling has no roof heat loss.
+        assert result is None
+
+    def test_code_6_thatched_maps_to_none(self) -> None:
+        # Arrange
+        from datatypes.epc.domain.mapper import _api_roof_construction_str  # pyright: ignore[reportPrivateUsage]
+
+        # Act
+        result = _api_roof_construction_str(6)
+
+        # Assert — None: thatched is not a sloping ceiling; its U-value is
+        # carried by the global roof description, not roof_construction_type.
+        assert result is None
+
+    def test_code_8_still_maps_to_sloping_ceiling(self) -> None:
+        # Arrange — regression guard: the sloping-ceiling code is unchanged.
+        from datatypes.epc.domain.mapper import _api_roof_construction_str  # pyright: ignore[reportPrivateUsage]
+
+        # Act
+        result = _api_roof_construction_str(8)
+
+        # Assert
+        assert result == "Pitched, sloping ceiling"

datatypes/epc/schema/rdsap_schema_21_0_0.py

@@ -133,6 +133,7 @@ class SapEnergySource:
     wind_turbines_terrain_type: int
     electricity_smart_meter_present: str
     pv_batteries: Optional[PvBatteries] = None
+    pv_diverter: Optional[str] = None
 
 
 @dataclass
@@ -175,10 +176,11 @@ class SapFloorDimension:
 class RoomInRoofType1:
     """RdSAP §3.9.1 Simplified Type 1 RR — gable lengths only.
 
-    `gable_wall_type_*` is the Table 4 gable variant (0 = external, etc.;
-    full enum not yet mapped). `gable_wall_length_*` is the run of the
-    external gable in metres. Heights are NOT lodged here — the cascade
-    applies the §3.9.1 default storey height (2.45 m)."""
+    `gable_wall_type_*` is the Table 4 gable variant (0 = Party,
+    1 = Exposed — established from cert 6035's Summary; other variants
+    not yet seen). `gable_wall_length_*` is the run of the gable in
+    metres. Heights are NOT lodged here — the mapper applies the §3.9.1
+    default RR storey height (2.45 m)."""
     gable_wall_type_1: Optional[int] = None
     gable_wall_type_2: Optional[int] = None
     gable_wall_length_1: Optional[float] = None
@@ -240,6 +242,16 @@ class SapBuildingPart:
     sap_alternative_wall_2: Optional[SapAlternativeWall] = None
     wall_thickness: Optional[int] = None
     wall_insulation_thickness: Optional[str] = None
+    # Lodged measured insulation thickness (mm) backing a
+    # `wall_insulation_thickness == "measured"` lodgement. Previously
+    # undeclared, so `from_dict` silently dropped it and the cascade fell
+    # back to the 50 mm "insulation present, unknown thickness" default.
+    wall_insulation_thickness_measured: Optional[Union[str, int]] = None
+    # Lodged thermal-conductivity code for measured wall insulation
+    # (RdSAP 10 §5.8: λ = 0.04 / 0.03 / 0.025 W/m·K). Previously undeclared
+    # → dropped by `from_dict`. Consumed by `u_wall`'s documentary-evidence
+    # R-value path when a measured wall thickness is also lodged.
+    wall_insulation_thermal_conductivity: Optional[Union[str, int]] = None
     floor_insulation_thickness: Optional[str] = None
     flat_roof_insulation_thickness: Optional[Union[str, int]] = None
 

datatypes/epc/schema/rdsap_schema_21_0_1.py

@@ -161,6 +161,7 @@ class SapEnergySource:
     wind_turbines_terrain_type: int
     electricity_smart_meter_present: str
     pv_battery_count: Optional[int] = None
+    pv_diverter: Optional[str] = None
     wind_turbine_details: Optional[WindTurbineDetails] = None
     pv_batteries: Optional[Union[PvBatteries, List[PvBatteries]]] = None
 
@@ -207,10 +208,11 @@ class SapFloorDimension:
 class RoomInRoofType1:
     """RdSAP §3.9.1 Simplified Type 1 RR — gable lengths only.
 
-    `gable_wall_type_*` is the Table 4 gable variant (0 = external, etc.;
-    full enum not yet mapped). `gable_wall_length_*` is the run of the
-    external gable in metres. Heights are NOT lodged here — the cascade
-    applies the §3.9.1 default storey height (2.45 m)."""
+    `gable_wall_type_*` is the Table 4 gable variant (0 = Party,
+    1 = Exposed — established from cert 6035's Summary; other variants
+    not yet seen). `gable_wall_length_*` is the run of the gable in
+    metres. Heights are NOT lodged here — the mapper applies the §3.9.1
+    default RR storey height (2.45 m)."""
     gable_wall_type_1: Optional[int] = None
     gable_wall_type_2: Optional[int] = None
     gable_wall_length_1: Optional[float] = None
@@ -278,6 +280,16 @@ class SapBuildingPart:
     sap_alternative_wall_2: Optional[SapAlternativeWall] = None
     wall_thickness: Optional[int] = None
     wall_insulation_thickness: Optional[str] = None
+    # Lodged measured insulation thickness (mm) backing a
+    # `wall_insulation_thickness == "measured"` lodgement. Previously
+    # undeclared, so `from_dict` silently dropped it and the cascade fell
+    # back to the 50 mm "insulation present, unknown thickness" default.
+    wall_insulation_thickness_measured: Optional[Union[str, int]] = None
+    # Lodged thermal-conductivity code for measured wall insulation
+    # (RdSAP 10 §5.8: λ = 0.04 / 0.03 / 0.025 W/m·K). Previously undeclared
+    # → dropped by `from_dict`. Consumed by `u_wall`'s documentary-evidence
+    # R-value path when a measured wall thickness is also lodged.
+    wall_insulation_thermal_conductivity: Optional[Union[str, int]] = None
     floor_insulation_thickness: Optional[str] = None
     flat_roof_insulation_thickness: Optional[Union[str, int]] = None
 

datatypes/epc/surveys/elmhurst_site_notes.py

@@ -244,6 +244,15 @@ class MainHeating2:
     fan_assisted_flue: bool = False
     percentage_of_heat: int = 0
     main_heating_sap_code: Optional[int] = None
+    # §14.1 "Heat Emitter" (e.g. "Underfloor Heating") + "Main Heating
+    # Controls Sap" (e.g. "SAP code 2110, ..."). Lodged when the two main
+    # systems serve different parts of the dwelling with their own
+    # emitter + control (simulated case 6: Main 1 radiators / control
+    # 2106, Main 2 underfloor / control 2110). Needed for the SAP 10.2
+    # p.186 two-systems-different-parts MIT (weighted responsiveness +
+    # elsewhere two-control blend).
+    heat_emitter: str = ""
+    heating_controls_sap: str = ""
 
 
 @dataclass
@@ -409,6 +418,11 @@ class Renewables:
     solar_hw_collector_orientation: Optional[str] = None
     solar_hw_collector_pitch_deg: Optional[int] = None
     solar_hw_overshading: Optional[str] = None
+    # Summary §19.0 "Diverter present" — a PV diverter routes surplus PV
+    # generation to an immersion heater in the hot-water cylinder
+    # (SAP 10.2 Appendix G4). Drives worksheet (63b)m. Defaults False
+    # when the cert lodges no PV or "Diverter present = No".
+    pv_diverter_present: bool = False
 
 
 @dataclass

docs/PR_NOTE_system_built_basement_1177.md

@@ -0,0 +1,62 @@
+# PR note — SY system-built vs B basement wall (issue #1177)
+
+For the reviewer / the `feature/bill-derivation` session. Fold the relevant
+parts into the PR description; delete this file before/at merge.
+
+## What this branch changed (commit `bd25a3c7`)
+
+`wall_construction == 6` (`WALL_SYSTEM_BUILT`) is the canonical **wall type**
+for system-built — and it stays there. The basement signal, which had hijacked
+code 6, is moved onto a dedicated flag:
+
+- `SapBuildingPart.wall_is_basement: Optional[bool]` and
+  `SapAlternativeWall.is_basement: Optional[bool]`.
+- `main_wall_is_basement` / `is_basement_wall` honour the flag when set, else
+  fall back to the legacy `wall_construction == 6` heuristic (so untouched API
+  basements and the cert 000565 "B" cohort are unchanged).
+- Elmhurst: `_elmhurst_wall_is_basement` sets the flag from the distinct
+  "SY"/"B" labels (SY→False, B→True, other→None).
+- gov-EPC API: `from_api_response` post-processes via
+  `_clear_basement_flag_when_system_built` — when the cert `addendum.system_build`
+  is True, the code-6 basement heuristic is cleared.
+- `EpcPropertyData.system_build` is a **derived `@property`** (not a stored
+  field): the MAIN wall is system-built iff `wall_construction == 6` and it is
+  not flagged basement. (Per the call: "system build is the wall type and
+  should be on `wall_construction`.")
+
+Acceptance verified: system-built main wall → `wall_construction == 6`,
+`main_wall_is_basement is False`, `system_build is True`; genuine basement main
+wall → `main_wall_is_basement is True`, `system_build is False`. Full §4 suite
+green (2404 passed), zero new pyright errors.
+
+## ⚠️ Merge collision: `system_build` field (yours) vs property (this branch)
+
+The `#1177` prompt referenced `EpcPropertyData.system_build` as an existing
+**field** on `feature/bill-derivation`. This branch adds `system_build` as a
+**`@property`**. They share the name but live in different regions of the class,
+so:
+
+- **Git will likely merge them silently** (no textual conflict).
+- **Python will NOT raise at import** — the class defines fine.
+- It raises `AttributeError: property 'system_build' ... has no setter` at the
+  **first `EpcPropertyData(...)` instantiation** — i.e. the first mapper call,
+  so the test suite fails immediately. (Reproduced.)
+
+So the collision is caught fast but is a landmine, not a clean signal. **Resolve
+it deliberately at merge** — pick ONE representation:
+
+- **Recommended (matches the agreed model):** drop the stored field; keep the
+  derived property (system-built is the wall type). If your code currently
+  *assigns* `epc.system_build = …`, replace those writes with setting the
+  underlying wall type / basement flag, or add a setter.
+- **Or** keep your stored field and delete this branch's property — but then
+  populate the field consistently with the wall type on BOTH paths (API addendum
+  *and* Elmhurst "SY"), so `system_build` and `wall_construction`/the basement
+  flag never disagree.
+
+## Tripwire you own
+
+`tests/domain/modelling/test_elmhurst_cascade_pins.py::test_system_built_generator_offers_ewi_and_iwi_each_pinning_its_after`
+is a strict-xfail on your branch (fixtures `system_built_{ewi,iwi}_001431_{before,after}.pdf`
+are committed there, not here). With this fix the behaviour it guards is
+satisfied, so it should flip xfail→xpass — delete the marker when it does.

docs/migrations/epc-property-round-trip-fidelity.md

@@ -32,8 +32,9 @@ and **still require the matching DB migration** wherever the physical tables liv
   `heating_secondary_heating_type`, `heating_shower_outlet_type`, `energy_pv_connection`;
   `epc_main_heating_detail`: `main_fuel_type`, `heat_emitter_type`, `emitter_temperature`,
   `main_heating_control`; `epc_building_part`: `wall_construction`, `wall_insulation_type`,
-  `party_wall_construction`, `flat_roof_insulation_thickness`, `roof_insulation_location`,
-  `roof_insulation_thickness`; `epc_window`: `glazing_gap`, `orientation`, `window_type`,
+  `party_wall_construction`, `wall_insulation_thickness`, `flat_roof_insulation_thickness`,
+  `roof_insulation_location`, `roof_insulation_thickness`; `epc_window`: `glazing_gap`,
+  `orientation`, `window_type`,
   `glazing_type`, `window_location`, `window_wall_type`, `draught_proofed`,
   `permanent_shutters_present`, `transmission_data_source`).
 - **New scalar columns** — `epc_property`: `heating_number_baths`, `heating_number_baths_wwhrs`,
@@ -68,7 +69,7 @@ in the forward mapper so the Python type round-trips exactly (JSON scalars prese
 |---|---|
 | `epc_property` | `heating_cylinder_size`, `heating_immersion_heating_type`, `heating_cylinder_insulation_type`, `heating_secondary_heating_type`, `heating_shower_outlet_type`, `energy_pv_connection` |
 | `epc_main_heating_detail` | `main_fuel_type`, `heat_emitter_type`, `emitter_temperature`, `main_heating_control` |
-| `epc_building_part` | `wall_construction`, `wall_insulation_type`, `party_wall_construction`, `flat_roof_insulation_thickness`, `roof_insulation_location`, `roof_insulation_thickness` |
+| `epc_building_part` | `wall_construction`, `wall_insulation_type`, `party_wall_construction`, `wall_insulation_thickness`, `flat_roof_insulation_thickness`, `roof_insulation_location`, `roof_insulation_thickness` |
 | `epc_window` | `glazing_gap`, `orientation`, `window_type`, `glazing_type`, `window_location`, `window_wall_type`, `draught_proofed`, `permanent_shutters_present` |
 
 (`energy_meter_type` and `energy_wind_turbines_terrain_type` are `str` in the domain — leave as

domain/sap10_calculator/calculator.py

@@ -425,9 +425,15 @@ def _solve_month(
     # SAP 10.2 §8 — (98c)m precomputed upstream by `space_heating_monthly_kwh`
     # (includes Table 9c summer clamp Jun..Sep). Calculator indexes directly.
     q_heat = inputs.space_heating_monthly_kwh[month - 1]
-    # SAP 10.2 §9a — (211)m/(215)m precomputed upstream by
+    # SAP 10.2 §9a — (211)m/(213)m/(215)m precomputed upstream by
     # `space_heating_fuel_monthly_kwh`. Calculator stops doing q/η inline.
-    fuel_main = inputs.energy_requirements.main_1_fuel_monthly_kwh[month - 1]
+    # `main_heating_fuel_kwh` aggregates both main systems (213)m is zero
+    # for single-main certs, so this is the per-system sum for dual-main
+    # dwellings (cert 0240 / simulated case 6) and main-1 alone otherwise.
+    fuel_main = (
+        inputs.energy_requirements.main_1_fuel_monthly_kwh[month - 1]
+        + inputs.energy_requirements.main_2_fuel_monthly_kwh[month - 1]
+    )
     fuel_secondary = inputs.energy_requirements.secondary_fuel_monthly_kwh[month - 1]
 
     # SAP 10.2 §8c — (107)m precomputed upstream by `space_cooling_monthly_kwh`

domain/sap10_calculator/docs/HANDOVER_0240_CLOSURE.md

@@ -0,0 +1,212 @@
+# Handover — closing golden cert 0240-0200-5706-2365-8010 to 1e-4
+
+Point-in-time note. Start from [`AGENT_GUIDE.md`](AGENT_GUIDE.md) for methodology,
+accuracy bar, and pipeline. This records the state of cert **0240** and the
+concrete path to driving its residual to zero.
+
+- **Branch:** `feature/per-cert-mapper-validation`
+- **HEAD:** `7344f600` (S0380.207). Confirm with `git rev-parse HEAD`.
+- **Baseline:** `2372 passed, 1 skipped, 0 failed` (AGENT_GUIDE §4 suite command).
+
+---
+
+## What the last session shipped (S0380.201–207)
+
+Closed **simulated case 6** (`001431_case6`) to 1e-4 on the full SapResult and
+promoted it to an e2e fixture. It is the worksheet-backed proxy for 0240's
+**dual-oil, different-parts** archetype (Main 1 rads/2106 + Main 2 UFH/2110,
+51/49, 6 "Roof of Room" rooflights, no boiler interlock). Slices:
+
+| slice | spec | what |
+|---|---|---|
+| S0380.201 | Table 4f note c) | 2nd-main circulation pump → (231) |
+| S0380.202 | Table 5a note a) | 2nd-main pump **gain** → (70) |
+| S0380.203 | RdSAP §3.7 | "Roof of Room" rooflights deduct from the §3.10.1 RR residual → (30) |
+| S0380.204 | extractor/mapper | capture Main 2's §14.1 emitter + control |
+| S0380.205 | SAP 10.2 **p.186** | two-systems-different-parts MIT: weighted R + elsewhere two-control blend → (87)/(90)/(98c) |
+| S0380.206 | Appendix D Eq D1 | Q_space = DHW boiler's own (204) share, not (202) → (219) |
+| S0380.207 | test | promote case 6 to a full e2e fixture |
+
+**0240 was re-pinned at each step** (it shares the archetype) and its residual
+improved on PE/CO2 but its SAP integer dropped 73→72. The boiler-interlock −5pp
+the *previous* handover called the priority was already implemented — see
+[[project_case6_interlock_already_done]].
+
+---
+
+## The 0240 problem — and why case 6 did NOT close it
+
+### ⚠️ Critical: 0240 is API-only and its register target is INTEGER-rounded
+
+0240 has **no worksheet**. The golden test pins the cascade against the lodged
+EPC register:
+- `energy_consumption_current = 122` — **an integer** (1 kWh/m² resolution).
+- `co2_emissions_current = 6.0` — **1 d.p.** (tonnes).
+- `current_energy_efficiency = None` — the SAP isn't even in the JSON
+  (`actual_sap=73` in the test was carried from the original lodgement).
+
+**You cannot drive 0240 to "0 residual" at 1e-4 against these.** The register
+rounds PE to the nearest whole kWh/m², so any cascade value in `[121.5, 122.5)`
+*is* 122, and the true (unrounded) Elmhurst value could sit anywhere in that band
+— or itself carry residual vs the rounded lodgement. Matching a rounded integer
+to 1e-4 is not a well-posed target. **The only 1e-4 ground truth is a worksheet**
+(the per-line `(1)..(286)` Elmhurst output), which is exactly why case 5/6 were
+generated.
+
+Current 0240 cascade vs lodged: **PE 123.8687 vs 122 (resid +1.8687)**, **CO2
+6.0907 vs 6.0 (+0.0907)**, SAP cont 72.39 (integer 72 vs lodged 73, resid −1).
+
+### Why case 6 didn't close 0240
+
+Case 6 validated the dual-main **structure** (MIT p.186, pumps, rooflights,
+Eq-D1 fraction). But 0240 differs in cert-specific features case 6 does **not**
+exercise:
+
+| feature | case 6 (worksheet-validated) | **0240** (unvalidated) |
+|---|---|---|
+| SAP code | 127 regular oil boiler | **130 condensing oil combi** (Table 4b 82/73) |
+| DHW path | regular boiler **+ 110 L cylinder** → primary/storage loss | **combi, NO cylinder** → Table 3a keep-hot **600 kWh** (`combi_loss`), primary_loss 0 |
+| TFA | (case-6 dwelling) | **201.53 m²** (different fabric/dimensions) |
+| PV | none | **none** (the golden note's "+ PV" is STALE — `solar_water_heating=N`, no PV field) |
+
+So 0240's *remaining* residual lives in the parts case 6 never touched —
+**the condensing-combi (130) + no-cylinder HW path** and the cert's own fabric.
+The combi Eq-D1 / Table 3a keep-hot path has never been pinned against a
+worksheet in the dual-main context.
+
+### Partial ground truth already in the 0240 JSON
+
+The lodged `renewable_heat_incentive` block gives two deemed-demand figures:
+- `water_heating = 2842.82` — **exactly equals** the cascade's §4 HW output
+  `(64)` (2842.82). So the **HW demand is right**; any HW residual is in the
+  *efficiency* (Eq D1 combi blend), not the demand.
+- `space_heating_existing_dwelling = 13254.52` vs cascade `(98c)` 12760.9 —
+  differ ~494 kWh (~3.7%). RHI uses its own deemed methodology so this is **not**
+  a clean 1e-4 check, but it's a hint the space-heat demand or the combi figures
+  are worth scrutinising.
+
+---
+
+## What to do next — generate the right example
+
+To close 0240 properly you need a **worksheet** that exercises its
+combi-HW path. Two options, best first:
+
+1. **Exact 0240 replica worksheet (gold standard).** Re-enter 0240's lodged data
+   into Elmhurst and export the worksheet PDF. Then build a mapper-driven fixture
+   (mirror `_elmhurst_worksheet_001431_case6.py`) and pin every line `(1)..(286)`
+   at 1e-4. The first diverging line localises the residual exactly. This is the
+   only way to get a true 1e-4 target for 0240.
+
+2. **"Case 7" — case 6 with 0240's combi swapped in.** If generating an exact
+   0240 replica is hard, generate a `001431` variant that changes case 6's
+   heating to **0240's**:
+   - **Condensing oil combi, SAP code 130** (not 127 regular boiler).
+   - **NO hot water cylinder** — combi instantaneous DHW → WHC 901, Table 3a/3b
+     combi keep-hot loss, no primary/storage loss.
+   - Keep the validated dual-main rads(2106)+UFH(2110) 51/49 + RR rooflights.
+   This pins the **combi Eq-D1 + Table 3 keep-hot** path (the biggest unvalidated
+   piece) against a worksheet. Whatever it reveals applies directly to 0240.
+
+**The single most important differentiator to change vs case 6: regular
+boiler + cylinder → condensing combi (130) with no cylinder.** That is the one
+HW path 0240 uses that has never seen a worksheet in this archetype.
+
+### Reframing the goal
+If a worksheet is genuinely unavailable, "0 residual vs the lodged register" is
+not achievable at 1e-4 (integer rounding). The realistic target then is the
+**±0.5 SAP fallback** (AGENT_GUIDE §1) — and 0240's continuous SAP 72.39 vs
+lodged 73 is ~0.6 off, just outside it. Closing that last 0.6 still requires
+knowing the true (worksheet) value, so the worksheet is the unblocker either way.
+
+---
+
+## 0240 worksheet input specification (build THIS in Elmhurst)
+
+Reproduce cert **0240-0200-5706-2365-8010** as closely as possible so the
+worksheet is a valid 1e-4 ground truth for the cascade. All values are from the
+fixture JSON (`tests/.../fixtures/golden/0240-0200-5706-2365-8010.json`). Match
+the **U-values / W-per-K targets** below — those are what the cascade actually
+consumes, so hitting them matters more than the exact construction wording.
+
+**Dwelling**
+- Detached house, **construction age band J**, England. Postcode **LE15 9LB**
+  (drives the demand/EPC climate). 1 extension. 7 habitable rooms.
+- Storey height **2.28 m**. Total floor area **≈202 m²** =
+  Main ground floor **97.72** + Extension 1 ground floor **20.61** + the
+  room-in-roof floor **83.2**.
+
+**Heating — the load-bearing difference vs case 6.** TWO main systems, both a
+**condensing oil combi, SAP main heating code 130** (Table 4b winter **82** /
+summer **73**), oil fuel, **balanced flue** (not fan-assisted), efficiency from
+the **SAP table** (no PCDB boiler index), central-heating pump age **unknown**.
+They heat **different parts** (so the p.186 MIT applies, already implemented):
+- **Main 1** — **radiators**, control **2106** (programmer + room thermostat +
+  TRVs), **51%**, serves the living area.
+- **Main 2** — **underfloor heating in screed** (R=0.75), control **2110** (time +
+  temperature zone control), **49%**, serves elsewhere.
+
+**Domestic hot water — the other key difference vs case 6.** Heated **from the
+main system** (WHC 901), oil. It is a **COMBI with NO hot-water cylinder** —
+instantaneous DHW → SAP 10.2 **Table 3a keep-hot loss 600 kWh/yr** (`combi_loss`
+600, `primary_loss` 0). 3 **mixer** showers + 1 bath; no effective WWHRS.
+NB the lodged RHI `water_heating = 2842.82` already equals the cascade HW output
+exactly, so get the DHW *demand* inputs right and any residual is in the combi
+*efficiency* (Eq D1 winter/summer blend).
+- **Boiler interlock: YES** for 0240 (combi + room thermostat 2106, no cylinder)
+  → **no −5pp penalty**, both systems run at base eff 82/73. (This is the
+  OPPOSITE of case 6, which had a regular boiler + cylinder with no cylinder stat
+  → −5pp. Get this right or the efficiencies — hence everything — will be off.)
+
+**Fabric — target W/K (cascade values to reproduce; total external area 328.97 m²):**
+| element | W/K | notes |
+|---|---|---|
+| Walls (29a) | 24.45 | age J, **uninsulated** (NI), not dry-lined, not measured |
+| Roof (30) | 32.331 | Main = pitched, **access to loft**, insulation at ceiling, **400 mm+** ; Ext1 = pitched **vaulted ceiling**, **no insulation (NI)** |
+| Floor (28) | 29.4297 | **solid**; Main heat-loss perimeter 36.45, Ext1 13.45 |
+| Party/gable (32) | 7.84 | RR gables billed as party at U=0.25 |
+| Windows (27) | 22.7407 | see below |
+| Roof windows (27a) | 12.6374 | see below |
+| Doors (26) | 11.1 | **2 doors, uninsulated** |
+| Thermal bridging (36) | 36.1867 | = 0.11 × 328.97 |
+| **(33) fabric total** | **140.5288** | |
+| **(37)+vent feeds (39)** | total transmission **176.7155** | |
+
+**Room-in-roof** (Main only): floor area **83.2 m²**, **two gables L = 6.40 m**
+— one **Exposed**, one **Party** (per the case-5/6 sandstone replica convention),
+age J. This is the same Simplified/detailed-gable RR structure case 6 validated.
+
+**Windows** (all **double glazed, PVC frame**, glazing "DG 2002+", U≈2.0, g=0.72):
+- 5 **vertical** wall windows: 1.4×1.3, 1.2×1.3 (orient N), 1.6×1.3, 2.5×2.0
+  (orient E), 1.4×1.3 (orient S, on Extension 1).
+- 6 **"Roof of Room" rooflights** (window_wall_type 4): all **1.0×1.0**, at 45°,
+  3 orient N + 3 orient S. These bill on (27a) and deduct from the RR residual
+  (S0380.203) — keep them as roof-of-room, not vertical glazing.
+
+**Ventilation / lighting / other**
+- Natural ventilation; **no** mechanical ventilation, **no** extract fans, **no**
+  chimneys/flues. 85% draught-proofed.
+- Lighting: **8 LED bulbs, 100% low-energy** (no CFL/incandescent).
+- **No PV**, no solar thermal, **no secondary heating**, no air-conditioning.
+- Electricity meter type 3 (standard), smart meter present, not export-capable.
+
+### The three things that MUST differ from case 6 (or you've just rebuilt case 6)
+1. **Condensing oil combi, SAP code 130** (case 6 = regular oil boiler 127).
+2. **Combi, NO cylinder** → Table 3a keep-hot 600 kWh (case 6 = boiler + 110 L
+   cylinder → primary/storage loss).
+3. **Boiler interlock PRESENT → no −5pp** (case 6 = no interlock → −5pp). Driven
+   automatically by "combi + room thermostat, no cylinder", but verify the
+   worksheet shows base eff 82/73, not 77/68.
+
+Everything else (dual-main different-parts MIT, two pumps, rooflight→RR, Eq-D1
+(204) share) is already implemented and validated by case 6 — the new worksheet
+just confirms the combi-HW path on top of that closed structure.
+
+---
+
+## Pointers
+- Golden pin + full slice history: `tests/domain/sap10_calculator/rdsap/test_golden_fixtures.py` (cert `0240-0200-5706-2365-8010`, line ~83).
+- Case-6 fixture to mirror: `tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_001431_case6.py` + its e2e pins in `test_e2e_elmhurst_sap_score.py::_FIXTURE_PINS["001431_case6"]`.
+- Memories: [[project_case6_mit_two_system_rootcause]] (the p.186 MIT, now CLOSED), [[project_case6_interlock_already_done]], [[feedback-worksheet-not-api-reference]] (API matches the worksheet, not the lodged register), [[feedback-software-no-special-handling]].
+- Repro 0240: `EpcPropertyDataMapper.from_api_response(json.load(...0240.json))` → `cert_to_inputs` / `cert_to_demand_inputs` → `calculate_sap_from_inputs`. The §2.4 section helpers are UNFAITHFUL (skip the interlock penalty + two-system MIT params) — diagnose against the real `cert_to_inputs` cascade.
+- Process: one slice = one commit, spec citation (page+line), `Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>`. SAP 10.2 only. No tolerance widening. mapper.py + cert_to_inputs.py each carry 32 pre-existing pyright errors (baseline-compare with `git stash`).

domain/sap10_calculator/docs/HANDOVER_API_SAMPLE_ACCURACY.md

@@ -0,0 +1,318 @@
+# Handover — wide-scale API accuracy study + next steps
+
+Point-in-time note. Start from [`AGENT_GUIDE.md`](AGENT_GUIDE.md) for methodology, the
+1e-4 bar, the per-line debugging loop, the section helpers, and the suite command.
+
+- **Branch:** `feature/per-cert-mapper-validation`
+- **HEAD:** `9521d524`. Next SAP slice: **S0380.235**.
+- **Baseline (§4 suite):** `tests/domain/sap10_calculator/ backend/documents_parser/tests/`
+  → green (2412 passed, 1 skipped). Pre-existing out-of-scope failures unchanged
+  (stone-§5.6 in `domain/sap10_ml/tests/`; `test_from_rdsap_schema.py::...test_total_floor_area`).
+
+## Shipped this session (S0380.232-234 — the case-19 PV closure)
+
+The PV diverter (the prior handover's S0380.232 ask) needed two prerequisite
+spec bugs fixed first; all three landed:
+
+| slice | commit | spec | what |
+|---|---|---|---|
+| **S0380.232** | `212b0c92` | App M1 §3a (p.93, l.5470-5476) | D_PV excludes the LOW-rate portion of an off-peak electric main: `(211)` is only PV-eligible where its §10a code ∈ {30,32,34,35,38}. Storage heaters on 7-hr charge wholly at low rate → fraction 0.0 → excluded. β_Jan 0.894→0.792 (ws 0.791). New `_main_space_heating_high_rate_fraction`. |
+| **S0380.233** | `d4a8c02b` | App M1 §6 (p.94, l.5510-5513) | PV-used-in-dwelling credited at the Table 12a ALL_OTHER_USES **weighted** rate (7-hr 14.311 p/kWh), not the bare low rate (5.50). Was under-crediting onsite PV on every off-peak PV cert. Delegates to `_other_fuel_cost_gbp_per_kwh`; STANDARD unchanged. |
+| **S0380.234** | `9521d524` | Appendix G4 (p.72-73) | The PV diverter. 3 layers: extractor `Diverter present` + schema `pv_diverter` → `pv_diverter_present` flag (Elmhurst + API mappers) → `_pv_diverter_monthly_kwh` (SPV = export×0.8×0.9, clamp ≤ (62)+(63a), → (63b)m); `cert_to_inputs` recomputes (219) + PV export, β fixed pre-diverter. |
+
+**Case 19 now: SAP cont 50.33 → 51.34** (ws 51.2221; both round to lodged **51**),
+cost (255) 1847.5→1812.3 (ws 1816.6), CO2 3331→3120 (ws 3126), (233a) dwelling
+1280.6 (ws **1280.4** — the β fix pins it). The diverter formula is **exact in
+summer** (Jun SPV 186.07 = export×0.72, matches ws (63b)).
+
+**The remaining +0.11 SAP on case 19 = two separate, still-open causes:**
+1. **Winter Appendix-M monthly EPV shape.** Our annual EPV (2684.17) matches the
+   worksheet exactly and Jun-Sep match per-month exactly, but Jan-May/Oct-Dec our
+   EPV is ~9-11% LOW (worksheet Jan 68.2 vs ours 62.5). Back-solve: ws EPV_m =
+   |(233a)_m| + |(63b)_m|/0.72. This under-diverts in winter → export (233b) 280.7
+   vs ws 184.2, and (219) 3322 vs ws 3188. **A two-array PV apportionment issue
+   (case 19 has SE + NW arrays with different overshading) — chase in §M / Appendix U
+   monthly radiation, NOT the diverter (which is validated).**
+2. **Fabric (33) +1.0 W/K** (ours 305.04 vs ws 304.04) — a single element off by
+   exactly 1.0; floor=25.000 is suspiciously round. Walk the per-element §3 breakdown.
+
+The **eval headline is flat** (42.9→43.0% <0.5; cat-7 5.25→4.93) — expected: the
+diverter is rare and the β/price effects are small on the rounded SAP. The value
+was pinning the worksheet-validated case 19 + fixing three real spec bugs that the
+curated cohort masked.
+
+## Headline now (1,000-cert 2026 API sample, HEAD `f326e4eb`)
+
+| metric | value | was (handover baseline `9c0a373f`) |
+|---|---|---|
+| computed | 882 / 1000 | 882 |
+| **% \|err\| < 0.5** | **42.9%** | 41.8% |
+| % < 1 / < 2 / < 5 | 56.7% / 74.6% / 90.1% | 54.9 / 71.9 / 87.8 |
+| median / mean \|err\| | 0.73 / **2.04** | 0.79 / ~2.4 |
+| mean signed | −0.41 | +0.2 |
+
+**Error by heating cluster** (the load-bearing cut — re-run `analyse_api_sap_clusters.py`):
+
+| cluster | n | mean \|err\| | %<0.5 | note |
+|---|---|---|---|---|
+| cat 2 gas boiler + PCDB | 639 | 1.27 | 49.6% | well-trodden |
+| cat 2 gas, NO PCDB idx | 91 | 3.18 | 35.2% | non-PCDB Table-4b boilers |
+| cat 6 community | 45 | 2.59 | 31.1% | known-hard |
+| cat 7 electric storage | 40 | **5.25** | 10.0% | was 7.33 → S0380.227-229 |
+| cat 10 electric room heaters | 48 | **5.26** | 16.7% | was 9.49 → S0380.230-231 (bias gone) |
+| cat 4 HP + PCDB | 8 | 6.11 | 12.5% | small n, APM |
+| Flats (any) | 282 | 2.57 | 30.5% | geometry / communal |
+| real PV | 45 | 3.90 | 26.7% | Appendix M |
+
+**Worst individual offenders** (the long tail — `eval` TOP 40): `2100-5421-0922-1622-3463`
+(−60.8, our SAP **negative** −24.8 vs lodged 36 — a flat, 2 bps, cat-2; the single worst, likely
+a geometry/communal blow-up — START a per-cert dig here), `2958-8008` (+32, age 6=tiny),
+`9836-5829` (−29.5, cat-10 tail), several cat-7/cat-10 in the −20s.
+
+## Work shipped (this session — S0380.227-231 + 3 mapper commits)
+
+| commit | what |
+|---|---|
+| **S0380.227** | dedicated DHW-only system (WHS 911) is NOT separately timed → no Table 2b ×0.9; TF (53) 0.54→0.60, (59) h=3→5 |
+| **S0380.228** | electric SECONDARY on off-peak bills at Table 12a `OTHER_DIRECT_ACTING_ELECTRIC` (1.00 high-frac), not 100% low |
+| **S0380.229** | dedicated water boiler/circulator (WHC 911-931) feeds cylinder via primary loop → Table 3 primary loss applies |
+| **S0380.230** | electric room heaters (cat 10) on off-peak → `OTHER_DIRECT_ACTING_ELECTRIC` (mirror of .228 for the MAIN). cat-10 9.49→7.11 |
+| **S0380.231** | Dual-meter electric room heaters → 10-hour tariff (RdSAP §12 Rule 3; codes 691-694,699). cat-10 7.11→5.26, bias +5.08→−0.86 |
+| `bd25a3c7` | SY system-built vs B basement: code 6 stays system-built; basement → explicit `wall_is_basement`/`is_basement` flag. `system_build` is a derived property (wall type). API path post-processes via addendum. (issue #1177 — see `docs/PR_NOTE_system_built_basement_1177.md`: field-vs-property merge landmine) |
+| `f326e4eb` | Elmhurst path now populates `roof_construction` (int) via `_elmhurst_roof_construction_int` for cross-mapper parity (API set it, Elmhurst didn't) |
+- **Toolkit (committed):** `scripts/fetch_2026_epc_sample.py`,
+  `scripts/eval_api_sap_accuracy.py`, `scripts/analyse_api_sap_clusters.py`. The 1,000 cached
+  JSONs live in `/tmp/epc_2026_sample/` (gitignored scratch — re-fetch with the sampler;
+  `EPC_SAMPLE_CACHE` overrides the dir). Re-run the eval after any mapper/calculator change to
+  watch the headline move.
+
+---
+
+## What this study did
+
+Fetched a **random 1,000-cert sample of domestic EPCs lodged Jan–May 2026** from the
+GOV.UK EPB register (the `/api/domestic/search` date-windowed endpoint to enumerate cert
+numbers across random pages → `/api/certificate` per cert for the full schema-21 JSON), ran
+each through the **API path** (`from_api_response → cert_to_inputs → continuous SAP`), and
+compared to the lodged rounded `energy_rating_current`.
+
+**This is the first measurement of raw-API behaviour on an unbiased population** — the curated
+golden cohort (~exact) masked it.
+
+### Reproduce
+- Sampler/fetcher: `/tmp/sample_fetch_2026.py` → caches JSONs to `/tmp/epc_2026_sample/`.
+- Evaluator: `/tmp/eval_sap_accuracy.py` → per-cert CSV + summary (`% <0.5`, buckets, worst-40,
+  raise breakdown). Cluster analysis: `/tmp/analyze2.py`. (Token in `backend/.env`
+  `OPEN_EPC_API_TOKEN`; `date_end` must be < today.)
+- **These scripts are uncommitted (in /tmp).** Worth promoting to `scripts/` if this becomes
+  a recurring measurement.
+
+---
+
+## Headline (at HEAD `9c0a373f`)
+
+| metric | value |
+|---|---|
+| computed | **882 / 1000** (100 unsupported pre-21 schema; 18 still raise) |
+| **% \|err\| < 0.5** (of computed) | **41.8%** |
+| % < 1.0 / < 2.0 / < 5.0 | 54.9% / 71.9% / 87.8% |
+| median / mean \|err\| | 0.79 / ~2.4 |
+| mean signed err | +0.2 (slight over-rate) |
+
+**Accuracy is dominated by heating type** (the load-bearing cut):
+
+| main_heating_category | n | mean \|err\| | %<0.5 | status |
+|---|---|---|---|---|
+| 2 = gas boiler (PCDB-indexed) | 579 | 1.30 | 48% | the well-trodden path |
+| **7 = electric storage heaters** | 39 | **7.33** | **3%** | **broken — #1 lever** |
+| **10 = electric room heaters** | 43 | **10.26** | **9%** | **broken — #2 lever** |
+| 6 = community scheme | 38 | 2.28 | 34% | known-hard |
+| Flats (any heating) | 242 | 3.19 | 29% | geometry + communal |
+
+---
+
+## Work shipped this session (S0380.219–225)
+
+Coverage unblocked **788 → 882 computed (+94)**; one real accuracy bug fixed (+22 certs).
+
+| slice | fix | certs |
+|---|---|---|
+| S0380.219 | floor_construction 3 → "Suspended, not timber" (RdSAP 10 field 3-1) | ~44 |
+| S0380.220 | floor_construction 0 → None (Table 19 unknown; proven inert) | 37 |
+| S0380.221 | default missing `post_town` (unused metadata) | 1 |
+| S0380.222 | roof_construction 6 (thatched) + 7 (dwelling above) → None (inert) | 5 |
+| S0380.223 | `_part_geometry` early-return key contract (RR KeyError) | 5 |
+| **S0380.224** | **loose-jacket cylinder storage loss (Table 2 Note 1)** — was None'd out → zero loss | **22** (mean err +2.29 → +0.45) |
+| S0380.225 | §10.7 no-water-heating default A-F → 12mm loose jacket | 2 |
+| S0380.226 | Elmhurst "Jacket" cylinder insulation → loose-jacket code 2 (Summary path) | (unblocked case 19) |
+
+Headline at HEAD: **882 / 1000 computed, 41.8% < 0.5** (re-run the eval to refresh).
+
+---
+
+## ★ Active worksheet: simulated case 19 — the electric-storage-heater debug
+
+The user generated `sap worksheets/golden fixture debugging/simulated case 19/`
+(`Summary_001431 (2).pdf` + `P960-0001-001431 - 2026-06-04T174437.228.pdf`), purpose-built to
+hit the #1 cluster. It exercises **electric storage heaters** (SAP code 402, control 2402
+auto-charge, 7-hr off-peak tariff) + a **loose-jacket 210 L cylinder** + **WHS 911** (gas
+boiler for water only) + **room-in-roof gables (Party + Exposed) + an alternative wall +
+exposed floor + electric secondary**.
+
+**S0380.226 unblocked extraction** (the "Jacket" label was raising). The worksheet has FOUR
+blocks: **block 1 = rating** (UK-avg region 0; cost (255)=1816.58, SAP (258)=51, TF (53)=0.60,
+(51)=0.0330), **block 2 = demand** (postcode; CO2 (272)=3125.85, PE (286)=30271.76), blocks 3/4
+= the potential/improved variants. Pin the rating block for SAP/cost, the demand block for
+PE/CO2. Worksheet header line 116 lodges **"Separate Time Control: No"** (NOT in the Summary §15
+PDF — only in the P960 header).
+
+**Three slices shipped (S0380.227–229)** — closed the +9 cluster signature; SAP cont
+60.2 → **50.33** (worksheet ~51.22):
+
+| slice | line ref | fix | SAP cont |
+|---|---|---|---|
+| **S0380.227** | TF (53) 0.54→**0.60**; (59) h=3→**h=5** | dedicated DHW-only system (WHS 911) is NOT separately timed → no Table 2b ×0.9 (RdSAP 10 §10.5.1). `_separately_timed_dhw` gated on WHC ∈ {901,902,914}. Worksheet-pins S0380.224's loose-jacket (51)=0.0330/(53)=0.60/(55)=3.4531/(56-57)Jan=107.0456 at 1e-4. | 60.2→60.1 |
+| **S0380.228** | cost (255) | electric SECONDARY on off-peak bills at Table 12a `OTHER_DIRECT_ACTING_ELECTRIC` (7-hr high-frac **1.00** = £0.1529), not the flat off-peak low (£0.0550). Worksheet (242): "1.00*15.29 + 0.00*5.50". THE primary cost driver (−340). | 60.1→**50.67** |
+| **S0380.229** | (62) 2493.30→**3169.98** | dedicated water-heating boiler/circulator (WHC 911-931) feeds the cylinder via a primary loop → Table 3 row 1 primary loss applies (keyed off `water_heating_code`, since `_water_heating_main` returns the electric SPACE main). Restored the missing (59)=676.68 kWh/yr. | 50.67→50.33 |
+
+**The ONE remaining case-19 cause — the PV diverter (63b) — is S0380.232.** Worksheet
+header line 124 "Diverter = Yes"; Summary §19 "Diverter present: Yes". Per **SAP 10.2 Appendix
+G4 (PDF p.72-73)** surplus PV is diverted to the cylinder immersion:
+`S_PV,diverter,m = EPV,m × (1 − βm) × 0.8 × 0.9`, clamped to ≤ (62)m + (63a)m, entered as a
+NEGATIVE (63b)m. (64)m = (62)m + (63a)m + (63b)m + … → (219)m = (64)m / eff. All four G4
+inclusion conditions are met (PV connected to dwelling; cylinder 210 L > (43)=74.24; no solar
+HW; no battery). Worksheet (63b) annual ≈ −1097.67 kWh → (64) drops 3169.98 → 2072.31, (219)
+4876.9 → 3188.17. It ALSO changes the PV β-split (export drops: worksheet dwelling 1280.39 /
+exported 184.16 vs our 1496.20 / 1187.98 with no diverter). This is a 3-layer feature
+(extractor `Diverter present` → mapper flag → calculator (63b) + β-split interaction) —
+implement as one focused slice. Spec note p.5485: for the β calc, (219)m must EXCLUDE the
+diverter saving.
+
+Smaller residuals after the diverter lands: main fuel (211) ours 20250.22 vs ws 19910.30
+(+340), secondary (215) 3573.57 vs 3513.58 (+60), fabric (33) +1.0 (gable/alt-wall). Current
+demand block: CO2 (272) 3331.04 vs 3125.85, PE (286) 31653.23 vs 30271.76 — both will drop with
+the diverter (less grid import).
+
+**Debug recipe** (reuse the `/tmp/case19*.py` throwaways or rebuild):
+```python
+pages → ElmhurstSiteNotesExtractor(...).extract() → from_elmhurst_site_notes
+→ cert_to_inputs / cert_to_demand_inputs → calculate_sap_from_inputs
+# CI._cylinder_storage_loss_override(epc, main) → (57)m; CI._primary_loss_override(epc, age) → (59)m
+# CI._water_heating_worksheet_and_gains(epc=…, water_efficiency_pct=0.65, is_instantaneous=False,
+#   primary_age=<band>, pcdb_record=None) → wh_result with (45)/(46)/(57)/(59)/(62)/(64)
+```
+
+---
+
+## Remaining work, prioritised
+
+### A. Accuracy clusters (highest value)
+1. **PV diverter (S0380.232)** — closes case 19 to 1e-4 AND helps the real-PV cluster (45 certs,
+   mean 3.90). Fully spec'd in the case-19 section above (Appendix G4). **Has a worksheet** →
+   1e-4 bar. Do this first: it's the one open cause on a validated worksheet.
+2. **Electric storage heaters (cat 7, 40 certs, mean 5.25).** S0380.227-229 took it 7.33→5.25;
+   the case-19 PV diverter will help further. Beyond that the tail is per-cert — a **dedicated
+   cat-7 worksheet** (no PV, no diverter) would let you pin charge-control / responsiveness at
+   1e-4 instead of the ±0.5 lodged fallback.
+3. **Electric room heaters (cat 10, 48 certs, mean 5.26).** S0380.230-231 fixed the systematic
+   tariff bias (mean 9.49→5.26, signed +5.08→−0.86); the residual is now scattered per-cert
+   (e.g. `9836-5829` −29.5, an under-rater). A **cat-10 worksheet** pins the tail at 1e-4.
+4. **Non-PCDB gas boilers (cat 2, no idx, 91 certs, mean 3.18)** and **Flats (282, mean 2.57)** —
+   the next volume levers once the electric clusters are worksheet-pinned. Flats = geometry /
+   communal; start with the worst (`2100-5421` negative SAP).
+   - **`2100-5421-0922-1622-3463` diagnosed (S0380.234 session):** NOT a flat — `property_type 0`,
+     a **352 m² 2-storey uninsulated solid-wall** dwelling (wall_constr 3 / wall_ins 4 as-built;
+     roof_type 4, no roof insulation). Our space-heating demand is **71,084 kWh/yr** → (37)=995.93
+     W/K → SAP −24.8 (lodged 36), cost £14,045. This is the **`as-built insulated-assumed`**
+     U-value front ([[project_as_built_insulated_assumed_bug]]; S0380.209 fixed walls, "roof next"):
+     the uninsulated-roof / as-built U over-estimates demand on big old dwellings. API-only (no
+     worksheet → ±0.5 lodged fallback only); needs a generated worksheet or a roof-U spec audit to
+     pin. It is one outlier, not a cluster-wide flats bug.
+
+### B. Remaining raises (16 certs — all U-value / heat-loss-sensitive, NOT enum guesses)
+- **`gable_wall_type` 2 & 3 (14 certs).** RdSAP 10 **Table 4** RR walls: 0=Party (U=0.25),
+  1=Exposed (U=common wall), 2/3 = **Sheltered (U=external×R0.5)** + **Adjacent-to-heated
+  (U=0)**, code↔type order unconfirmed (schema says "not yet seen"). Needs (i) a worksheet to
+  pin which code is which + the U-values, and (ii) **calculator support** — the cascade only
+  has `gable_wall`/`gable_wall_external` kinds; Sheltered (R=0.5) and Adjacent (U=0) are new.
+  Best real example: `2818-3053-3203-2655-9204` lodges BOTH gable 2 and 3.
+- **`main_heating_category: 9` = warm air, mains gas (1 cert).** Needs §9 warm-air dispatch.
+- **`wall_insulation_thermal_conductivity` 3 (1 cert).** Verified it shifts wall U
+  (53.96→51.61 across λ) → worksheet-backed (the resolver's own discipline).
+- **`floor_heat_loss` 8 (2 certs).** Semantically unconfirmed; inert for the 2 observed
+  (non-Main bp) but potentially "heated space below" (→ should exclude the floor, a calculator
+  change). Don't guess.
+
+The clean mapper-enum raises are **exhausted** — every remaining raise changes the answer, which
+is what the strict-raise guard exists to prevent.
+
+---
+
+## ★ Additional worksheets that would help most (the user will generate these on request)
+
+The two electric clusters are now systematic-bias-free (S0380.227-231) but their TAILS sit at
+the ±0.5-vs-lodged fallback bar because **no worksheet validates them at 1e-4**. The three
+highest-value worksheets to ask the user for:
+1. **An electric ROOM-heater dwelling** (SAP code ~691, control 2601/2602/2603, Dual meter) —
+   pins the cat-10 tail (48 certs, mean 5.26) at 1e-4. Make it PV-free + cylinder-free to
+   isolate the space-heat path from the diverter/HW.
+2. **An electric STORAGE-heater dwelling distinct from case 19** (no PV, no WHS-911) — pins the
+   cat-7 tail (40 certs, mean 5.25): charge control (2401/2402), 7-hr vs 24-hr, responsiveness.
+3. **A room-in-roof with a SHELTERED gable and an ADJACENT-TO-HEATED gable** (Table 4 types
+   beyond Party/Exposed) — closes the `gable_wall_type` 2/3 raise (14 certs) and pins the
+   Sheltered (U=ext×R0.5) / Adjacent (U=0) U-values the calculator must add.
+
+Per worksheet send BOTH the **Summary PDF** (input) and the **P960/dr87 worksheet PDF** (the
+`(1)..(286)` ground truth). Drop them in `sap worksheets/golden fixture debugging/<name>/` and
+run the case-19 debug recipe.
+
+The original "design one property" guidance (kept below for reference) is what case 19 was
+built from.
+
+## What to generate — the single most productive worksheet (reference)
+
+Heating is one-per-property, so one worksheet can't cover all four broken heating types. But
+**fabric is independent of heating**, so the highest-ROI single artifact bundles the #1
+accuracy cluster with the fabric that closes the gable raises and pins the loose-jacket fix.
+
+**Build (in Elmhurst, a simulated case is fine — same as the existing `simulated case N`
+worksheets) ONE property:**
+
+> **A house heated by ELECTRIC STORAGE HEATERS, with a room-in-roof and a hot-water cylinder:**
+> - **Heating:** electric storage heaters (off-peak / Economy-7 tariff), with a clear control
+>   type. *This is the load-bearing choice — it validates the 39-cert cat-7 cluster.*
+> - **Hot water:** a cylinder with a **loose-jacket** insulation (not factory foam), a stated
+>   jacket thickness, and a cylinder thermostat. *Pins S0380.224's loose-jacket storage loss
+>   (56)m at 1e-4 — currently only direction-validated.*
+> - **Room-in-roof** with **two gable walls of different types** — ideally one **"Sheltered"**
+>   and one **"Adjacent to another heated space"** (plus, if the tool allows, a Party and an
+>   Exposed gable). *Gives the Table 4 U-values for gable_wall_type 2 & 3 and disambiguates the
+>   code order — closes the 14-cert raise.*
+> - **An extension (2nd building part)** with a different floor exposure (e.g. over unheated
+>   space or "to external air"). *Exercises multi-bp geometry + floor-exposure handling.*
+
+From that single worksheet I can pin, at 1e-4: the electric-storage space-heating lines
+((210)/(211)/space-heat), the loose-jacket storage loss (56)m, the RR gable U-values (30)/(32),
+and the multi-bp fabric (27)–(37). That's **one cluster + one fix-validation + the biggest
+raise + fabric**, all in one document.
+
+**If you'd rather do two:** add a second worksheet that is identical but with **electric room
+heaters** instead of storage heaters — together they cover cat 7 + cat 10 (≈ 82 certs, the
+two worst clusters). A third for a **community-heating flat** would cover cat 6 + the flat
+geometry cluster.
+
+### Then send me, per worksheet
+The **Summary PDF** (the Elmhurst input/site-notes) + the **worksheet PDF** (the `(1)..(286)`
+ground truth). With those I run both front-ends through the cascade and pin each line ref at
+1e-4, exactly as for the `with api 3` pair (S0380.218).
+
+---
+
+## Conventions (unchanged)
+One cause = one slice = one commit; spec citation (page+line) in the message; AAA tests
+(`# Arrange / # Act / # Assert`); `abs(x - y) <= tol` (not `pytest.approx`); SAP 10.2 only; no
+tolerance widening / xfail / rel-tol. New code passes pyright strict with ZERO NEW errors
+(baseline-compare with `git stash`; mapper.py / cert_to_inputs.py / heat_transmission.py carry
+pre-existing errors — compare counts). Stage files by name (the tree has unrelated
+`pytest.ini`/`scripts/` changes that must NOT be staged).
+`Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>`.

domain/sap10_calculator/docs/HANDOVER_FRESH_API_DEBUG.md

@@ -0,0 +1,160 @@
+# Handover — fresh-API cross-comparison + flagged-cert debugging
+
+Point-in-time note. Start from [`AGENT_GUIDE.md`](AGENT_GUIDE.md) for methodology, the
+1e-4 bar, the per-line debugging loop, the section helpers, and the suite command.
+
+- **Branch:** `feature/per-cert-mapper-validation`
+- **HEAD:** `6d9ef114` (S0380.218). Confirm with `git rev-parse HEAD`.
+- **Baseline (AGENT_GUIDE §4 suite):** `tests/domain/sap10_calculator/ backend/documents_parser/tests/`
+  → green (2392 passed, 1 skipped at HEAD; the golden + worksheet pins all pass).
+- **Next slice number:** **S0380.219**.
+
+> **S0380.218 (DONE) — Part 1 closed for the "with api 3" pair.** The two
+> certs the user dropped under `sap worksheets/with api 3/` —
+> `0340-2467-9260-2006-6521` (Summary_000922 / dr87 000922) and
+> `5500-5070-0822-0201-3663` (Summary_000920 / dr87 000920) — are **clean**.
+> Fetched fresh, run through BOTH front-ends, both paths agree to <1e-4 on
+> SAP/cost/CO2/PE AND reproduce the worksheet (255)/(272)/(286)/(33)/(37)
+> exactly. SAP integer = lodged (resid +0) on both. **No mapper/calculator
+> bug surfaced.** Dropped-field audit clean (only `created_at` +
+> `_normalize_shower_outlets`-handled shower keys). Locked in as golden
+> fixtures: 2 JSONs under `fixtures/golden/` + entries in `_EXPECTATIONS`
+> and `_WORKSHEET_PE_CO2` (test_golden_fixtures.py). The Summary path was
+> validated manually but is NOT pinned in a committed test (would need the
+> Summary PDFs copied into `backend/documents_parser/tests/fixtures/` + a
+> textract-preprocessed chain test) — a cheap follow-up if cross-mapper
+> parity wants a standing regression guard beyond the API-path golden pin.
+- **Pre-existing failures (NOT yours, out of scope):**
+  - `domain/sap10_ml/tests/test_rdsap_uvalues.py` — 2 stone-§5.6 thin-wall failures
+    (granite + sandstone band A, 3.7408 vs Table-6 1.7 cap). Run this suite when you touch
+    `rdsap_uvalues.py`.
+  - `datatypes/epc/domain/tests/test_from_rdsap_schema.py::TestFromRdSapSchema21_0_1::test_total_floor_area`
+    (145.82 vs 45.82) — fails at original HEAD `ec64c39d` too. This file is NOT in the §4
+    suite command.
+
+---
+
+## ★ THE TASK — fetch fresh from the EPC API and debug, with worksheet cross-comparison
+
+The previous session drove the **golden-fixtures cascade** (`cert_to_inputs` →
+`calculate_sap_from_inputs`) and concluded that the three then-flagged certs (7536, 2130,
+0240) are "0240-like" — API-only residuals not reproducible from the register JSON. The
+user pushed back ("going around in circles"), and the right next move is **fresh raw-API
+data + worksheet triples**, not more simulated worksheets.
+
+### Part 1 — two NEW certs with API + Summary + worksheet (cross-comparison)
+
+The user has **two certs that have all three artifacts**: the GOV.UK API JSON, the Elmhurst
+**Summary** PDF (site notes / input), and the Elmhurst **worksheet** PDF (the `(1)..(286)`
+ground truth). These are gold — they let you run BOTH front-ends (`from_api_response` and
+`from_elmhurst_site_notes`) through the same cascade and pin **both** against the worksheet
+at 1e-4. The user will provide the cert numbers + drop the PDFs. For each:
+
+1. Fetch the API JSON (see **Fetching** below).
+2. Run API path → cascade; run Summary path → cascade; pin **both** vs the worksheet line
+   refs (`pdftotext -layout` the worksheet; compare `(27)/(28a)/(29a)/(30)/(33)/(36)/(45)m/
+   (62)/(233a)/(233b)/(258)…`). Cross-mapper parity: the two paths must agree to 1e-4 AND
+   match the worksheet (memory `feedback_cross_mapper_parity_via_cascade`).
+3. The **first diverging line ref localises the bug** (AGENT_GUIDE §3): value present in
+   worksheet but cascade 0/wrong → calculator; input field absent in `epc` → mapper or
+   extractor. Fix one cause = one slice.
+
+### Part 2 — (secondary) re-check the previously-flagged certs on THIS branch
+
+A dashboard once flagged six certs (0240, 0390-2954-3640, 2130, 6035, 7536, 9390). **Those
+numbers are STALE — they came from a branch WITHOUT this branch's fixes** (the user confirmed
+this). Do not chase them. On THIS branch the picture is different and mostly settled:
+
+- 7536 (68.924, +1), 2130 (83.78, +2), 0240 (−1) — concluded **0240-like** (API-only
+  residuals; see per-cert notes below). 0390-2954-3640 pins at **+0** (exact).
+- 6035 (+2.19) and 9390 (community, −2) carry documented open residuals (see notes) but are
+  lower-priority and not worksheet-backed.
+
+So Part 2 is only worth touching if a **fresh fetch differs from the committed fixture**
+(curated/hand-corrected fixtures can mask raw-API mapper behaviour) — `diff` fresh vs fixture
+and debug the delta. Otherwise these are done; the real new work is **Part 1**.
+
+---
+
+## Fetching from the EPC API
+
+Token lives in `backend/.env` as `OPEN_EPC_API_TOKEN` (also `EPC_AUTH_TOKEN`). The exact
+mechanism (from `scripts/fetch_cohort2_api_jsons.py`):
+
+```python
+import httpx, os
+from dotenv import load_dotenv
+from infrastructure.epc_client.epc_client_service import EpcClientService
+load_dotenv("backend/.env")
+token = os.environ["OPEN_EPC_API_TOKEN"]
+resp = httpx.get(
+    f"{EpcClientService.BASE_URL}/api/certificate",
+    params={"certificate_number": "<CERT>"},
+    headers={"Authorization": f"Bearer {token}", "Accept": "application/json"},
+    timeout=EpcClientService.REQUEST_TIMEOUT,
+)
+payload = resp.json()["data"]   # <- this is the schema-21 JSON the mapper consumes
+```
+
+`EpcPropertyDataMapper.from_api_response(payload)` only supports `schema_type`
+`RdSAP-Schema-21.0.0` / `21.0.1`; it raises for others. The persisted golden fixture IS this
+`data` payload. So `diff <(fresh)` vs the committed fixture is apples-to-apples.
+
+---
+
+## Per-cert notes carried from the previous session (verify against FRESH data)
+
+- **7536 (+1)** — roof bug fixed (S0380.214: as-built sloping ceiling → Table 18 col 3).
+  Every per-element U matches Elmhurst (cases 15-17 worksheets). Concluded 0240-like; cont
+  68.924.
+- **2130 (+2)** — dropped measured wall insulation captured (S0380.215 → Table 8 U=0.32),
+  which **exposed** the true residual (the +1 was two offsetting bugs). PV β-split **proven
+  exact** vs simulated case 18 worksheet (onsite 970.77 / export 1713.40 to the decimal).
+  Gas PE factor exact (1.13). Concluded 0240-like; cont 83.78.
+- **0240 (−1)** — export-dropped 2013+ circulation-pump age (115 vs 41 kWh); WWHRS confirmed
+  inert (`shower_wwhrs=1` is the universal default across all 47 certs). User previously
+  decided NOT to re-pin. Concluded 0240-like.
+- **0390-2954-3640** — pinned +0 (oil combi, Table 3a row 1). The user's −6.85 flag is the
+  reconciliation mystery above — START HERE; it's the clearest signal of a fresh-vs-fixture
+  or different-engine gap.
+- **6035** — see memory `project_golden_coverage_state`: a user-simulated 6035 worksheet
+  closed to 1e-4, but "6035 remaining +19 PE needs its own worksheet"; flagged +2.19 SAP.
+- **9390** — community heat-network (S0380.212/.213 fixed the fuel-code collision + standing
+  charge); left at SAP −2 with a documented ~7% demand over-count (heat-source-eff default?).
+  Unpinned/retired. The user's −4.24 may be the same demand over-count on fresh data.
+
+---
+
+## What this session shipped (commits `ec64c39d..f895dd3a`)
+
+| slice | what |
+|---|---|
+| **S0380.214** | As-built "Pitched, sloping ceiling" (code 8) roof → RdSAP 10 Table 18 col (3) (band F 0.40→0.68, L 0.16→0.18) per §5.11 item 5-5 + note (b). Code-5 vaulted stays col (1) (cohort). Worksheet-validated (sim case 15). Re-pinned 7536. |
+| **S0380.215** | Captured dropped `wall_insulation_thickness_measured` (schema 21 didn't declare it → `from_dict` dropped it). 2130 Ext1 "measured"/100 mm → RdSAP Table 8 U=0.32 (was 0.55 default). Exposed 2130's true +2 residual. |
+| **S0380.216** | Extractor: handle pdftotext wrapping the §11 glazing-GAP column onto the glazing-TYPE token ("…16 mm or [1st]"). Fallback strip AFTER the direct lookup (preserves explicit interleaved keys). Unblocked running the cascade on hand-entered worksheet Summaries. |
+| **S0380.217** | Captured dropped `wall_insulation_thermal_conductivity` (schema → domain → mapper) and wired it into `u_wall`'s §5.8 λ resolver. Code 1 = default 0.04; unmapped codes raise. Zero cascade effect today (2130's §5.8 path doesn't fire). |
+| 3× docs | finalised 7536 / 2130 as 0240-like; corrected diagnoses. |
+
+**Audit method that found the dropped fields** (reuse it on the fresh certs): recursively
+compare raw JSON keys against the parsed schema dataclass fields — anything in the JSON but
+not a declared field is silently dropped by `from_dict`. The two real drops (2130's measured
+wall insulation + thermal conductivity) came from this. Re-run it on the fresh fetches; new
+certs may surface new dropped fields.
+
+---
+
+## Conventions (unchanged)
+
+One cause = one slice = one commit; spec citation (page + line) in the message; AAA tests
+(`# Arrange / # Act / # Assert`); assert with `abs(x - y) <= tol` (not `pytest.approx`);
+SAP 10.2 only; no tolerance widening / xfail / rel-tol. New code passes pyright strict with
+ZERO NEW errors — baseline-compare with `git stash` + `PYRIGHT_PYTHON_FORCE_VERSION=latest`
+(mapper.py / cert_to_inputs.py / heat_transmission.py / rdsap_uvalues.py carry pre-existing
+errors; compare counts). Stage files by name — the working tree has pre-existing unrelated
+changes to `pytest.ini` / `scripts/` that must NOT be staged.
+`Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>`.
+
+When you re-pin a golden cert, update `expected_sap_resid` (±0), `expected_pe_resid_kwh_per_m2`
+(±0.01) and `expected_co2_resid_tonnes_per_yr` (±0.001) to the exact post-fix values and
+append a slice note to the cert's `notes:` explaining the cause + spec/worksheet citation.
+Run the full §4 suite as the blast-radius check after any fabric/factor change.

domain/sap10_calculator/docs/HANDOVER_GLAZING_WINDOW_EXTRACTION.md

@@ -0,0 +1,94 @@
+# Handover — double_glazing fixture: glazing done, window-extraction open
+
+Point-in-time note for the agent owning the Elmhurst window extractor /
+mapper. Start from [`AGENT_GUIDE.md`](AGENT_GUIDE.md) for the 1e-4
+worksheet-pin methodology and the cascade pipeline.
+
+- **Branch:** `feature/per-cert-mapper-validation`. HEAD `8133521c`.
+- **Fixture:** the double_glazing "before" recommendation pair —
+  `sap worksheets/Recommendations Elmhurst Files/double_glazing/before/`
+  (`Summary_001431 (1).pdf` + `P960-0001-001431 - 2026-06-02T115533.961.pdf`).
+  The Summary is also committed as a test fixture:
+  `backend/documents_parser/tests/fixtures/Summary_001431_double_glazing.pdf`.
+- **Worksheet block to pin** (rating = block 1, region 0; demand = block 2,
+  postcode): SAP cont **57.2415**, cost (255) **1423.0955**, fabric (33)
+  **158.4548** / (37) **197.8463**; demand CO2 (272) **3486.0799**, PE (286)
+  **16796.5617**. (Blocks 3+ add PV/diverter — ignore for the "before" pin.)
+
+## Done this session (S0380.235-237) — DON'T redo
+
+| slice | what |
+|---|---|
+| **S0380.235** `3e45b7fa` | 5 missing Elmhurst §11 glazing labels → SAP10 Table 6b (`Secondary glazing`→7, `…- Normal emissivity`→11, `Triple pre 2002`→10, `Triple with unknown install date`→6, `Single glazing, known data`→15). |
+| **S0380.236** `ea35bed2` | Extension party-wall type read independently of "As Main Wall" (`_extract_extensions`): Main `CU`→0.5, Ext `U Unable to determine`→0.25. Worksheet **(32) party heat loss now exact** (32.573 vs 32.5725). |
+| **S0380.237** `8133521c` | `Secondary glazing - Low emissivity`→12. Double {1,2,3,7,13} + secondary {4,11,12} families now fully mapped. |
+
+**Confirmed already correct — do not touch:**
+- The calculator's window **U-adjustment `1/(1/U + 0.04)`** (SAP §3.2 curtain
+  correction) is exact: lodged 4.80→4.0268, 3.10→2.7580, 1.40→1.3258, all
+  match the worksheet to 1e-4. Our 14 extracted windows sum to **exactly
+  56.090**. The 1e-4 gap is NOT in the calculator.
+- Glazing label→code mapping (g_L is the only cascade effect; lodged U/g
+  drive §3/§6 via `_g_perpendicular` preferring the lodged value).
+
+## Open — current residual **SAP +1.13** (ours 58.37 vs ws 57.24), all in WINDOWS
+
+The Summary §11 lodges **17 physical window rows**; we end up with **14**
+`sap_windows`. Three windows are lost, in two distinct ways:
+
+### Cause 1 (HARD — read before touching `_is_elmhurst_roof_window`)
+The mapper routes the two `Double pre 2002` windows (lodged U 3.1 / 3.4) to
+**roof** windows via the `U > 3.0` backstop in
+`_is_elmhurst_roof_window` (`datatypes/epc/domain/mapper.py`, the final
+`return w.u_value > _ELMHURST_ROOF_WINDOW_U_THRESHOLD`). This fixture's
+worksheet bills them as **wall** windows (27).
+
+**The trap:** cohort cert **000516** has a window that is *byte-identical*
+in every extractable Summary field — `Double pre 2002`, U=3.1,
+`location="External wall"`, bp `Main`, orient `North-East` — and *its*
+worksheet bills it as a **roof** window (27a). Verified: gating the U>3
+rule on `location == "External wall"` makes this fixture pass but
+**breaks both 000516 pins** (`test_summary_000516_full_chain_…` and
+`test_from_elmhurst_site_notes_matches_hand_built_000516`).
+
+So identical Summary inputs are classified oppositely by the two
+worksheets. **No rule keyed on the fields we currently extract can satisfy
+both.** Resolving this needs a NEW disambiguating signal — likely a
+roof/wall or rooflight field Elmhurst lodges in §11 (or the BP roof
+structure) that the extractor doesn't yet capture. Do NOT flip the U>3
+heuristic to fix this fixture; it silently regresses 000516.
+
+### Cause 2 (tractable — a plain parsing miss)
+The extractor produces **16 windows from 17 §11 rows** — it drops the
+`Double glazing, known data` row (BFRC, lodged U=1.00 → adjusted 0.9615,
+1st Extension, area 1.00; worksheet "Windows 12" on Ext1). The label maps
+fine (→3); the physical row just isn't extracted. Fixing this alone won't
+pin the fixture (Cause 1 still blocks) but it's a real, isolatable
+extractor bug.
+
+## Tracer recipe (rebuild — the throwaway lived in /tmp)
+```python
+# from repo root, PYTHONPATH=/workspaces/model
+import re, subprocess; from pathlib import Path
+from backend.documents_parser.elmhurst_extractor import ElmhurstSiteNotesExtractor
+from datatypes.epc.domain.mapper import EpcPropertyDataMapper
+from domain.sap10_calculator.rdsap.cert_to_inputs import (
+    SAP_10_2_SPEC_PRICES, cert_to_inputs, cert_to_demand_inputs,
+    heat_transmission_section_from_cert)
+from domain.sap10_calculator.calculator import calculate_sap_from_inputs
+def pages(pdf):
+    n=int(re.search(r"Pages:\s+(\d+)",subprocess.run(["pdfinfo",str(pdf)],
+        capture_output=True,text=True).stdout).group(1)); out=[]
+    for i in range(1,n+1):
+        L=subprocess.run(["pdftotext","-layout","-f",str(i),"-l",str(i),str(pdf),"-"],
+            capture_output=True,text=True).stdout
+        out.append("\n".join(tok for ln in L.splitlines()
+            for tok in re.split(r"\s{2,}",ln.strip()) if tok))
+    return out
+D=Path("sap worksheets/Recommendations Elmhurst Files/double_glazing/before")
+sn=ElmhurstSiteNotesExtractor(pages(D/"Summary_001431 (1).pdf")).extract()
+epc=EpcPropertyDataMapper.from_elmhurst_site_notes(sn)
+# len(sn.windows)==16 (should be 17); len(epc.sap_windows)==14 (2 → roof, 1 dropped)
+```
+Per-window A×U on the worksheet uses the ADJUSTED U `1/(1/U_lodged+0.04)`;
+sum the §3 `(27)` lines to 60.5577 (we get 56.090 from 14 windows).

domain/sap10_calculator/docs/HANDOVER_MAPPER_BUGS.md

@@ -0,0 +1,264 @@
+# Handover — golden-cert mapper/cascade bugs (post-0240 wall fix)
+
+Point-in-time note. Start from [`AGENT_GUIDE.md`](AGENT_GUIDE.md) for methodology,
+the 1e-4 bar, the per-line debugging loop, and the suite command. This records the
+state after closing the 0240 investigation and fixing the first of several
+API-mapper/cascade bugs the audit surfaced.
+
+- **Branch:** `feature/per-cert-mapper-validation`
+- **HEAD:** `b9bbcecb` (docs after S0380.213). Confirm with `git rev-parse HEAD`.
+- **Baseline:** `2386 passed, 1 skipped, 0 failed` (AGENT_GUIDE §4 suite command).
+  ALSO run `domain/sap10_ml/tests/` when touching `rdsap_uvalues.py` — 2 PRE-EXISTING
+  stone-formula failures there, see Thread 1.
+- **Next slice number:** **S0380.214**.
+
+---
+
+## ★ CURRENT PRIORITY — drive golden-fixture SAP residuals to ZERO
+
+`_EXPECTATIONS` in `test_golden_fixtures.py` holds **53 pinned golden certs**. The suite
+is GREEN. **Only 3 have a non-zero SAP integer residual**, and they split into two kinds:
+
+| cert | lodged | cont SAP | resid | nature (from the cert's `notes:`) |
+|---|---|---|---|---|
+| **7536-3827-0600** | 68 | **69.071** | **+1** | +0.57 over — multi-age bps (Main D / Ext1 L / Ext2 F); **glazing U** (S0380.97 set glazing_type=2 → Table 24 spec U=2.0, but the cert's lodged U "appears higher than the spec default") |
+| **2130-1033-4050** | 82 | **83.349** | **+1** | +0.85 over — end-terrace + 1 ext, gas combi PCDB 17505, **2× PV arrays**; SAP +1 came from the **cohort PV-β cascade interaction** (S0380.45/.49), not a pinpointed fabric line; PE residual −8.22 sits in gas-combi PE + secondary credit |
+
+**These are TWO DIFFERENT root causes — not a shared one** (an earlier audit label calling
+both "multi-part wall" was wrong; trust the `notes:` above).
+
+- **7536** is the more tractable: a clear **glazing-U** hypothesis. S0380.97 forced
+  `glazing_type=2` to the Table 24 default U=2.0; the note suspects the cert's true per-bp
+  glazing U is higher (multi-age D/L/F geometry). Walk §3 window `(27)` per-bp vs the lodged
+  register window rating; the lever is likely the glazing U for one of the extensions. ASK
+  the user for a simulated Elmhurst worksheet mirroring 7536's glazing (double-glazed,
+  multi-age bps) to pin the true `(27)` U rather than guess.
+- **2130** is harder: the SAP +1 is a PV-β / cohort *cascade interaction*, not a single
+  fabric line. Its PE residual (−8.22) is a documented gas-combi-PE + secondary-credit
+  deferral. Decompose which metric drives the integer flip (cost/EI vs PE) before touching
+  anything; this one may need the PV/secondary path, not fabric.
+
+Both certs are API-only (no worksheet) → bar is ±0.5 SAP vs lodged; the goal is the integer
+flip (69→68 / 83→82), i.e. shave ~0.57 / ~0.85 off the continuous SAP. Per the session
+methodology lesson, ASK for a worksheet rather than guess a U-value or factor.
+
+**0240 (−1) is NOT driveable from the JSON and the user has decided NOT to re-pin it —
+document the cause only.** Continuous SAP is 72.462; the true SAP is **72**. The lodged
+**73 requires a "2013 or later" circulation pump (41 kWh)**; 0240's open-data API lodges
+`central_heating_pump_age=0` = **Unknown → 115 kWh**. The encoding was proven across 13
+API+Summary pairs (`0`=Unknown, `2`=2013+). The export did not preserve the pump age that
+produced the lodged 73, so 73 is unreachable without inventing data. Both fabric bugs that
+masked it are now fixed (wall S0380.209 + roof S0380.211 → cont 72.462). **Leave the pin at
+`actual_sap=73, expected_sap_resid=-1`; the notes already record this.** Driving it to zero
+would mean fudging the pump age — don't.
+
+Latent (lower priority): **9390** (community, −2, **unpinned**/retired) ~7% demand
+over-count — see Thread 2.
+
+---
+
+## What this session shipped
+
+| slice | what |
+|---|---|
+| **S0380.208** | Promoted **simulated case 7** (combi swap of case 6) to an e2e fixture. PROVED the condensing-oil-combi (SAP code 130, no cylinder, combi instantaneous DHW, Eq D1, Table 3a keep-hot) path is **exact at 1e-4** with zero calculator changes → exonerated the heating as the source of 0240's residual. |
+| **S0380.209** | Fixed the **API-path wall U** "as built, insulated (assumed)" bug — routes to the as-built age-band row, not the 50 mm retrofit bucket. New `_described_as_retrofit_insulated` in `heat_transmission.py`. Worksheet-validated by case 9 (sandstone J → 0.35) + case 10 (solid brick J → 0.35). Re-pinned 0240 PE +1.8687 → +5.5044, CO2 +0.0907 → +0.2757 (SAP integer 72 unchanged). |
+| **S0380.210** | **CLOSED cert 0390** (Thread 3). Cavity wall "as built, **partial** insulation (assumed)" (type 4) was mis-routed to the Table 6 "Filled cavity" row (band F 0.40) → should be "Cavity as built" (band F 1.0). New `_cavity_described_as_filled` in `rdsap_uvalues.py` excludes "partial insulation" from the filled trigger (keeps "insulated (assumed)" → filled). SAP +7 → +0, PE −27.97 → +0.53, CO2 −2.71 → −0.12. Mirrors S0380.209 on the cavity path. |
+| **S0380.211** | **CLOSED Thread 1 (roof).** 0240 Ext1 vaulted (code 5) NI roof returned 0.68 (§5.11.4 50 mm) → should be Table 18 col (1) age-band (band J 0.16), matching 33 cohort-2 `ND` vaulted roofs. New `u_roof(is_sloping_ceiling=...)` flag threaded from heat_transmission (codes 5/8). 0240 PE +5.50 → +1.52, CO2 +0.28 → +0.07 (SAP 72). Also corrected the S0380.210 cavity unit test in `domain/sap10_ml/tests/` (suite-command gap — see Thread 1). |
+| **S0380.212** | **Thread 2 CO2/PE collision FIXED.** EPC fuel 20 = "mains gas (community)" collided with Table-12 biomass code 20 → community CO2 6.4× low. New `_heat_network_factor_fuel_code` translates 20→51 for heat-network mains only (5 sites: SH+HW CO2/PE/price). 9390 CO2 0.44→3.03 t (lodged 2.8), PE 204→220. Case-14-validated ((367) 0.2100 / (467) 1.1300). Cost +4 tail open. |
+| **S0380.213** | **Thread 2 cost +4 FIXED** via the heat-network standing charge. API community fuel 20 isn't a Table-32 gas code → `_is_gas_code` False → £0 standing (vs SAP 10.2 Table 12 note (l) £120; case 14 `(351)`=£120). New `_heat_network_standing_charge_gbp` (£120 full / £60 DHW-only, §C3.2) REPLACES the fuel standing for heat-network mains (no double-count; CH corpus stays £120). 9390 SAP +4 → -2 (exposes a ~7% demand over-count — follow-up). |
+
+Both also carry a memory: [[project_case7_combi_exonerated]], [[project_as_built_insulated_assumed_bug]].
+
+---
+
+## The 0240 verdict — RESOLVED, not closable to 73
+
+**0240's true SAP is 72**, proven three independent ways:
+- Elmhurst **case 8** (pump=Unknown, 0240's actual lodged value) → worksheet SAP **72**.
+- Elmhurst **case 9** (correct sandstone wall 0.35 + sloping roof 0.25) → SAP **72**.
+- Our cascade with **both** the wall (done) and roof (pending) bugs fixed → SAP cont **72.31**.
+
+The register's **73 requires a "2013 or later" circulation pump (41 kWh)** — Elmhurst
+**case 7** with that pump = 73. But 0240's API lodges `central_heating_pump_age=0`
+= **Unknown** → 115 kWh. The encoding was **proven from 13 API+Summary pairs**:
+`0`="Unknown" (9 pairs), `2`="2013 or later" (4 pairs). The open-data export did not
+preserve the pump age that produced the lodged 73. **It is genuinely unreachable from
+the JSON.** Do not chase 0240 to 73; re-pin to its correct 72 once the roof lands.
+
+`pump_age` enum (verified): `0`=Unknown→115, `1`=Pre-2013→165, `2`=2013+→41
+(`_TABLE_4F_CIRCULATION_PUMP_KWH_BY_AGE` in `cert_to_inputs.py`).
+
+---
+
+## THE METHODOLOGY LESSON FROM THIS SESSION (read this)
+
+The 0240 baseline (cont 72.39) was **two offsetting bugs**: a wall U **under**-count
+(0.25 vs 0.35, less loss) masking an Ext1 roof U **over**-count (0.68 vs ~0.25, more
+loss). Fixing one alone moves the residual the "wrong" way — fix both
+([[feedback_software_no_special_handling]]). And: **Elmhurst is the arbiter, not the
+spec text** — twice this session a confident spec/first-principles read was wrong and
+a generated worksheet settled it (`NI`=not-indicated not "none"; pump `0`=Unknown).
+**Generate a worksheet rather than guess a U-value or factor.** The user generates
+Elmhurst worksheets readily (cases 7–10 done) — ask for one.
+
+---
+
+## THREAD 1 — Roof fix — **CLOSED (S0380.211)**
+
+0240's Ext1 (BP2) lodges `roof_construction=5` (vaulted), `NI` thickness, "Pitched,
+insulated (assumed)", band J → the cascade hit `u_roof`'s
+`insulation_thickness_mm==0 and _described_as_insulated` override → **0.68** (the
+§5.11.4 retrofit-50 mm joist row). A vaulted/sloping ceiling has no joist void, so per
+RdSAP 10 §5.11 Table 18 (p.45) it takes the **column (1) age-band default (band J =
+0.16)**, NOT 0.68.
+
+**The arbiter was the cohort, not case 11 — a methodology trap avoided.** The handover
+above guessed the value was col-3 **0.25** (→ cont 72.31), citing case 9. That was
+WRONG. The decisive evidence: **33 cohort-2 certs lodge `ND` (thickness None) vaulted
+roofs** (`roof_construction=5`, band D) that already pin to their dr87 worksheets at
+**0.40 = Table 18 col (1)**. 0240's only difference is the `NI` sentinel (insulation
+present, unknown thickness), which uniquely hit the 0.68 override. So the spec-correct
+value is **col (1) 0.16**, and 0240 lands at **cont 72.4617**, integer 72 — NOT 72.31.
+A first broad attempt (route sloping → col-3 `_FLAT_ROOF_BY_AGE`) broke all 33 cohort
+certs (band D col-3 = 2.30 vs worksheet 0.40) — that failure is what revealed the
+col-1 answer. Lesson: when a U-value change moves worksheet-pinned cohort certs off
+their pins, the change is wrong; the cohort worksheets are ground truth.
+
+**Implementation:** new `u_roof(is_sloping_ceiling=...)` flag, threaded from
+`heat_transmission` for `roof_construction_type` containing "sloping ceiling" (code 8)
+or "vaulted" (code 5). Fires only on the `NI` case (thickness 0 + "insulated
+(assumed)") → col (1); the `ND`/None path is untouched (already col 1) and a normal
+pitched-with-loft roof still takes the §5.11.4 50 mm row (flag defaults False). 0240
+PE +5.5044 → +1.5181, CO2 +0.2757 → +0.0728 (SAP 72 unchanged). Re-pinned in
+`test_golden_fixtures.py`.
+
+**⚠ Suite-command gap discovered:** the AGENT_GUIDE §4 suite command does NOT run
+`domain/sap10_ml/tests/`, where `u_roof`/`u_wall` unit tests live. S0380.210 shipped a
+broken `test_u_wall_cavity_..._filled_cavity_row` there unnoticed; S0380.211 corrected
+it (→ `..._as_built_row`). **When touching `rdsap_uvalues.py`, also run
+`domain/sap10_ml/tests/`.** Two PRE-EXISTING failures live there (stone §5.6 thin-wall
+formula 3.7408 vs Table-6 1.7 cap, granite + sandstone band A) — they fail at HEAD
+`58ff7d88` too, unrelated to this branch.
+
+---
+
+## THREAD 2 — Community fuel-code collision (cert 9390) — **CO2/PE FIXED (S0380.212); cost +4 open**
+
+Cert **9390-2722-3520** (community mains-gas boiler, `sap_main_heating_code=301`,
+`main_fuel_type=20`). Authoritative: `datatypes/epc/domain/epc_codes.csv`
+(RdSAP-Schema-17.0) `main_fuel,20,mains gas (community)`.
+
+**Root cause (the collision):** the EPC `main_fuel_type` enum and the SAP Table 12 /
+Table 32 numbering overlap in **18–25** — EPC 20='mains gas (community)' but Table-12
+code 20 is solid biomass (CO2 0.028). `co2_factor_kg_per_kwh`/`primary_energy_factor`/
+`unit_price_p_per_kwh` check the Table-12 dict FIRST, so the EPC community fuel got the
+biomass factor instead of translating 20→51 (community mains gas: CO2 0.210, PE 1.130).
+
+**S0380.212 fix:** new `_heat_network_factor_fuel_code(main)` translates the EPC community
+fuel → Table-12 code via `API_FUEL_TO_TABLE_12`, but ONLY for heat-network mains
+(`_is_heat_network_main`) so a genuine biomass boiler keeps its raw factor. Applied at
+**five** sites — space-heating CO2/PE/unit-price + water-heating (WHC 901) CO2/PE (9390's
+HW is ALSO community gas, so both paths needed it). Worksheet-validated by **case 14**
+(community boilers + mains gas, code 301): `(367)` CO2 0.2100, `(467)` PE 1.1300 = the
+Table-12 code-51 values. 9390 CO2 **0.44 → 3.03 t** (lodged 2.8 — spec-correct factor over
+the API-only register residual; 9390 is unpinned, retired P2.2 per ADR-0010 §10), PE
+**204 → 220** (the prior 204≈205 was the collision coinciding with the register residual).
+Summary path uses code 1 (no collision) → CH1-6 corpus untouched. Locked by 2 unit tests
+in `test_cert_to_inputs.py`.
+
+**Cost +4 — FIXED (S0380.213), via the standing charge (NOT cost scaling).** The earlier
+"missing 1/heat_source_eff cost scaling" hypothesis was WRONG: case 14's 10b block shows
+the heat price (`(340)`/`(307)` = 4.24 p/kWh) is applied to delivered heat, NOT scaled —
+and Table-32 code 51 already = 4.24 p/kWh (the price collision was harmless, 4.23≈4.24).
+The real gap was the **£120 heat-network standing charge** (SAP 10.2 Table 12 note (l) +
+§C3.2; case 14 `(351)` = £120): the API community fuel (20) isn't a Table-32 gas code so
+`_is_gas_code` returned False → £0 standing (the Summary path masks it via code 1). New
+`_heat_network_standing_charge_gbp` REPLACES the fuel standing for heat-network mains
+(£120 full / £60 DHW-only) — not additive, so the CH corpus (already £120 via the gas
+branch) isn't double-counted to £240. 9390 SAP +4 → **-2**.
+
+**STILL OPEN — 9390 ~7% demand over-count (SAP -2):** the standing fix EXPOSED it — PE 220
+vs lodged 205, CO2 3.03 vs 2.8 all run ~7% high. Likely the heat-source-efficiency default
+(`_HEAT_NETWORK_HEAT_SOURCE_EFFICIENCY[301]=0.80`) being too low for 9390's actual scheme,
+or a fabric/demand difference. 9390 is API-only (no worksheet) + unpinned, so this is a
+low-priority residual; needs a 9390-specific efficiency/fabric investigation.
+
+---
+
+## THREAD 3 — Cert 0390 +7 — **CLOSED (S0380.210)**
+
+**0390-2954-3640** (detached, TFA 360, age F). The boiler was correctly resolved
+(PCDB 9005 Firebird S, 86.4% winter); the gap was a single fabric mis-route. Walking
+the §3 cascade localised it to the Main **cavity wall**: lodged `wall_construction=4`,
+`wall_insulation_type=4` (as-built/assumed), description "Cavity wall, as built,
+**partial insulation** (assumed)". The cascade routed it to the Table 6 **"Filled
+cavity"** row (band F = 0.40) because `_described_as_insulated` matches the "partial
+insulation" substring. Per **RdSAP 10 Table 6 (England)** an as-built partial-fill
+cavity uses **"Cavity as built"** (band F = **1.0**), not filled — a genuine fill
+lodges the distinct "Cavity wall, filled cavity" (`wall_insulation_type=2`). This
+mirrors the worksheet-validated solid-brick rule from S0380.209 (cases 9/10).
+
+Fix: new `_cavity_described_as_filled` predicate, used **only** in u_wall's cavity
+filled-row branch, excludes "partial insulation" while keeping "insulated (assumed)"
+→ filled. Wall HLC +53.6 W/K lifted all four metrics together: **SAP +7 → +0**,
+PE −27.9745 → +0.5281, CO2 −2.7134 → −0.1189. Bands I-M coincide († footnote) so
+0535(M)/7536(L) are unaffected. Re-pinned in `test_golden_fixtures.py`.
+
+**Diagnosis lesson / latent follow-up:** the fix collided with an existing test,
+`test_cavity_as_built_insulated_assumed_uses_filled_cavity_row` (heat_transmission
+tests). That test (from early "slice S-B25") asserts a cavity **"insulated (assumed)"**
+→ filled row, citing only an *assumption* ("the assessor has determined the cavity is
+filled"), **never worksheet-validated** — and it is the OPPOSITE conclusion from the
+worksheet-backed solid-brick sibling. The narrow S0380.210 fix leaves it untouched
+(no current cert exercises it at a band where as-built ≠ filled). **Open question for a
+future worksheet:** does a cavity lodged "as built, insulated (assumed)" (type 4)
+belong on the filled row (0.7 at E) or the as-built row (1.5 at E)? If a worksheet
+says as-built, fold "insulated (assumed)" into the as-built routing too and retire
+that test.
+
+---
+
+## Full audit — all golden certs with non-zero SAP residual
+
+| cert | SAP resid | diagnosis |
+|---|---|---|
+| 0390-2954-3640 | ~~+7~~ **+0** | **CLOSED S0380.210** — cavity partial-insulation → as-built row |
+| 9390-2722-3520 | −2 (unpinned) | **CO2/PE collision FIXED S0380.212** + **standing charge S0380.213** (SAP +4→−2); remaining ~7% demand over-count (heat-source-eff default?) |
+| 0240-0200-5706 | −1 | NOT a bug — unpreserved 2013+ pump; true SAP 72. Roof PE-pin tightened by **S0380.211** (PE +5.50 → +1.52) |
+| 2130-1033-4050 | +1 | minor fabric precision (multi-part solid-brick wall); low value |
+| 7536-3827-0600 | +1 | minor fabric precision (multi-bp D/L/F cavity); low value |
+
+All others pin at residual 0.
+
+---
+
+## Worksheets
+
+- **Available** (user-generated, `sap worksheets/golden fixture debugging/simulated case N/`):
+  case 7 (combi), case 8 (unknown pump), case 9 (sandstone wall + sloping roof),
+  case 10 (solid-brick wall), **case 11** (001431 sloping-ceiling Unknown roof — used to
+  scope Thread 1; the cohort `ND` certs were the real arbiter), **case 12** (community
+  CHP **coal**, code 302), **case 13** (community CHP **mains gas**, code 302). Case 7's
+  Summary is the only one mirrored into tracked fixtures
+  (`backend/.../Summary_001431_case7.pdf`, used by the e2e pin).
+- **Still needed (Thread 2):** a **code-301** (community boilers, NOT CHP) + **mains gas**
+  worksheet to pin 9390's exact PE/CO2/cost. case 13 is code-302 CHP-gas: it confirms the
+  community-gas direction (heat-network `(386)` CO2 0.2456) but the CHP heat-power split
+  differs from 9390's boiler scheme. **API `main_fuel_type=20` = community/district
+  heating from mains gas → SAP Table 12 code 51** (CO2 0.210, PEF 1.130).
+
+## Pointers
+- Golden pins + slice history: `tests/domain/sap10_calculator/rdsap/test_golden_fixtures.py`.
+- Wall fix: `domain/sap10_calculator/worksheet/heat_transmission.py`
+  (`_described_as_retrofit_insulated`, the `wall_ins_present` gate) +
+  `tests/.../worksheet/test_heat_transmission.py`.
+- Roof code: `domain/sap10_ml/rdsap_uvalues.py` `u_roof` (L708 + Table 18 dicts L637-668).
+- Community/heat-network CO2/PE/cost: `cert_to_inputs.py` ~L2749-2880, L1837
+  (`_main_fuel_code`), `tables/table_12.py` + `table_32.py` (`co2_factor_kg_per_kwh`,
+  `API_FUEL_TO_TABLE_12/32`).
+- Process: one slice = one commit, spec citation (page+line), AAA tests, `abs(x-y)<=tol`
+  not `pytest.approx`, `Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>`.
+  SAP 10.2 only. No tolerance widening. mapper.py + cert_to_inputs.py each carry 32
+  pre-existing pyright errors; heat_transmission.py + rdsap_uvalues.py carry their own —
+  baseline-compare with `git stash` for net-zero NEW.

domain/sap10_calculator/docs/HANDOVER_POST_S0380_195.md

@@ -0,0 +1,147 @@
+# Handover — post S0380.195 (gas-combi site-notes + RR/floor bugs; 6035 OPEN)
+
+Point-in-time note. Start from [`AGENT_GUIDE.md`](AGENT_GUIDE.md) for methodology,
+accuracy bar, and pipeline — this records *what this session did* and *what is open*.
+
+- **Branch:** `feature/per-cert-mapper-validation`
+- **HEAD:** `4a21717d` (S0380.195)
+- **Baseline:** `2341 passed, 1 skipped, 0 failed`. Verify with the §4 suite command.
+
+---
+
+## What this session shipped (S0380.190–195 + 1 extractor fix)
+
+| Slice | What | Spec |
+|---|---|---|
+| **.190** | Gas-combi site-notes `main_fuel_type` derivation. Newer Elmhurst export lodges §14.0 Fuel Type EMPTY + SAP code 104 → `MissingMainFuelType` blocked ALL gas-combi Summary certs. Derive carrier from §15.0 Water Heating Fuel Type for Table 4b gas-boiler codes 101–119 (NOT "104→mains gas" — Table 4b gas codes span mains gas/LPG/biogas; §15.0 disambiguates). `_elmhurst_gas_boiler_main_fuel`. | SAP 10.2 Table 4b p.168 |
+| extractor fix | Windows-table header remnant ("value value Proofed Shutters") leaked into the FIRST window's `glazing_type` (layout `before_start=0` reaches the wrapped header). Trim prefix to the glazing-start word. | — |
+| **.191** | Promoted sim case 1 (single-part gas combi) to e2e harness `001431`, 11 pins @1e-4. Resolved the handover's "+0.0007 SAP" as a display-rounded-ECF target artifact. | — |
+| **.192** | **Simplified room-in-roof bug.** A Simplified RR (assessment "Simplified") lodges PLACEHOLDER slope/ceiling L×H (40 m ceiling height, 32 m slope). Spec derives one timber-framed remaining area `A_RR = 12.5√(A_floor/1.5) − Σgables`. The cascade already computes this (`has_roof_lodgement` gate in heat_transmission.py) but `_map_elmhurst_rir_surface` emitted the placeholder slope/ceiling → 1024+160 m² roof → **7.5× heat-loss explosion (SAP −14.6)**. Fix: drop roof-going surfaces for Simplified. API path (6035) already correct via scalar gable fields. | RdSAP 10 §3.9.1 p.21 |
+| **.193** | **Suspended-floor (12) sealed rule.** Rule (a) "floor U<0.5 → sealed 0.1" applies only when a U-value is SUPPLIED; an as-built/default U falls to (b)→unsealed 0.2. Cascade fed the computed default U into (a) → wrongly sealed → ~450 kWh space-heat understatement. Fix: gate (a) on `floor_u_value_known`. | RdSAP 10 §5 p.29 |
+| **.194** | Sim case 3 (8 windows, symmetric HLP) → e2e `001431_rr8`, 11 pins @1e-4. | — |
+| **.195** | Sim case 4 (6035 floor geometry: Main ground HLP 15.99 + first 8.32) → e2e `001431_6035`, 11 pins @1e-4. | — |
+
+Net: 4 new Elmhurst-only e2e fixtures (cases 1–4 of cert 001431), all @1e-4. The
+worksheet Summaries are mirrored into `backend/documents_parser/tests/fixtures/`
+(`Summary_001431_gas_combi.pdf`, `_rr_ext`, `_rr8w`, `_6035`); source Summary +
+P960 worksheet tracked under `sap worksheets/golden fixture debugging/simulated
+case {1..4}/`.
+
+**The .195 commit message and the `_elmhurst_worksheet_001431_6035.py` docstring
+claim 6035's +19 PE is "lodged divergence." THAT CLAIM IS RETRACTED — see below.**
+
+---
+
+## OPEN (the priority) — golden cert 6035 residual is REAL, not divergence
+
+`tests/.../test_golden_fixtures.py` pins cert `6035-7729-2309-0879-2296`:
+`actual_sap=70, expected_sap_resid=-2, expected_pe_resid=+19.16,
+expected_co2_resid=+0.42 t`. **All three exceed the ±0.5 SAP / small-CO2 fallback
+bar.** A −2 SAP is not rounding. 6035 was lodged **2025-11-11** under
+RdSAP-Schema-21.0.1 / SAP 10.2 (software `5.02r0328`) — the SAME methodology we
+target, so it is NOT a version artifact.
+
+### What we know
+- **The cascade reproduces Elmhurst's WORKSHEET engine** for this archetype: sim
+  cases 1–4 (Main+Ext+RR+suspended-floor+gas-combi-104) all pin @1e-4 on all 11
+  Block-1 line refs.
+- **Case 4 ≈ 6035.** Identical: 2 BPs, age A, solid-brick walls (Main ins, Ext
+  as-built), RR floor 29.75, floor areas, **Main floors HLP 15.99/8.32**, doors,
+  heating (104/control 2106), 8 windows by **area + BP + 7/8 orientations**.
+  Remaining input diffs case4-vs-6035:
+  1. the **3.82 m² window**: North in case 4, **South** in 6035 (only window diff);
+  2. **lighting bulbs**: case 4 cascade lighting 262 vs 6035's **364** (6035 lodges
+     9 low-energy + 2 incandescent; case 4's Summary lighting parsed as None);
+  3. **meter type** "Dual" (case4) vs API **2** (6035);
+  4. 6035 lodges `cylinder_size=1` (case 4 none) — appears immaterial (HW matches).
+- **Controlled test:** flipping case 4's 3.82 window N→S raises SAP only **+0.25**
+  (68.19→68.44). Nowhere near +2. So orientation does NOT explain the gap.
+- **The energy/demand model looks ~right per-end-use.** Cascade DEMAND
+  (postcode) costs ≈ 6035's lodged costs: heating £1278 vs lodged £1285, HW £225
+  vs £217, lighting £103 vs £103. So the −2 SAP lives in the **RATING block**
+  (UK-avg): cascade rating cost 948.59 → ECF 2.31 → SAP 67.81; register implies
+  cost ~£886 / ECF 2.15 / SAP 70. **Plus the CO2 (+0.42 t) is unexplained.**
+- Neither bug fixed this session touches 6035 (its RR uses the API scalar-field
+  path, already correct; its floor U=0.63 ≥ 0.5 was already "unsealed").
+
+### The contradiction to resolve
+Elmhurst-worksheet-for-case4-inputs = **68**, 6035-register = **70**, same
+methodology, inputs nearly identical, and the known diffs explain only ~+0.25.
+Either (a) 6035's register was produced from inputs materially different from the
+golden JSON in a rating-relevant way we can't see, or (b) there's a real cascade
+bug only 6035's exact combination triggers (the simulated cases didn't hit it).
+
+### ★ BREAKTHROUGH LEAD (end of session) — API-mapper roof/RR over-count
+The user's hypothesis ("something missing from the API mapper") is CONFIRMED.
+Diffing **6035 (API path) vs case 4 (site-notes path)** at the SECTION level
+(`heat_transmission_section_from_cert`) — with near-identical fabric — exposes a
+cross-mapper parity break that should not exist:
+
+| §3 line | case4 (site-notes) | 6035 (API) | Δ |
+|---|---|---|---|
+| **roof W/K** | **78.33** | **130.73** | **+52.39** |
+| party W/K | 36.86 | 0.00 | −36.86 |
+| (33) fabric heat loss | 290.72 | 304.66 | +13.94 |
+| (31) total ext area | 231.02 | 242.74 | +11.72 |
+| walls / floor / windows / doors | — | — | ≈0 |
+
+**The roof +52 W/K is the prime suspect for the whole 6035 residual** (52 W/K of
+spurious heat loss ≈ the −2 SAP / +19 PE / +0.42 t CO2). Root cause is the RR/roof
+representation feeding two DIFFERENT cascade paths:
+- **case 4 (site-notes):** `sap_room_in_roof.detailed_surfaces=[gable_wall_external,
+  gable_wall]`, scalar gable lengths = None, `roof_construction=None` → cascade's
+  Detailed-loop residual path (`12.5√(A_floor/1.5) − Σwalls`) → roof 78.33. ✓
+  (pins to case-4 worksheet @1e-4).
+- **6035 (API):** `detailed_surfaces=None`, scalar `gable_1/2_length_m=4.65`,
+  **`roof_construction=4`** → cascade's SCALAR RR path (heat_transmission.py
+  ~363-460 + ~853-875) AND a separate `roof_construction=4` main-roof element →
+  roof 130.73. Likely DOUBLE-COUNTS the main roof over the full footprint with the
+  RR, or the scalar A_RR path over-states the area.
+
+Hand-check: for 6035 the correct roof ≈ RR remaining (12.5√(29.75/1.5) − 2×11.39
+= 32.88 × 2.30 = 75.6) + main-loft residual (41.73−29.75=11.98 × 0.14 = 1.68) +
+ext roof (7.21 × 0.14 = 1.01) ≈ **78.3** (matches case 4). The API path's 130.73 is
+~52 too high.
+
+**START HERE:** instrument the API RR/roof path for 6035. Compare
+`_api_build_room_in_roof` (mapper.py ~2713) output + `roof_construction=4`
+handling vs the site-notes detailed_surfaces path. Find where the extra ~52 W/K
+roof comes from (main-roof-area double count with RR, or scalar A_RR over-state).
+Fix so the API path matches the site-notes path (cross-mapper parity), then re-pin
+6035's golden residual (should collapse toward 0). The party=0 (party_wall_
+construction=3) is secondary — verify 3=solid U=0 is correct first.
+
+This is a CALCULATOR/MAPPER bug, not lodged divergence — the byte-exact-worksheet
+plan below is now a fallback only.
+
+### Fallback — byte-exact 6035 worksheet ("simulated case 5")
+Ask the user to generate case 5 = case 4 with EVERY remaining input matched to
+6035: **3.82 m² window → South**, **lighting = 9 low-energy + 2 incandescent**,
+**meter type matched**, **cylinder matched**. Then:
+- If the worksheet SAP = **70** → real cascade bug. Diff cascade vs worksheet
+  line-by-line (start §6 solar gains (74)–(83) for the south window, §8 lighting
+  (232)/Appendix L, then §10a/§12 rating cost/ECF and §12/§13 CO2).
+- If the worksheet SAP = **68** → the register's 70 is the anomaly (lodged from
+  different inputs); 6035 becomes a documented register-vs-worksheet divergence.
+
+Parallel angle worth a look NOW (no new worksheet needed): the **lighting energy**
+(cascade 364 for 9 LE + 2 inc, TFA 128) — verify against SAP 10.2 Appendix L; and
+the **CO2 (+0.42 t)** decomposition by carrier (the demand-cost match suggests the
+energy is right, so a CO2-FACTOR or rating-block issue is implicated).
+
+---
+
+## Carry-over (lower priority, from the prior handover)
+- `transform.py:973` treats `wall_construction in (5,6)` as timber-frame for the
+  ventilation structural-ACH split, but 6 = system-built (masonry); only 5/7/8 are
+  timber/cob/park. Possible latent ventilation-ACH bug — verify before touching.
+- Summary-path `main_fuel_type` for non-gas/non-104 boilers (only 101–119 + the
+  existing liquid/solid/electric/community branches are covered).
+
+## Process notes
+- One slice = one commit, spec citation in the message, `Co-Authored-By: Claude
+  Opus 4.8` trailer. AAA tests, `abs(x-y) <= tol` (not `pytest.approx`).
+- The 4 sim-case e2e fixtures pin Block 1 (UK-avg rating) via
+  `Sap10Calculator().calculate(epc)` — NOT the postcode demand block.
+- Window ORIENTATION does NOT change the SAP rating much (+0.25 for 3.82 m²) — do
+  not over-attribute the 6035 gap to it.

domain/sap10_calculator/docs/HANDOVER_POST_S0380_200.md

@@ -0,0 +1,186 @@
+# Handover — post S0380.200 (dual-main split done; boiler-interlock −5pp OPEN)
+
+Point-in-time note. Start from [`AGENT_GUIDE.md`](AGENT_GUIDE.md) for methodology,
+accuracy bar, and pipeline — this records *what this session did* and *what is open*.
+
+- **Branch:** `feature/per-cert-mapper-validation`
+- **HEAD:** `8ae978a6` (S0380.200)
+- **Baseline:** `2355 passed, 1 skipped, 0 failed`. Verify with the AGENT_GUIDE §4 suite command.
+
+---
+
+## What this session shipped (S0380.196–200)
+
+The through-line: **golden certs 6035 and 0240 were both closed to SAP-exact**
+by finding real API-mapper bugs (not "lodged divergence"), each confirmed
+against a user-generated Elmhurst worksheet ("simulated case 5/6").
+
+| Slice | What | Spec |
+|---|---|---|
+| **.196** | API Simplified Type 1 room-in-roof: `room_in_roof_type_1` gables (length-only, no height) weren't deducted from the A_RR shell → whole shell billed as roof at U_RR=2.30 (+52 W/K). Route them through `detailed_surfaces` (gable area = L × 2.45 default RR storey height). **6035 SAP −2→+0 exact**, PE +19.16→+1.84. | RdSAP 10 §3.9.1(e) p.21; Table 4 p.22 |
+| **.197** | Promoted "simulated case 5" (detached sandstone RR) to e2e fixture (`001431_case5`, 11 pins @1e-4). Fixed sandstone wall label `"SS"`→2 (`_ELMHURST_WALL_CODE_TO_SAP10`) + `_parse_thickness_mm` for "400+ mm" roof insulation (trailing `+` was dropped → u_roof fell to age default). | — |
+| **.198** | **API `window_wall_type=4` → roof window.** These are roof-of-room rooflights; the mapper flattened them into `sap_windows` (vertical, (27), U=2.0) instead of `sap_roof_windows` ((27a), inclined U=2.30 + 45° solar). The inclined solar dominates → **0240 SAP −1→+0 exact**, PE +3.91→+1.95; 6035 PE +1.84→+1.37. Discriminator is `wall_type==4` NOT `window_type==2` (0390/7536 lodge window_type=2 on main walls). | SAP 10.2 §3 (27a); Table 6e Note 2 |
+| **.199** | Site-notes mirror of .198: extractor parses "Roof of Room" window rows (`_parse_window_from_anchors`); `_is_elmhurst_roof_window` location branch; `_ELMHURST_ROOF_WINDOW_U_BY_GLAZING["Double between 2002 and 2021"]=2.30`. Case 6 pinned on §3 windows (`test_section_3_roof_windows_case6_match_pdf`): (27)=22.7408, (27a)=13.0375 exact. | RdSAP 10 §3.7 |
+| **.200** | **SAP 10.2 §9a two-main-heating split** (203)/(204)/(205)/(207)/(213). The cascade lumped a 2-main dwelling into one system. Now `space_heating_fuel_monthly_kwh` splits demand (204) to sys1 @ (206) + (205) to sys2 @ (207); `_solve_month` sums main_1+main_2; `_main_heating_detail_efficiency` (new, the per-detail core of `_main_heating_efficiency`) gives each system its own efficiency. Site-notes: `_map_elmhurst_main_heating_2` inherits Main 1's fuel when §14.1 omits Fuel Type. Cost/CO2/PE main_2 paths were already wired. 0240 unchanged (identical Eq-D1 systems). | SAP 10.2 §9a |
+
+Two new e2e fixtures: `001431_case5` (full SapResult, S0380.197) and
+`001431_case6` (§3 windows only, S0380.199 — see why below). Source PDFs
+tracked under `sap worksheets/golden fixture debugging/simulated case {5,6}/`;
+Summaries mirrored to `backend/documents_parser/tests/fixtures/Summary_001431_case{5,6}.pdf`.
+
+---
+
+## ⚠️ CORRECTION (post S0380.201) — the interlock priority was ALREADY DONE
+
+The "priority" below was **misdiagnosed**. At HEAD the cascade already
+produces case 6 (206) sys-1 eff = **79.0** and (207) sys-2 eff = **84.0**,
+matching the worksheet exactly. The cylinder-thermostat interlock path
+(`no_stored_hw_interlock = has_cylinder and cylinder_thermostat != "Y"`)
+has existed since **S0380.141**; the room-thermostat path since S0380.177.
+`no_interlock = no_room_thermostat OR no_stored_hw_interlock` — it does NOT
+only catch 2101/2102. Toggling case 6 `cylinder_thermostat` N→Y flips eff
+0.79→0.84, confirming the −5pp fires. Golden **0240 is a combi**
+(`has_hot_water_cylinder=False`) → correctly NOT penalised; its predicted
+re-pin from the interlock is void. The misread came from
+`energy_requirements_section_from_cert` (a §2.4 debug helper using raw
+`_main_heating_efficiency`, which reports 84 — the real `cert_to_inputs`
+cascade applies the −5pp at ~line 6071). See [[feedback-verify-handover-claims]].
+
+**S0380.201 landed the SECONDARY item** (dual-system aux pumps): SAP 10.2
+Table 4f note c) second main-system circulation pump, gated on a lodged
+`main_heating_fraction > 0`. Case 6 (231) 241 → **356** EXACT (= 41 Main-1
+pump + 115 Main-2 pump + 200 oil aux). 0240 re-pinned (pumps 315 → 430,
+integer 73 → 72, resid +0 → -1, PE +2.8092, CO2 +0.1385) — anticipated
+and authorised below. 000565 protected by the fraction>0 gate (its Main 2
+is a DHW-only combi, fraction 0).
+
+**Remaining case-6 gaps for full-SapResult promotion** (vs P960-0001-001431):
+- (98c) space demand cascade **12145.31** vs ws **11991.96** (+1.28%) —
+  living-area MIT (87) ~0.3 °C low in winter; multi-causal (gains/heat-loss).
+- (219) hot water cascade **4824.74** vs ws **4902.86** (−1.6%) — §4 walk needed.
+Once both close, promote case 6 to a full SapResult e2e fixture (pin grid below).
+
+---
+
+## OPEN (was the priority, now DONE) — boiler-interlock −5pp efficiency adjustment, per main system
+
+**Goal:** a RdSAP-10/SAP-10.2 **spec-accurate** implementation of the boiler
+interlock efficiency adjustment, applied **per main heating system**, done in
+the established pattern of this domain (per-line walk → cite spec → TDD →
+re-pin). This is the last gap blocking full closure of simulated **case 6**,
+and it will also re-pin golden **0240**.
+
+### The evidence (simulated case 6)
+
+`sap worksheets/golden fixture debugging/simulated case 6/` — detached, dual
+**oil** boiler (both SAP code **127**, base seasonal eff **84%**), radiators 51%
+(control **2106**) + underfloor 49% (control **2110**). Its P960 worksheet:
+
+| line | worksheet | meaning |
+|---|---|---|
+| (206) main sys-1 eff | **79.0** | 84 − **5pp** |
+| (207) main sys-2 eff | **84.0** | base, no penalty |
+| (216) water-heater eff | **72.0** | also penalised (DHW leg of the −5pp) |
+| "Temperature adjustment" | 0.0000 | **flow temp has NO effect** — this is NOT a flow-temperature feature |
+
+Summary §14 lodges it explicitly: system 1 **"Boiler Interlock: No"**, system 2
+**"Boiler Interlock: Yes"**. The 84→79 is the SAP 10.2 **Table 4c(2)** "no boiler
+interlock" −5pp **Space + DHW** adjustment (same mechanism as the AGENT_GUIDE
+"oil 6" worked example, S0380.177 — but that one fired off control 2101).
+
+### Why control 2106 (which HAS a room thermostat) is "no interlock"
+
+Per RdSAP 10 boiler-interlock rules (find + cite the exact §; the existing
+`_NO_INTERLOCK_CONTROLS = {2101, 2102}` block in `cert_to_inputs.py` ~line 1238
+quotes "RdSAP 10 §3 p.57: boiler interlock is assumed present if there is a room
+thermostat and [time control], AND — when there is a hot-water cylinder — a
+cylinder thermostat; otherwise not interlocked"): system 1 serves the **DHW
+cylinder**, the cylinder is present (`Hot Water Cylinder Present: Yes`) but
+**`Cylinder Thermostat: No`** → interlock **not** present → −5pp, *despite* the
+room thermostat. System 2 (underfloor, separate part, no cylinder interaction)
+keeps interlock via its zone control → no penalty.
+
+So the determination is **not** "control ∈ {2101,2102}". It is, per system:
+`interlock present` ⇔ (room thermostat present, from the control code) AND
+(time/programmer control) AND (cylinder absent OR cylinder thermostat present).
+The current cascade only catches the "no room thermostat" path (2101/2102); it
+misses the "room thermostat present but no cylinder thermostat" path that 2106
+hits here.
+
+### This single root cause explains BOTH remaining case-6 deltas
+
+- space heating: sys-1 eff 79 not 84 → main fuel cascade 14925 vs ws **14736.96**
+- hot water: the −5pp DHW leg → cascade HW 4824 vs ws **4902.86** (lower cascade
+  fuel ⇒ cascade eff too high ⇒ missing the penalty)
+
+### 0240 will shift — and that is correct (apply the spec uniformly)
+
+Golden **0240** has the SAME controls (sys1 2106 / sys2 2110) AND the same
+`cylinder_thermostat = "N"` with a cylinder present. So the spec-correct rule
+applies the −5pp to 0240's system 1 too. 0240 is currently SAP-exact (continuous
+72.55) **without** the penalty — that is an offsetting coincidence (it's API-only,
+±0.5 bar, no worksheet). Per [[feedback-software-no-special-handling]] +
+[[feedback-spec-floor-skepticism]]: implement the spec rule, let 0240 shift, and
+**re-pin** it with a documented note. Expect 0240 continuous SAP to drop ~0.3–0.5
+(may take the integer 73→72; if so the golden `expected_sap_resid` moves −1 and
+that is the new truth). Measure precisely and re-pin PE/CO2 too.
+
+### Where to implement (per-line walk first, then TDD)
+
+1. **Interlock determination.** Add a per-`MainHeatingDetail` helper, e.g.
+   `_boiler_interlock_present(main, epc) -> bool`, encoding the RdSAP 10 rule
+   above (room thermostat from control code + cylinder-thermostat gate when a
+   cylinder is present). `epc.sap_heating.cylinder_thermostat` ("Y"/"N") and
+   `cylinder_size`/`hot_water_cylinder_present` are the cylinder signals. The
+   site-notes path already lodges `cylinder_thermostat` (mapper.py ~5183, string
+   "Y"/"N"); the API path lodges it on `sap_heating.cylinder_thermostat` (0240 =
+   "N").
+2. **Apply Table 4c(2) −5pp per system.** The existing −5pp lives near the
+   `_NO_INTERLOCK_CONTROLS` block — find how it currently adjusts the seasonal
+   efficiency for 2101/2102 and generalise it to fire on
+   `not _boiler_interlock_present(main, epc)`, applied inside
+   `_main_heating_detail_efficiency` so **each** main system gets its own
+   adjustment (sys1 −5, sys2 0). Confirm the DHW leg (water-heater efficiency
+   (216)) is penalised too — the §4 water-heating cascade reads
+   `_main_heating_efficiency`; verify the −5pp flows there (case 6 (216)=72
+   is the check).
+3. **Verify combi vs regular rows of Table 4c(2).** The "no interlock" −5pp has a
+   combi row (Space −5 / DHW 0) and a regular-boiler row (Space −5 / DHW −5);
+   the DHW leg is gated on cylinder presence. Case 6 is a regular oil boiler with
+   a cylinder → DHW −5 applies (hence (216)=72). Read the table; don't assume.
+
+### Validation target
+
+After the fix, **promote case 6 to a full SapResult e2e fixture** (it's currently
+§3-windows-only because the lumped efficiency made (211)/(219)/(231) non-
+comparable). Case 6 worksheet Block-1 pin grid (P960-0001-001431):
+- SAP 72 (258), continuous **71.6597**, ECF **2.0316** (257)
+- total fuel cost **1162.5374** (255), CO2 **5953.6679** (272)
+- (211) main sys-1 fuel **7741.6458**, (213) main sys-2 fuel **6995.3106**
+  (SapResult.main_heating_fuel_kwh_per_yr should be the sum **14736.9564**)
+- hot water **4902.8601** (219), lighting **357.6571** (232)
+- pumps/fans **356.0** (231) — **see the SECOND open item below**
+
+### SECONDARY open item — dual-system auxiliary pumps (Table 4f)
+
+Case 6 (231) = **356** = (230c) central-heating pump 156 + (230d) oil-boiler pump
+200. Cascade gives **241**. Two boilers → two pump contributions per Table 4f
+(note c: "where there are two main heating systems include two figures from this
+table" — same note already used for the 0240 oil-pump in S0380.148). Needs the
+per-system pump aggregation. Smaller than the interlock fix; do it after, then
+case 6's (231) pin closes and the full e2e fixture lands.
+
+---
+
+## Process notes
+- One slice = one commit, spec citation (page + line) in the message,
+  `Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>` trailer.
+- AAA tests (`# Arrange/# Act/# Assert`), `abs(x-y) <= tol` (not `pytest.approx`).
+- New code passes `pyright` strict, 0 errors. (mapper.py + cert_to_inputs.py each
+  carry **32 pre-existing** errors — don't add to them; check with a `git stash`
+  baseline comparison.)
+- The Elmhurst worksheet is ground truth at abs=1e-4. 0240 is API-only (±0.5
+  fallback) — case 6 is its worksheet-backed proxy for the heating archetype, but
+  differs from 0240 on the boiler SAP code (127 vs 0240's 130 condensing combi),
+  so pin case 6 to ITS OWN worksheet, not 0240's register.
+- Suite command + section/e2e harness layout: AGENT_GUIDE §2.6 + §4.

domain/sap10_calculator/rdsap/cert_to_inputs.py

@@ -164,7 +164,10 @@ from domain.sap10_calculator.worksheet.energy_requirements import (
 from domain.sap10_calculator.worksheet.fabric_energy_efficiency import (
     fabric_energy_efficiency_kwh_per_m2_yr,
 )
-from domain.sap10_calculator.worksheet.photovoltaic import pv_split_monthly
+from domain.sap10_calculator.worksheet.photovoltaic import (
+    PhotovoltaicSplit,
+    pv_split_monthly,
+)
 from domain.sap10_calculator.worksheet.space_cooling import (
     SpaceCoolingResult,
     space_cooling_monthly_kwh,
@@ -659,6 +662,19 @@ _INSTANTANEOUS_WATER_CODES: Final[frozenset[int]] = frozenset({907, 909})
 # zero-loss list, so primary loss is zero whenever this code is lodged.
 _WHC_ELECTRIC_IMMERSION: Final[int] = 903
 
+# Water-heating codes for a dedicated "boiler/circulator for water
+# heating only" — SAP 10.2 Table 4a hot-water section (PDF p.166):
+# 911 gas, 912 liquid fuel, 913 solid fuel boiler/circulator; 921-931
+# range cooker with boiler for water heating only. Each is a heat
+# generator feeding the cylinder through a primary loop, so SAP 10.2
+# Table 3 (PDF p.160) row 1 primary circuit loss applies — independent
+# of the space-heating system (which for these certs is a separate main,
+# e.g. electric storage heaters). 941 (electric HP for water only) is
+# excluded: HP DHW vessels follow the Table 3 integral-vessel rules.
+_WATER_HEATING_BOILER_CIRCULATOR_CODES: Final[frozenset[int]] = frozenset(
+    {911, 912, 913} | set(range(921, 932))
+)
+
 
 # SAP 10.2 Appendix M equation (M1): EPV = 0.8 × kWp × S × ZPV, summed
 # per array. The module efficiency constant (0.8), orientation-dependent
@@ -883,6 +899,12 @@ _HEAT_NETWORK_HEAT_SOURCE_EFFICIENCY: Final[dict[int, float]] = {
     304: 3.00,
 }
 
+# SAP 10.2 Table 12 (PDF p.191) "Heat networks" standing charge row =
+# £120/yr (note (k)). Note (l): "Include half this value if only DHW is
+# provided by a heat network." §C3.2 (PDF p.58): the full charge applies
+# when the space heating is also on the heat network.
+_HEAT_NETWORK_STANDING_CHARGE_GBP: Final[float] = 120.0
+
 
 def _is_heat_network_main(main: Optional[MainHeatingDetail]) -> bool:
     """True when the cert's main heating is a heat network — either by
@@ -1479,6 +1501,35 @@ def _water_heating_main(
     return details[0]
 
 
+def _water_heating_main_space_fraction(
+    epc: EpcPropertyData, secondary_fraction: float
+) -> float:
+    """Fraction of TOTAL space heating provided by the DHW boiler — the
+    SAP 10.2 Appendix D §D2.1(2) Equation D1 Q_space weight.
+
+    Eq D1's monthly water-heater efficiency blends η_winter / η_summer by
+    the ratio of the boiler's space-heating load to its water load. On a
+    single-main / WHC-901 cert that load is the whole main share,
+    (202) = 1 − (201). On a dual-main cert the DHW boiler does ONLY its
+    own share — (204) for Main 1, (205) for Main 2 — so feeding it the
+    dwelling total over-weights η_winter and under-states HW fuel
+    (simulated case 6: Main 1 serves DHW + 51% of space heat; using 100%
+    of demand gave HW −78 kWh vs the worksheet)."""
+    details = epc.sap_heating.main_heating_details if epc.sap_heating else []
+    main_fraction = 1.0 - secondary_fraction  # (202)
+    if len(details) < 2:
+        return main_fraction
+    main_2 = details[1]
+    main_2_of_main = (
+        main_2.main_heating_fraction / 100.0
+        if main_2.main_heating_fraction is not None
+        else 0.0
+    )
+    if _water_heating_main(epc) is details[1]:
+        return main_fraction * main_2_of_main  # (205) — DHW from Main 2
+    return main_fraction * (1.0 - main_2_of_main)  # (204) — DHW from Main 1
+
+
 def _rdsap_tariff(epc: EpcPropertyData) -> Tariff:
     """Resolve the cert's Table 12a tariff column via RdSAP 10 §12
     Rules 1-4 (page 62). Consults BOTH main heating systems — §12
@@ -1563,6 +1614,35 @@ def _is_community_heating_hw_from_main(epc: EpcPropertyData) -> bool:
     )
 
 
+def _heat_network_standing_charge_gbp(
+    epc: EpcPropertyData, main: Optional[MainHeatingDetail]
+) -> Optional[float]:
+    """SAP 10.2 Table 12 note (l) + §C3.2 heat-network standing charge, or
+    None when the dwelling is not on a heat network (caller then falls back
+    to the fuel-based `additional_standing_charges_gbp`).
+
+    A heat network carries the Table 12 £120/yr standing charge regardless
+    of the network fuel — full when the SPACE heating is on the network
+    (§C3.2 "the total standing charge is the normal heat network standing
+    charge"), halved to £60 when ONLY DHW is provided by the heat network
+    (note (l)). This REPLACES the fuel-based gas/off-peak standing for a
+    heat-network main, so it must not be added on top of
+    `additional_standing_charges_gbp` (which would double-count: a
+    Summary-path community-gas main lodges Table-32 code 1 and already
+    draws the £120 gas standing). Worksheet-validated: simulated case 14
+    (community boilers + mains gas, space + water) → (351) = £120.
+
+    The API path under-counted this: an EPC community fuel (e.g. 20 = mains
+    gas community) is not a Table-32 gas code, so `_is_gas_code` returned
+    False and the standing came out £0 — cert 9390 lost the whole £120.
+    """
+    if _is_heat_network_main(main):
+        return _HEAT_NETWORK_STANDING_CHARGE_GBP
+    if _is_community_heating_hw_from_main(epc):
+        return _HEAT_NETWORK_STANDING_CHARGE_GBP / 2.0
+    return None
+
+
 def _main_heating_efficiency(epc: EpcPropertyData) -> float:
     """SAP 10.2 (206) main system 1 efficiency as a 0..1 fraction.
 
@@ -1570,7 +1650,16 @@ def _main_heating_efficiency(epc: EpcPropertyData) -> float:
     seasonal efficiency → heat-network 1/DLF override. Used by §4 (water
     heating cascade) and §9a (per-system fuel kWh) — both must see the
     same value, so this single helper is the single source of truth."""
-    main = _first_main_heating(epc)
+    return _main_heating_detail_efficiency(_first_main_heating(epc), epc)
+
+
+def _main_heating_detail_efficiency(
+    main: Optional[MainHeatingDetail], epc: EpcPropertyData
+) -> float:
+    """SAP 10.2 (206)/(207) efficiency (0..1) for a SPECIFIC main heating
+    detail — the per-detail core of `_main_heating_efficiency`. Used for
+    both main system 1 (206) and main system 2 (207) on dual-main certs
+    (cert 0240 / simulated case 6)."""
     main_code = main.sap_main_heating_code if main is not None else None
     main_category = main.main_heating_category if main is not None else None
     main_fuel = _main_fuel_code(main)
@@ -1817,6 +1906,37 @@ def _main_fuel_code(main: Optional[MainHeatingDetail]) -> Optional[int]:
     raise MissingMainFuelType(fuel, main.sap_main_heating_code)
 
 
+def _heat_network_factor_fuel_code(
+    main: Optional[MainHeatingDetail],
+) -> Optional[int]:
+    """Fuel code to feed the Table 12 / Table 32 factor lookups, with the
+    EPC→Table-12 translation applied for heat-network (community) mains.
+
+    The EPC `main_fuel_type` enum and the SAP Table 12 / Table 32 fuel-code
+    numbering COLLIDE in the 18-25 range: `epc_codes.csv` lists
+    20='mains gas (community)', 21='LPG (community)', 22='oil (community)',
+    ..., whereas Table 12/32 code 20-25 are solid biomass fuels. The factor
+    lookups (`co2_factor_kg_per_kwh` / `primary_energy_factor` /
+    `unit_price_p_per_kwh`) check the Table-12/32 dict FIRST, so an EPC
+    community fuel 20 silently returns the biomass factor (CO2 0.028, PE
+    1.046, wood-logs price) instead of community mains gas (CO2 0.210, PE
+    1.130, mains-gas price + £120 standing charge).
+
+    Resolution: for a heat-network main, translate the EPC community fuel to
+    its Table-12 code via `API_FUEL_TO_TABLE_12` (20->51) so the lookups hit
+    the heat-network row. NON-heat-network mains are returned unchanged so a
+    genuine biomass boiler (EPC 6 wood logs / 12 biomass, etc.) keeps its raw
+    Table-12 factor. The Summary path is unaffected — it maps
+    "Mains gas - community" to code 1 (no collision). Worksheet-validated:
+    simulated case 14 (community boilers + mains gas, SAP code 301) →
+    (367) CO2 factor 0.2100, (467) PE factor 1.1300.
+    """
+    fuel = _main_fuel_code(main)
+    if fuel is None or not _is_heat_network_main(main):
+        return fuel
+    return API_FUEL_TO_TABLE_12.get(fuel, fuel)
+
+
 def _fuel_cost_gbp_per_kwh(
     main: Optional[MainHeatingDetail], prices: PriceTable
 ) -> float:
@@ -1844,7 +1964,10 @@ def _fuel_cost_gbp_per_kwh(
         )
         blended_p = chp_frac * chp_price + (1.0 - chp_frac) * boiler_price
         return blended_p * _PENCE_TO_GBP
-    return prices.unit_price_p_per_kwh(_main_fuel_code(main)) * _PENCE_TO_GBP
+    return (
+        prices.unit_price_p_per_kwh(_heat_network_factor_fuel_code(main))
+        * _PENCE_TO_GBP
+    )
 
 
 # RdSAP energy_tariff enum (per datatypes/epc/domain/epc_codes.csv):
@@ -1962,23 +2085,6 @@ def _off_peak_low_rate_gbp_per_kwh(tariff: Tariff) -> float:
     return low * _PENCE_TO_GBP
 
 
-def _off_peak_low_rate_gbp_per_kwh_via_meter_heuristic(meter_type: object) -> float:
-    """Off-peak low-rate £/kWh for callsites that detect off-peak via the
-    `_is_off_peak_meter` heuristic (RdSAP meter code 3 = Unknown is
-    treated as off-peak for electric end-uses; see _is_off_peak_meter
-    docstring). When the meter resolves to a known off-peak tariff
-    (codes 1/4/5), bills at that tariff's Table 32 low rate; when the
-    meter resolves to STANDARD (codes 2 = Single, 3 = Unknown), falls
-    back to the SEVEN_HOUR rate (5.50, Table 32 code 31). Codifies the
-    heuristic that pre-S0380.138 was baked into the literal
-    `prices.e7_low_rate_p_per_kwh` constant."""
-    tariff = tariff_from_meter_type(meter_type)
-    if tariff is Tariff.STANDARD:
-        _high, low = _tariff_high_low_rates_p_per_kwh(Tariff.SEVEN_HOUR)
-        return low * _PENCE_TO_GBP
-    return _off_peak_low_rate_gbp_per_kwh(tariff)
-
-
 # Tariff → (high_rate_fuel_code, low_rate_fuel_code) for the SAP 10.2
 # Table 12d (CO2) / Table 12e (PE) monthly factors. Mirror of the
 # Table 32 cost-rates dict above: 7-hour and 10-hour tariffs split into
@@ -2018,6 +2124,16 @@ def _table_12a_system_for_main(
         main.main_heating_index_number is not None
         and heat_pump_record(main.main_heating_index_number) is not None
     )
+    # Electric room heaters (RdSAP main_heating_category 10) are direct-
+    # acting electric → SAP 10.2 Table 12a Grid 1 (PDF p.191) "Other
+    # systems including direct-acting electric" row (7-hour high-rate
+    # fraction 1.00, 10-hour 0.50). Distinct from electric STORAGE
+    # heaters (category 7), which charge off-peak and correctly fall
+    # through to None here (→ 100% low rate). Gated on `_is_electric_main`
+    # so a non-electric room heater (gas / solid-fuel cat 10) is excluded;
+    # all callers already pre-gate on electric, this is belt-and-braces.
+    if main.main_heating_category == 10 and _is_electric_main(main):
+        return Table12aSystem.OTHER_DIRECT_ACTING_ELECTRIC
     # ASHP — Table 4a rows 211-217 (earlier generations) + 221-227
     # (2013+) cover the air-source space. Warm-air ASHPs are 521-524.
     if code is not None and (
@@ -2053,6 +2169,41 @@ def _space_heating_fuel_cost_gbp_per_kwh(
     return blended * _PENCE_TO_GBP
 
 
+def _main_space_heating_high_rate_fraction(
+    main: Optional[MainHeatingDetail],
+    tariff: Tariff,
+) -> float:
+    """SAP 10.2 Appendix M1 §3a (PDF p.93) — the fraction of the main
+    space-heating fuel that is billed at the HIGH rate in Section 10a,
+    i.e. carries an "electricity not at the low-rate" fuel code (30, 32,
+    34, 35 or 38). Only this high-rate portion of E_space,m may enter the
+    PV-eligible demand D_PV,m; the low-rate portion (code 31/33/36/37/39)
+    is excluded.
+
+    Mirrors `_space_heating_fuel_cost_gbp_per_kwh`'s rate split exactly so
+    the D_PV inclusion and the §10a billing stay consistent:
+      - non-electric main, or STANDARD tariff → 1.0 (no off-peak split;
+        the eligible-code gate in `_pv_eligible_demand_monthly_kwh`
+        already excludes non-electric fuels, and a STANDARD-tariff
+        electric main bills 100% at code 30).
+      - electric main on an off-peak tariff whose Table 12a Grid 1 SH row
+        is wired → the published high-rate fraction. Electric STORAGE
+        heaters (Table 12a `_table_12a_system_for_main` → None, charged
+        wholly off-peak) and any system whose Grid 1 SH row is not yet
+        wired bill 100% at the low rate → fraction 0.0, so E_space,m is
+        excluded from D_PV entirely (worksheet (240) high-rate cost = 0).
+    """
+    if not _is_electric_main(main) or tariff is Tariff.STANDARD:
+        return 1.0
+    system = _table_12a_system_for_main(main)
+    if system is None:
+        return 0.0
+    try:
+        return space_heating_high_rate_fraction(system, tariff)
+    except NotImplementedError:
+        return 0.0
+
+
 def _hot_water_fuel_cost_gbp_per_kwh(
     water_heating_fuel: Optional[int],
     main: Optional[MainHeatingDetail],
@@ -2155,6 +2306,35 @@ def _secondary_efficiency(
     return seasonal_efficiency(code, None, None)
 
 
+def _secondary_off_peak_rate_gbp_per_kwh(meter_type: object) -> float:
+    """SAP 10.2 Table 12a Grid 1 (PDF p.191) blended rate for an electric
+    secondary heater on an off-peak tariff. The secondary is a direct-
+    acting electric room heater (RdSAP 10 §A.2.2 default), so it sits on
+    the "Other systems including direct-acting electric" row — high-rate
+    fraction 1.00 for 7-hour, 0.50 for 10-hour. NOT the 100%-low-rate of
+    storage-charging: a room heater runs on demand, mostly at the high
+    rate. Worksheet evidence — simulated case 19 (242): "Space heating -
+    secondary (1.00*15.29 + 0.00*5.50)" → all at the 7-hour HIGH rate.
+
+    Mirrors `_space_heating_fuel_cost_gbp_per_kwh`: the meter resolves to
+    a tariff (the `_is_off_peak_meter` Unknown-code-3 heuristic falls
+    through to 7-hour, as in `_off_peak_low_rate_gbp_per_kwh_via_meter_
+    heuristic`); 18-/24-hour tariffs (absent from the Grid 1 direct-acting
+    row) fall back to the tariff's Table 32 low rate."""
+    tariff = tariff_from_meter_type(meter_type)
+    if tariff is Tariff.STANDARD:
+        tariff = Tariff.SEVEN_HOUR
+    try:
+        high_frac = space_heating_high_rate_fraction(
+            Table12aSystem.OTHER_DIRECT_ACTING_ELECTRIC, tariff,
+        )
+    except NotImplementedError:
+        return _off_peak_low_rate_gbp_per_kwh(tariff)
+    high_rate, low_rate = _tariff_high_low_rates_p_per_kwh(tariff)
+    blended = high_frac * high_rate + (1.0 - high_frac) * low_rate
+    return blended * _PENCE_TO_GBP
+
+
 def _secondary_fuel_cost_gbp_per_kwh(
     sap_heating,
     main: Optional[MainHeatingDetail],
@@ -2170,13 +2350,13 @@ def _secondary_fuel_cost_gbp_per_kwh(
         # Default to electricity since the default secondary system is
         # portable electric heaters (code 693).
         if _is_off_peak_meter(meter_type, fuel_is_electric=True):
-            return _off_peak_low_rate_gbp_per_kwh_via_meter_heuristic(meter_type)
+            return _secondary_off_peak_rate_gbp_per_kwh(meter_type)
         return prices.standard_electricity_p_per_kwh * _PENCE_TO_GBP
     # When secondary_fuel_type is electricity, apply off-peak if applicable.
     if _is_electric_water(sec_fuel) and _is_off_peak_meter(
         meter_type, fuel_is_electric=True
     ):
-        return _off_peak_low_rate_gbp_per_kwh_via_meter_heuristic(meter_type)
+        return _secondary_off_peak_rate_gbp_per_kwh(meter_type)
     return prices.unit_price_p_per_kwh(sec_fuel) * _PENCE_TO_GBP
 
 
@@ -2315,6 +2495,7 @@ def _pv_eligible_demand_monthly_kwh(
     main_fuel_code_table_12: Optional[int],
     secondary_fuel_code_table_12: Optional[int],
     water_heating_fuel_code_table_12: Optional[int],
+    main_space_high_rate_fraction: float = 1.0,
 ) -> tuple[float, ...]:
     """SAP 10.2 Appendix M1 §3a (p.93) — monthly PV-eligible demand
     D_PV,m. Always includes lighting + appliances + cooking + electric
@@ -2323,6 +2504,18 @@ def _pv_eligible_demand_monthly_kwh(
     (codes 30, 32, 34, 35, 38 per spec). Includes E_water,m only when
     the water heating fuel code is 30 (standard electricity) per spec.
 
+    `main_space_high_rate_fraction` scales the main-heating contribution
+    by the portion billed at the HIGH rate (code 30) in Section 10a.
+    Per the §3a inclusion rule "(211) should be included only where the
+    fuel code applied to it in Section 10a is 30, 32, 34, 35 or 38 (i.e.
+    electricity not at the low-rate)", off-peak electric mains (e.g.
+    storage heaters charged wholly at the low rate, fraction 0.0) must
+    NOT add their (211) to D_PV. Defaults to 1.0 → unchanged for
+    STANDARD-tariff electric mains and the gas-main / electric-secondary
+    cohort. Without this, off-peak storage-heater dwellings over-counted
+    D_PV by the full (211) in winter, inflating R_PV,m → β → the onsite
+    PV split (case 19: β_Jan 0.894 → 0.792, matching worksheet 0.791).
+
     Secondary space heating is included on the same footing as main:
     Appendix M1 §3a counts E_space,m as the dwelling's total electric
     space-heating demand, which for a gas-main / electric-secondary
@@ -2332,9 +2525,13 @@ def _pv_eligible_demand_monthly_kwh(
     worksheet (233a) gap localised on the cohort-2 gas+PV certs:
     cert 3136 onsite 726.9 → 790.3 vs worksheet 792.1).
 
-    The off-peak immersion × (243) Ewater branch and the Appendix G4
-    PV diverter adjustment are deferred — current cohort fixtures
-    don't exercise them."""
+    The off-peak immersion × (243) Ewater branch is deferred. The
+    Appendix G4 PV-diverter saving is intentionally NOT reflected here:
+    per the §3a note (PDF p.93, lines 5485-5486) "If there is a PV
+    diverter, then for the purposes of this β factor calculation (219)m
+    should not include the diverter savings" — so D_PV uses the
+    pre-diverter (219), and the diverter (63b)m is applied afterwards in
+    `_pv_diverter_monthly_kwh`."""
     include_main_space = (
         main_fuel_code_table_12 is not None
         and main_fuel_code_table_12 in _PV_ELIGIBLE_SPACE_HEATING_FUEL_CODES
@@ -2357,7 +2554,7 @@ def _pv_eligible_demand_monthly_kwh(
             + pumps_fans_monthly_kwh[m]
         )
         if include_main_space:
-            d += main_1_fuel_monthly_kwh[m]
+            d += main_space_high_rate_fraction * main_1_fuel_monthly_kwh[m]
         if include_secondary_space:
             d += secondary_fuel_monthly_kwh[m]
         if include_water:
@@ -2366,6 +2563,70 @@ def _pv_eligible_demand_monthly_kwh(
     return tuple(monthly)
 
 
+# SAP 10.2 Appendix G4 step 4 (PDF p.73) — correction factors applied to
+# the surplus PV available to the diverter: 0.8 for the cylinder's
+# ability to accept the heat, and fPV,diverter,storageloss = 0.9 for the
+# increased cylinder losses from storing water at a higher temperature.
+_PV_DIVERTER_CYLINDER_ACCEPTANCE_FACTOR: Final[float] = 0.8
+_PV_DIVERTER_STORAGE_LOSS_FACTOR: Final[float] = 0.9
+
+
+def _pv_diverter_monthly_kwh(
+    *,
+    epc: EpcPropertyData,
+    pv_export_monthly_kwh: tuple[float, ...],
+    water_demand_monthly_kwh: tuple[float, ...],
+    avg_daily_hot_water_l: float,
+    battery_capacity_kwh: float,
+    pv_generation_kwh: float,
+) -> Optional[tuple[float, ...]]:
+    """SAP 10.2 Appendix G4 (PDF p.72-73) — monthly PV-diverter water-
+    heating input SPV,diverter,m (positive kWh), entered as the negative
+    worksheet (63b)m.
+
+    `pv_export_monthly_kwh` is the pre-diverter surplus EPV,m × (1 − βm)
+    — the portion of PV generation not consumed by the dwelling's
+    instantaneous demand, which would otherwise be exported. Per G4 step
+    4:
+
+        SPV,diverter,m = EPV,m × (1 − βm) × 0.8 × fPV,diverter,storageloss
+
+    clamped to ≤ (62)m + (63a)m (`water_demand_monthly_kwh`; (63a) the
+    WWHRS reduction, 0 here) so the diverter never supplies more than the
+    water-heating demand.
+
+    Returns None — diverter disregarded by software (G4 step 1) — unless
+    ALL four inclusion conditions hold:
+      a. a PV system connected to the dwelling supply (EPV > 0);
+      b. a cylinder whose volume exceeds (43) the average daily hot-water
+         use;
+      c. no solar water heating present;
+      d. no battery storage present.
+    `pv_diverter_present` (Summary §19 / API `pv_diverter`) gates the
+    whole calculation: an absent diverter returns None immediately.
+    """
+    if not epc.sap_energy_source.pv_diverter_present:
+        return None
+    # a. PV connected to the dwelling (case "a" Appendix M1 step 2).
+    if pv_generation_kwh <= 0.0:
+        return None
+    # b. Cylinder volume (litres) must exceed (43) average daily HW use.
+    cylinder_volume_l = _hot_water_cylinder_volume_l(epc)
+    if cylinder_volume_l is None or cylinder_volume_l <= avg_daily_hot_water_l:
+        return None
+    # c. No solar water heating. d. No battery storage.
+    if epc.solar_water_heating or battery_capacity_kwh > 0.0:
+        return None
+    correction = (
+        _PV_DIVERTER_CYLINDER_ACCEPTANCE_FACTOR
+        * _PV_DIVERTER_STORAGE_LOSS_FACTOR
+    )
+    return tuple(
+        min(pv_export_monthly_kwh[m] * correction, water_demand_monthly_kwh[m])
+        for m in range(12)
+    )
+
+
 # RdSAP 10 §11.1 b): when the kWp is not lodged but the cert lodges a
 # "% of roof area" PV figure, derive the PV peak power as
 # `0.12 × PV area`, with PV area being the dwelling's roof area for
@@ -2453,30 +2714,25 @@ def _pv_export_credit_gbp_per_kwh() -> float:
 
 
 def _pv_dwelling_import_price_gbp_per_kwh(
-    meter_type: object, prices: PriceTable
+    tariff: Tariff, prices: PriceTable
 ) -> float:
     """PV dwelling-consumption price per kWh per SAP 10.2 Appendix M1 §6
-    (p.94): "apply the normal import electricity price to PV energy used
-    within the dwelling". Onsite-consumed PV displaces grid IMPORTS, so
-    it bills at the standard electricity import tariff (Table 32 code 30
-    under the RdSAP10 amendment per ADR-0010 §10 = 13.19 p/kWh — the
-    same rate `_fuel_cost`'s `other_uses_p_per_kwh` already pays for
-    lighting/pumps/fans, and crucially the same rate Table 32 code 60
-    pays for the EXPORT credit. In Table 32 these collapse to a single
-    13.19 p value, so the IMPORT/EXPORT split is mathematically
-    equivalent to the legacy single-rate-EXPORT credit — but the
-    distinction matters when an off-peak tariff lands: §6 then directs
-    a weighted Table 12a high/low rate, deferred until the first off-
-    peak cost cert ships."""
-    if _is_off_peak_meter(meter_type, fuel_is_electric=True):
-        # Off-peak weighted Table 12a rate (deferred — `_fuel_cost`
-        # short-circuits Tariff != STANDARD before reaching this path).
-        # Routes through the meter-heuristic helper so an Unknown-meter
-        # cert (code 3 = "treat as off-peak for electric end-uses" per
-        # _is_off_peak_meter) falls back to the SEVEN_HOUR low rate
-        # rather than raising on STANDARD.
-        return _off_peak_low_rate_gbp_per_kwh_via_meter_heuristic(meter_type)
-    return table_32_unit_price_p_per_kwh(30) * _PENCE_TO_GBP
+    (PDF p.94, lines 5510-5513): "apply the normal import electricity
+    price to PV energy used within the dwelling … In the case of the
+    former, use a weighted average of high and low rates (Table 12a)."
+
+    Onsite-consumed PV displaces the dwelling's "all other uses"
+    electricity (lighting / appliances / pumps), so it bills at the same
+    Table 12a Grid 2 ALL_OTHER_USES rate `_other_fuel_cost_gbp_per_kwh`
+    derives — a STANDARD-tariff dwelling pays the flat Table 32 code 30
+    13.19 p/kWh (unchanged from the legacy single-rate path), while an
+    off-peak dwelling pays the weighted high/low blend (7-hour:
+    0.90 × 15.29 + 0.10 × 5.50 = 14.311 p/kWh, matching worksheet
+    (252)/(269) "PV used in dwelling" on case 19).
+
+    Pre-S0380.233 the off-peak branch returned the bare low rate
+    (5.50 p/kWh), under-crediting onsite PV on every off-peak cert."""
+    return _other_fuel_cost_gbp_per_kwh(tariff, prices)
 
 
 def _other_fuel_cost_gbp_per_kwh(
@@ -2778,7 +3034,7 @@ def _main_heating_co2_factor_kg_per_kwh(
             )
             if monthly is not None:
                 return monthly * scaling
-        return _co2_factor_kg_per_kwh(main) * scaling
+        return co2_factor_kg_per_kwh(_heat_network_factor_fuel_code(main)) * scaling
     if tariff is Tariff.STANDARD:
         monthly = _effective_monthly_co2_factor(
             main_fuel_monthly_kwh, _STANDARD_ELECTRICITY_FUEL_CODE,
@@ -2857,7 +3113,7 @@ def _main_heating_primary_factor(
             )
             if monthly is not None:
                 return monthly * scaling
-        return primary_energy_factor(fuel) * scaling
+        return primary_energy_factor(_heat_network_factor_fuel_code(main)) * scaling
     if tariff is Tariff.STANDARD:
         monthly = _effective_monthly_pe_factor(
             main_fuel_monthly_kwh, _STANDARD_ELECTRICITY_FUEL_CODE,
@@ -3133,7 +3389,7 @@ def _hot_water_co2_factor_kg_per_kwh(
             )
             if monthly is not None:
                 return monthly * scaling
-        return _co2_factor_kg_per_kwh(main) * scaling
+        return co2_factor_kg_per_kwh(_heat_network_factor_fuel_code(main)) * scaling
     fuel = _water_heating_fuel_code(epc)
     if fuel is None:
         return _DEFAULT_CO2_KG_PER_KWH
@@ -3197,7 +3453,7 @@ def _hot_water_primary_factor(
             )
             if monthly is not None:
                 return monthly * scaling
-        return primary_energy_factor(_main_fuel_code(main)) * scaling
+        return primary_energy_factor(_heat_network_factor_fuel_code(main)) * scaling
     fuel = _water_heating_fuel_code(epc)
     if fuel is None:
         return _DEFAULT_PEF
@@ -3956,11 +4212,25 @@ def energy_requirements_section_from_cert(
         if secondary_fraction_value > 0.0 else 0.0
     )
     eff = _main_heating_efficiency(epc)
+    # SAP 10.2 §9a two-main split (203)/(207): when a second main heating
+    # system is lodged, (203) = its `main_heating_fraction` (% of main
+    # heating it supplies) and (207) = its own seasonal efficiency. Cert
+    # 0240 (2× oil code 130, 51/49) + simulated case 6 (oil code 127,
+    # rads 51% + underfloor 49%) exercise this.
+    details = epc.sap_heating.main_heating_details if epc.sap_heating else []
+    main_2 = details[1] if len(details) >= 2 else None
+    main_2_of_main_fraction = 0.0
+    main_2_efficiency_value = 0.0
+    if main_2 is not None and main_2.main_heating_fraction is not None:
+        main_2_of_main_fraction = main_2.main_heating_fraction / 100.0
+        main_2_efficiency_value = _main_heating_detail_efficiency(main_2, epc)
     return space_heating_fuel_monthly_kwh(
         space_heating_monthly_kwh=sh.total_space_heating_monthly_kwh,
         secondary_heating_fraction=secondary_fraction_value,
         main_heating_efficiency_pct=eff * 100.0,
         secondary_heating_efficiency_pct=secondary_efficiency_value * 100.0,
+        main_2_of_main_fraction=main_2_of_main_fraction,
+        main_2_efficiency_pct=main_2_efficiency_value * 100.0,
     )
 
 
@@ -4103,13 +4373,27 @@ def _has_suspended_timber_floor_per_spec(
     if age in _AGE_BANDS_F_TO_M:
         return True, True  # sealed
     if age in _AGE_BANDS_A_TO_E:
-        # (a) U-value < 0.5 → sealed
-        main_floor_u = _main_floor_u_value(epc)
-        if main_floor_u is not None and main_floor_u < _FLOOR_U_SEALED_THRESHOLD:
-            return True, True
-        # (b) retro-fitted insulation + no U-value supplied → sealed
-        ins_type_str = (main.floor_insulation_type_str or "").strip().lower()
         u_value_known = bool(getattr(main, "floor_u_value_known", False))
+        # (a) a SUPPLIED floor U-value < 0.5 → sealed. RdSAP 10 §5 (PDF
+        # p.29) splits (a)/(b) on whether a U-value is supplied: (a) is
+        # the "U-value supplied" branch, (b) the "no U-value is supplied"
+        # branch. A computed default U (an assumed / as-built uninsulated
+        # floor) is NOT a supplied value, so it must NOT trigger (a) — it
+        # falls through to (b). Without this gate the cascade marked an
+        # as-built suspended-timber floor with default U=0.43 "sealed"
+        # (0.1) where Elmhurst uses "unsealed" (0.2) — cert 001431 sim
+        # case 2 worksheet (12)=0.2, dropping (25) effective ACH and
+        # understating space heating ~450 kWh.
+        main_floor_u = _main_floor_u_value(epc)
+        if (
+            u_value_known
+            and main_floor_u is not None
+            and main_floor_u < _FLOOR_U_SEALED_THRESHOLD
+        ):
+            return True, True
+        # (b) no U-value supplied: retro-fitted insulation → sealed;
+        # otherwise unsealed.
+        ins_type_str = (main.floor_insulation_type_str or "").strip().lower()
         if "retro" in ins_type_str and not u_value_known:
             return True, True
         # otherwise → unsealed
@@ -4447,6 +4731,27 @@ _CYLINDER_SIZE_CODE_TO_LITRES: Final[dict[int, float]] = {
 # from the ASHP cohort (all 7 certs lodge code 1, worksheet shows
 # "Foam" → factory-applied per SAP 10.2 Table 2 Note 2).
 _CYLINDER_INSULATION_TYPE_FACTORY: Final[int] = 1
+# RdSAP 10 field 7-11 (cylinder insulation type) — code 2 = loose jacket,
+# which SAP 10.2 Table 2 Note 1 gives a SEPARATE (higher) loss factor
+# L = 0.005 + 1.76 / (t + 12.8) vs the factory L = 0.005 + 0.55 / (t+4).
+_CYLINDER_INSULATION_TYPE_LOOSE_JACKET: Final[int] = 2
+
+
+def _cylinder_storage_loss_insulation_label(
+    insulation_type: "int | str | None",
+) -> Optional[Literal["factory_insulated", "loose_jacket"]]:
+    """Map the lodged cylinder_insulation_type code to the SAP 10.2
+    Table 2 loss-factor branch. Code 1 → factory-insulated, code 2 →
+    loose jacket. Any other value (None / 0 / unknown) → None so the
+    caller keeps the conservative no-storage-loss default rather than
+    guessing a loss branch. Accepts the int / digit-string / None shapes
+    `cylinder_insulation_type` arrives in across the two front-ends."""
+    code = _int_or_none(insulation_type)
+    if code == _CYLINDER_INSULATION_TYPE_FACTORY:
+        return "factory_insulated"
+    if code == _CYLINDER_INSULATION_TYPE_LOOSE_JACKET:
+        return "loose_jacket"
+    return None
 
 # RdSAP 10 §10.7 (PDF p.55) "No water heating system": SAP water-heating
 # code 999 (Elmhurst §15.0 "NON") signals that no DHW system was
@@ -4460,11 +4765,25 @@ _WHC_NO_WATER_HEATING_SYSTEM: Final[int] = 999
 # "Immersion Heater Type: Single" so the single-immersion path is used.
 _CYLINDER_SIZE_CODE_NORMAL_110L: Final[int] = 2
 # RdSAP 10 Table 29 (PDF p.56) "Hot water cylinder insulation if not
-# accessible" — the §10.7 default cylinder uses the age-band insulation,
-# same rule as the inaccessible-cylinder path: A-F → 12 mm loose jacket
-# (not yet plumbed — strict-raise), G/H → 25 mm foam, I-M → 38 mm foam.
-_TABLE_29_DEFAULT_CYLINDER_INSULATION_MM_BY_AGE: Final[dict[str, int]] = {
-    "G": 25, "H": 25, "I": 38, "J": 38, "K": 38, "L": 38, "M": 38,
+# accessible" — the §10.7 default cylinder uses the age-band insulation:
+# "Age band of main property A to F: 12 mm loose jacket", G/H → 25 mm
+# foam, I-M → 38 mm foam. Each entry is (cylinder_insulation_type,
+# thickness_mm); the loose-jacket branch is now plumbed (S0380.224) so
+# A-F resolves instead of raising.
+_TABLE_29_DEFAULT_CYLINDER_INSULATION_BY_AGE: Final[dict[str, tuple[int, int]]] = {
+    "A": (_CYLINDER_INSULATION_TYPE_LOOSE_JACKET, 12),
+    "B": (_CYLINDER_INSULATION_TYPE_LOOSE_JACKET, 12),
+    "C": (_CYLINDER_INSULATION_TYPE_LOOSE_JACKET, 12),
+    "D": (_CYLINDER_INSULATION_TYPE_LOOSE_JACKET, 12),
+    "E": (_CYLINDER_INSULATION_TYPE_LOOSE_JACKET, 12),
+    "F": (_CYLINDER_INSULATION_TYPE_LOOSE_JACKET, 12),
+    "G": (_CYLINDER_INSULATION_TYPE_FACTORY, 25),
+    "H": (_CYLINDER_INSULATION_TYPE_FACTORY, 25),
+    "I": (_CYLINDER_INSULATION_TYPE_FACTORY, 38),
+    "J": (_CYLINDER_INSULATION_TYPE_FACTORY, 38),
+    "K": (_CYLINDER_INSULATION_TYPE_FACTORY, 38),
+    "L": (_CYLINDER_INSULATION_TYPE_FACTORY, 38),
+    "M": (_CYLINDER_INSULATION_TYPE_FACTORY, 38),
 }
 
 
@@ -4487,9 +4806,8 @@ def _apply_rdsap_no_water_heating_system_default(
     Elmhurst engine's worksheet header for the corpus "no system" cert
     (WHS 903, Single immersion, 110 L cylinder, 25 mm foam at age G).
 
-    Raises `UnmappedSapCode` for age bands A-F (12 mm loose jacket) —
-    no corpus member exercises that combination and the SAP 10.2 Table 2
-    loss-factor dispatch only has the factory-foam path plumbed.
+    Raises `UnmappedSapCode` only when the main dwelling's age band is
+    absent / outside A-M (no Table 29 row to apply).
     """
     if epc.sap_heating.water_heating_code != _WHC_NO_WATER_HEATING_SYSTEM:
         return epc
@@ -4498,17 +4816,18 @@ def _apply_rdsap_no_water_heating_system_default(
         if epc.sap_building_parts else None
     )
     band = (age_band or "")[:1].upper()
-    thickness_mm = _TABLE_29_DEFAULT_CYLINDER_INSULATION_MM_BY_AGE.get(band)
-    if thickness_mm is None:
+    default = _TABLE_29_DEFAULT_CYLINDER_INSULATION_BY_AGE.get(band)
+    if default is None:
         raise UnmappedSapCode(
             "rdsap_10_7_default_cylinder_insulation_age_band", age_band
         )
+    insulation_type_code, thickness_mm = default
     sap_heating = replace(
         epc.sap_heating,
         water_heating_code=_WHC_ELECTRIC_IMMERSION,
         water_heating_fuel=_STANDARD_ELECTRICITY_FUEL_CODE,
         cylinder_size=_CYLINDER_SIZE_CODE_NORMAL_110L,
-        cylinder_insulation_type=_CYLINDER_INSULATION_TYPE_FACTORY,
+        cylinder_insulation_type=insulation_type_code,
         cylinder_insulation_thickness_mm=thickness_mm,
         cylinder_thermostat="Y",
     )
@@ -4594,6 +4913,20 @@ def _separately_timed_dhw(
         return False
     if main.sap_main_heating_code in _TABLE_4A_SOLID_FUEL_BOILER_CODES:
         return False
+    # SAP 10.2 Table 2b note b + RdSAP 10 §10.5.1 (PDF p.55): the ×0.9
+    # reduction reflects DHW timed separately from space heating on a
+    # SHARED heat generator. When DHW is from a separate dedicated
+    # water-heating-only system (water-heating code not "from main /
+    # 2nd-main system" — e.g. 911 "Gas boiler/circulator for water
+    # heating only") there is no shared timer to apply the ×0.9 against,
+    # so the multiplier must not fire — the same principle as the WHC
+    # 903 electric-immersion carve-out above. Simulated case 19 (electric
+    # storage main + WHS 911 + 210 L loose-jacket cylinder) is the
+    # worksheet case: (53) Temperature factor 0.6000 (not 0.54) and
+    # (59)m primary loss h=5 (Jan 64.5792, not 43.31) both confirm the
+    # DHW is not separately timed.
+    if epc.sap_heating.water_heating_code not in _WATER_INHERIT_FROM_MAIN_CODES:
+        return False
     return bool(epc.has_hot_water_cylinder)
 
 
@@ -4897,6 +5230,18 @@ def _primary_loss_applies(
     # kWh/yr primary loss to a system with no primary circuit at all.
     if water_heating_code == _WHC_ELECTRIC_IMMERSION:
         return False
+    # SAP 10.2 Table 3 (PDF p.160) row 1 — a dedicated "boiler/circulator
+    # for water heating only" (WHC 911 gas / 912 liquid / 913 solid /
+    # 921-931 range cooker with boiler) is a heat generator feeding the
+    # cylinder through a primary loop, so the loss applies regardless of
+    # the space-heating main. Checked off `water_heating_code` (not
+    # `main`) because for these certs the resolved DHW `main` is the
+    # SPACE main (e.g. an electric storage heater, SAP code 402) — the
+    # gas/oil water boiler isn't a `main_heating_detail`. Simulated case
+    # 19 (storage main + WHS 911 + 210 L cylinder): worksheet (59) = 676.68
+    # kWh/yr — zero before this branch.
+    if water_heating_code in _WATER_HEATING_BOILER_CIRCULATOR_CODES:
+        return True
     if main.main_heating_category == 4:
         if hp_record is None:
             # No PCDB record → assume separate-vessel (conservative; the
@@ -5421,14 +5766,17 @@ def _cylinder_storage_loss_override(
     volume_l = _CYLINDER_SIZE_CODE_TO_LITRES.get(size_code)
     if volume_l is None:
         return None
-    if sh.cylinder_insulation_type != _CYLINDER_INSULATION_TYPE_FACTORY:
+    insulation_label = _cylinder_storage_loss_insulation_label(
+        sh.cylinder_insulation_type
+    )
+    if insulation_label is None:
         return None
     thickness_mm = sh.cylinder_insulation_thickness_mm
     if thickness_mm is None:
         return None
     storage_56m = cylinder_storage_loss_monthly_kwh(
         volume_l=volume_l,
-        insulation_type="factory_insulated",
+        insulation_type=insulation_label,
         thickness_mm=float(thickness_mm),
         has_cylinder_thermostat=sh.cylinder_thermostat == "Y",
         # SAP 10.2 Table 2b note b (PDF p.159) verbatim restricts the
@@ -5785,10 +6133,15 @@ def _fuel_cost(
         table_32_unit_price_p_per_kwh(60) * _PENCE_TO_GBP
     )
 
-    standing = additional_standing_charges_gbp(
-        main_fuel_code=main_fuel_code,
-        water_heating_fuel_code=water_heating_fuel_code,
-        tariff=tariff,
+    heat_network_standing = _heat_network_standing_charge_gbp(epc, main)
+    standing = (
+        heat_network_standing
+        if heat_network_standing is not None
+        else additional_standing_charges_gbp(
+            main_fuel_code=main_fuel_code,
+            water_heating_fuel_code=water_heating_fuel_code,
+            tariff=tariff,
+        )
     )
 
     # Worksheet display convention: when a row's kWh is zero (no main 2, no
@@ -5833,9 +6186,7 @@ def _fuel_cost(
         pv_dwelling_kwh_per_yr=pv_dwelling_kwh_per_yr,
         pv_exported_kwh_per_yr=pv_exported_kwh_per_yr,
         pv_dwelling_import_price_gbp_per_kwh=(
-            _pv_dwelling_import_price_gbp_per_kwh(
-                epc.sap_energy_source.meter_type, prices
-            )
+            _pv_dwelling_import_price_gbp_per_kwh(_rdsap_tariff(epc), prices)
         ),
     )
 
@@ -5887,6 +6238,27 @@ def cert_to_inputs(
             has_balanced_mv=_has_balanced_mechanical_ventilation(epc),
         )
     )
+    # SAP 10.2 Table 4f note c) (PDF p.175): "Where there are two main
+    # heating systems include two figures from this table." A genuine
+    # second SPACE-heating main therefore contributes its own circulation
+    # pump alongside Main 1's. The "second main heating system" test is the
+    # same one §9a uses to split space-heating demand: a lodged
+    # `main_heating_fraction > 0`. This excludes DHW-only second mains
+    # (e.g. cert 000565 Main 2 = gas combi via WHC 914, fraction 0 — water
+    # heating only, no space-heating circulation pump). Simulated case 6
+    # (dual oil boiler, 51% rads + 49% underfloor) lodges Main 1 "2013 or
+    # later" (41 kWh) + Main 2 unknown-date (115 kWh) → worksheet (230c)
+    # central-heating pump = 41 + 115 = 156. The Main 2 oil-boiler aux
+    # (230d) is already summed in `_table_4f_additive_components`; this
+    # adds only the circulation pump.
+    _pumps_main_details = (
+        epc.sap_heating.main_heating_details if epc.sap_heating else []
+    )
+    if len(_pumps_main_details) >= 2:
+        _pumps_main_2 = _pumps_main_details[1]
+        _pumps_main_2_fraction = _pumps_main_2.main_heating_fraction
+        if _pumps_main_2_fraction is not None and _pumps_main_2_fraction > 0:
+            pumps_fans_kwh += _table_4f_circulation_pump_kwh(_pumps_main_2)
     pumps_fans_kwh += _table_4f_additive_components(epc)
     # Track the MEV/MVHR-fan portion separately so the cost cascade can
     # apply Table 12a Grid 2 `FANS_FOR_MECH_VENT` (0.58 high-frac on
@@ -6192,12 +6564,33 @@ def cert_to_inputs(
     # = transmission HLC + 0.33·V·(25)m. Table 4e control adjustment is 0
     # for the Elmhurst corpus (cert-side mapping is a future slice).
     control_type_value = _control_type(main)
-    responsiveness_value = _responsiveness(
-        main, tariff=tariff_from_meter_type(epc.sap_energy_source.meter_type),
-    )
+    _mit_tariff = tariff_from_meter_type(epc.sap_energy_source.meter_type)
+    responsiveness_value = _responsiveness(main, tariff=_mit_tariff)
     living_area_fraction_value = _living_area_fraction(
         epc.habitable_rooms_count, dim.total_floor_area_m2
     )
+    # SAP 10.2 Table 9b weighted R + p.186 two-systems-different-parts MIT.
+    # A genuine second main (main_heating_fraction > 0 = (203)) contributes
+    # its own responsiveness (Table 9b weighted average) and, when it
+    # carries a different control type, its own rest-of-dwelling control
+    # schedule. `_first_main_heating` is system 1 (living area); the second
+    # detail is system 2. Single-main / DHW-only second mains (frac 0) pass
+    # the None/0 defaults → unchanged single-system MIT.
+    _mit_details = epc.sap_heating.main_heating_details if epc.sap_heating else []
+    _mit_main_2 = _mit_details[1] if len(_mit_details) >= 2 else None
+    main_2_control_type_value: Optional[int] = None
+    main_2_fraction_value = 0.0
+    main_2_responsiveness_value = 1.0
+    if (
+        _mit_main_2 is not None
+        and _mit_main_2.main_heating_fraction is not None
+        and _mit_main_2.main_heating_fraction > 0
+    ):
+        main_2_control_type_value = _control_type(_mit_main_2)
+        main_2_fraction_value = _mit_main_2.main_heating_fraction / 100.0
+        main_2_responsiveness_value = _responsiveness(
+            _mit_main_2, tariff=_mit_tariff
+        )
     monthly_total_gains_w = tuple(
         internal_gains_monthly_w[m] + solar_gains_monthly_w[m] for m in range(12)
     )
@@ -6223,6 +6616,9 @@ def cert_to_inputs(
         responsiveness=responsiveness_value,
         living_area_fraction=living_area_fraction_value,
         control_temperature_adjustment_c=_control_temperature_adjustment_c(main),
+        main_2_control_type=main_2_control_type_value,
+        main_2_fraction=main_2_fraction_value,
+        main_2_responsiveness=main_2_responsiveness_value,
         extended_heating_days_per_month=extended_heating_days,
     )
 
@@ -6246,9 +6642,16 @@ def cert_to_inputs(
     # the scalar `water_eff` (Table 4a/4b boilers, legacy fallback).
     # Q_space (kWh/month) per spec = (98c)m × (204) = (98c)m × (1 −
     # sec_frac) for single-main fixtures.
+    space_heating_monthly_useful_kwh: tuple[float, ...] = (0.0,) * 12
     if wh_result is not None:
+        # Eq D1 Q_space is the DHW boiler's OWN space-heating load — its
+        # (204)/(205) share of total — not the dwelling total (202). See
+        # `_water_heating_main_space_fraction`.
+        water_main_space_fraction = _water_heating_main_space_fraction(
+            epc, secondary_fraction_value
+        )
         space_heating_monthly_useful_kwh = tuple(
-            q * (1.0 - secondary_fraction_value)
+            q * water_main_space_fraction
             for q in space_heating_result.total_space_heating_monthly_kwh
         )
         hw_kwh = _apply_water_efficiency(
@@ -6337,11 +6740,22 @@ def cert_to_inputs(
     secondary_efficiency_value = _secondary_efficiency(
         epc.sap_heating, main_code, main_fuel
     )
+    # SAP 10.2 §9a two-main split (203)/(207) — see the section helper
+    # `energy_requirements_section_from_cert` for the rationale.
+    _main_details = epc.sap_heating.main_heating_details if epc.sap_heating else []
+    _main_2 = _main_details[1] if len(_main_details) >= 2 else None
+    main_2_of_main_fraction = 0.0
+    main_2_efficiency_value = 0.0
+    if _main_2 is not None and _main_2.main_heating_fraction is not None:
+        main_2_of_main_fraction = _main_2.main_heating_fraction / 100.0
+        main_2_efficiency_value = _main_heating_detail_efficiency(_main_2, epc)
     energy_requirements_result = space_heating_fuel_monthly_kwh(
         space_heating_monthly_kwh=space_heating_result.total_space_heating_monthly_kwh,
         secondary_heating_fraction=secondary_fraction_value,
         main_heating_efficiency_pct=eff * 100.0,
         secondary_heating_efficiency_pct=secondary_efficiency_value * 100.0,
+        main_2_of_main_fraction=main_2_of_main_fraction,
+        main_2_efficiency_pct=main_2_efficiency_value * 100.0,
     )
 
     # SAP 10.2 Appendix M1 §3-4 (p.93-94): split monthly PV generation
@@ -6403,6 +6817,12 @@ def cert_to_inputs(
             )
             if epc.sap_heating.water_heating_fuel is not None else None
         ),
+        # SAP 10.2 Appendix M1 §3a — exclude the low-rate portion of an
+        # off-peak electric main from D_PV (the §10a high/low split that
+        # `_space_heating_fuel_cost_gbp_per_kwh` already bills).
+        main_space_high_rate_fraction=_main_space_heating_high_rate_fraction(
+            main, _rdsap_tariff(epc),
+        ),
     )
     pv_split = pv_split_monthly(
         epv_monthly_kwh=pv_monthly_kwh,
@@ -6410,17 +6830,70 @@ def cert_to_inputs(
         battery_capacity_kwh=_pv_battery_capacity_kwh(epc),
     )
 
+    # SAP 10.2 Appendix G4 (PDF p.72-73) — PV diverter. The β factor above
+    # is computed on the PRE-diverter (219) per the §3a note; now apply
+    # the diverter saving. SPV,diverter,m diverts the surplus PV (the
+    # would-be export EPV,m × (1 − βm)) into the cylinder immersion:
+    #   - (63b)m = −SPV,diverter,m reduces the §4 output (64)m → less main-
+    #     system water-heating fuel (219);
+    #   - the export drops to EPV,ex,m = EPV,m(1 − βm) + (63b)m / 0.9 (the
+    #     diverted energy is no longer exported); the onsite dwelling
+    #     portion EPV,dw,m = EPV,m × βm is unchanged (the β is fixed).
+    hw_output_monthly_for_factors = (
+        wh_result.output_monthly_kwh if wh_result is not None else (0.0,) * 12
+    )
+    pv_diverter_monthly_kwh = _pv_diverter_monthly_kwh(
+        epc=epc,
+        pv_export_monthly_kwh=pv_split.epv_exported_monthly_kwh,
+        water_demand_monthly_kwh=(
+            wh_result.total_demand_monthly_kwh if wh_result is not None
+            else (0.0,) * 12
+        ),
+        avg_daily_hot_water_l=(
+            wh_result.annual_avg_hot_water_l_per_day if wh_result is not None
+            else 0.0
+        ),
+        battery_capacity_kwh=_pv_battery_capacity_kwh(epc),
+        pv_generation_kwh=sum(pv_monthly_kwh),
+    )
+    if pv_diverter_monthly_kwh is not None and wh_result is not None:
+        pv63b_monthly_kwh = tuple(-s for s in pv_diverter_monthly_kwh)
+        # (64)m = (62)m + (63a)m + (63b)m — reduce the §4 output by the
+        # diverter input, then recompute (219) from the reduced output.
+        hw_output_monthly_for_factors = tuple(
+            max(0.0, wh_result.output_monthly_kwh[m] + pv63b_monthly_kwh[m])
+            for m in range(12)
+        )
+        if section_12_4_4_blend is None:
+            hw_kwh = _apply_water_efficiency(
+                wh_output_monthly_kwh=hw_output_monthly_for_factors,
+                wh_output_annual_kwh=sum(hw_output_monthly_for_factors),
+                water_efficiency_pct=water_eff,
+                eq_d1_winter_summer_pct=eq_d1_winter_summer_pct,
+                space_heating_monthly_useful_kwh=space_heating_monthly_useful_kwh,
+                interlock_penalty_pp=eq_d1_interlock_penalty_pp,
+            )
+        # EPV,ex,m = EPV,m(1 − βm) + (63b)m / fPV,diverter,storageloss.
+        adjusted_export_monthly_kwh = tuple(
+            pv_split.epv_exported_monthly_kwh[m]
+            + pv63b_monthly_kwh[m] / _PV_DIVERTER_STORAGE_LOSS_FACTOR
+            for m in range(12)
+        )
+        pv_split = PhotovoltaicSplit(
+            beta_monthly=pv_split.beta_monthly,
+            epv_dwelling_monthly_kwh=pv_split.epv_dwelling_monthly_kwh,
+            epv_exported_monthly_kwh=adjusted_export_monthly_kwh,
+        )
+
     # SAP 10.2 §12.4.4 overrides — when summer immersion applies (back-
     # boiler combo + cylinder + WHC from main heating), the HW cost /
     # CO2 / PE factors are kWh-weighted blends of the winter boiler fuel
     # + summer electric immersion. The standing-charges line adds the
     # off-peak electric standing because the cylinder is heated by an
     # off-peak immersion Jun-Sep. When the rule does NOT apply, the
-    # locals fall back to the existing single-fuel HW helpers.
-    hw_monthly_kwh_for_factors = (
-        wh_result.output_monthly_kwh if wh_result is not None
-        else (0.0,) * 12
-    )
+    # locals fall back to the existing single-fuel HW helpers. The HW
+    # factors weight by the diverter-adjusted (64)m output.
+    hw_monthly_kwh_for_factors = hw_output_monthly_for_factors
     if section_12_4_4_blend is not None:
         (
             _hw_total_unused,
@@ -6448,10 +6921,15 @@ def cert_to_inputs(
             epc, hw_monthly_kwh_for_factors, _rdsap_tariff(epc),
         )
         _hw_extra_standing = 0.0
-    standing_charges_total = additional_standing_charges_gbp(
-        main_fuel_code=_main_fuel_code(main),
-        water_heating_fuel_code=_water_heating_fuel_code(epc),
-        tariff=_rdsap_tariff(epc),
+    _heat_network_standing = _heat_network_standing_charge_gbp(epc, main)
+    standing_charges_total = (
+        _heat_network_standing
+        if _heat_network_standing is not None
+        else additional_standing_charges_gbp(
+            main_fuel_code=_main_fuel_code(main),
+            water_heating_fuel_code=_water_heating_fuel_code(epc),
+            tariff=_rdsap_tariff(epc),
+        )
     ) + _hw_extra_standing
 
     # SAP 10.2 Appendix C §C3.2 (PDF p.51) — heat-network distribution
@@ -6599,7 +7077,7 @@ def cert_to_inputs(
         pv_generation_kwh_per_yr=_pv_generation_kwh_per_yr(epc, climate),
         pv_export_credit_gbp_per_kwh=_pv_export_credit_gbp_per_kwh(),
         pv_dwelling_import_price_gbp_per_kwh=_pv_dwelling_import_price_gbp_per_kwh(
-            epc.sap_energy_source.meter_type, prices
+            _rdsap_tariff(epc), prices
         ),
         # SAP 10.2 Appendix M1 §3-4 PV split — the cascade applies
         # IMPORT PEF (Table 12) to the onsite portion and EXPORT PEF

domain/sap10_calculator/tables/table_12a.py

@@ -250,13 +250,16 @@ _RULE_2_STORAGE_CODES: Final[frozenset[int]] = frozenset(
 # Rule 3: direct-acting electric + heat pumps + electric room heaters
 # → 10-hour. §12 lists "heat pump (211 to 224, 521 to 524, or
 # database)" — the "database" branch fires when the cert lodges a
-# PCDB Table 362 heat-pump index regardless of SAP code.
+# PCDB Table 362 heat-pump index regardless of SAP code. §12 also
+# names "electric room heaters" verbatim (RdSAP 10 PDF p.62) — Table 4a
+# electric room-heater codes 691 (panel/convector/radiant), 692 (fan),
+# 693 (portable), 694 (water-/oil-filled), 699 (assumed). Without these
+# a Dual-meter room-heater cert fell through to Rule 4 (7-hour default).
 _RULE_3_TEN_HOUR_CODES: Final[frozenset[int]] = frozenset(
     [191]                       # direct-acting electric boiler
     + list(range(211, 225))     # heat pumps 211-224
     + list(range(521, 525))     # warm-air heat pumps 521-524
-    # TODO: electric room heater codes (SAP Table 4a row 6xx for
-    # electric panel / radiant heaters) when a fixture surfaces them.
+    + [691, 692, 693, 694, 699]  # electric room heaters (Table 4a)
 )
 
 

domain/sap10_calculator/worksheet/energy_requirements.py

@@ -11,8 +11,10 @@ where (204) = (202) × (1 − (203)) and (202) = 1 − (201). Single-main
 case ((203) = 0) collapses (204) to (202), so (211)m = (98c)m × (202) ×
 100 / (206). Same shape for secondary (215)m and main 2 (213)m.
 
-Two-main split ((203) > 0) and cooling-fuel (209)/(221) are zero-branch
-placeholders in scope A — populated once first cert exercises them.
+Two-main split ((203) > 0) is implemented: (211)m = (98c)m × (204) ×
+100 / (206) for system 1 and (213)m = (98c)m × (205) × 100 / (207) for
+system 2, where (204) = (202) × (1 − (203)) and (205) = (202) × (203).
+Cooling-fuel (209)/(221) remains a zero-branch placeholder.
 
 Reference: SAP 10.2 specification (14-03-2025) §9a (lines 7909-7953).
 """
@@ -26,10 +28,9 @@ from dataclasses import dataclass
 class EnergyRequirementsResult:
     """SAP 10.2 §9a worksheet line refs (201)..(221).
 
-    Scope-A populated lines: (201), (202), (204), (206), (208), (211)m,
-    (211), (215)m, (215). Two-main and cooling-fuel line refs ((203),
-    (205), (207), (209), (213)m, (213), (221)) are zero-branch
-    placeholders until the first multi-main / fixed-AC cert lands.
+    Populated lines: (201)-(208), (211)m/(211), (213)m/(213) (two-main
+    split), (215)m/(215). Cooling-fuel line refs ((209), (221)) are
+    zero-branch placeholders until the first fixed-AC cert lands.
     """
 
     # Fractions (Table 11)
@@ -60,26 +61,37 @@ def space_heating_fuel_monthly_kwh(
     secondary_heating_fraction: float,
     main_heating_efficiency_pct: float,
     secondary_heating_efficiency_pct: float,
+    main_2_of_main_fraction: float = 0.0,
+    main_2_efficiency_pct: float = 0.0,
 ) -> EnergyRequirementsResult:
     """SAP 10.2 §9a orchestrator — produce (201)..(221) line refs.
 
-    Scope A: single-main + secondary only. Two-main ((203) > 0) and
-    cooling-fuel (Table 10c SEER) populate the zero-branch placeholder
-    fields with computed values when their respective slices land.
+    Single-main certs leave `main_2_of_main_fraction` = 0, collapsing
+    (204) to (202) and zeroing (213)m. Dual-main certs (cert 0240 /
+    simulated case 6) pass (203) = fraction of main heating from main
+    system 2 and (207) = main system 2 efficiency; the §8 space-heat
+    demand then splits (204)=(202)×(1−(203)) to system 1 and
+    (205)=(202)×(203) to system 2, each at its own efficiency. Cooling-
+    fuel (Table 10c SEER) remains a zero-branch placeholder.
     """
     fraction_201 = secondary_heating_fraction
     fraction_202 = 1.0 - fraction_201
-    fraction_203 = 0.0  # scope A: no main 2
+    fraction_203 = main_2_of_main_fraction
     fraction_204 = fraction_202 * (1.0 - fraction_203)
     fraction_205 = fraction_202 * fraction_203
 
     main_1_eff = main_heating_efficiency_pct
+    main_2_eff = main_2_efficiency_pct
     secondary_eff = secondary_heating_efficiency_pct
 
     main_1_fuel_monthly = tuple(
         q * fraction_204 * 100.0 / main_1_eff if main_1_eff > 0 else 0.0
         for q in space_heating_monthly_kwh
     )
+    main_2_fuel_monthly = tuple(
+        q * fraction_205 * 100.0 / main_2_eff if main_2_eff > 0 else 0.0
+        for q in space_heating_monthly_kwh
+    )
     secondary_fuel_monthly = tuple(
         q * fraction_201 * 100.0 / secondary_eff if secondary_eff > 0 else 0.0
         for q in space_heating_monthly_kwh
@@ -92,14 +104,14 @@ def space_heating_fuel_monthly_kwh(
         main_1_of_total_fraction=fraction_204,
         main_2_of_total_fraction=fraction_205,
         main_1_efficiency_pct=main_1_eff,
-        main_2_efficiency_pct=0.0,
+        main_2_efficiency_pct=main_2_eff,
         secondary_efficiency_pct=secondary_eff,
         cooling_seer=0.0,
         main_1_fuel_monthly_kwh=main_1_fuel_monthly,
-        main_2_fuel_monthly_kwh=(0.0,) * 12,
+        main_2_fuel_monthly_kwh=main_2_fuel_monthly,
         secondary_fuel_monthly_kwh=secondary_fuel_monthly,
         main_1_fuel_kwh_per_yr=sum(main_1_fuel_monthly),
-        main_2_fuel_kwh_per_yr=0.0,
+        main_2_fuel_kwh_per_yr=sum(main_2_fuel_monthly),
         secondary_fuel_kwh_per_yr=sum(secondary_fuel_monthly),
         cooling_fuel_kwh_per_yr=0.0,
     )

domain/sap10_calculator/worksheet/heat_transmission.py

@@ -300,6 +300,36 @@ def _parse_thickness_mm(value: Any) -> Optional[int]:
     return int(digits) if digits else None
 
 
+def _described_as_retrofit_insulated(description: Optional[str]) -> bool:
+    """True only when the description asserts insulation KNOWN to have
+    been added subsequently — i.e. genuine retrofit, not the age-band
+    as-built assumption.
+
+    RdSAP 10 Table 8/9 footnote routes a wall to the 50 mm "insulation
+    of unknown thickness" row ONLY when insulation is "known to have been
+    increased subsequently (otherwise 'as built' applies)". A description
+    rendered as "as built ... insulated (assumed)" is the EPC's age-band
+    assumption — it renders only on recent age bands where as-built
+    construction already includes insulation (an old band renders "no
+    insulation (assumed)"). For those the spec uses the as-built age-band
+    U-value, NOT the 50 mm retrofit row.
+
+    Worksheet evidence: simulated case 9 (sandstone, band J, As Built →
+    U 0.35) and case 10 (solid brick, band J, As Built → U 0.35); both
+    Elmhurst worksheets return the as-built row, not the 50 mm bucket
+    (which gives ~0.25). Genuine retrofit is signalled by
+    `wall_insulation_type` (External/Internal/Filled), checked
+    independently by the `wall_ins_present` gate — so excluding the
+    "as built"/"(assumed)" description here loses no real retrofit signal.
+    """
+    if description is None:
+        return False
+    if not _described_as_insulated(description):
+        return False
+    desc = description.lower()
+    return "as built" not in desc and "assumed" not in desc
+
+
 def _joined_descriptions(elements: list[Any]) -> Optional[str]:
     if not elements:
         return None
@@ -311,6 +341,13 @@ def _joined_descriptions(elements: list[Any]) -> Optional[str]:
 
 def _part_geometry(part: SapBuildingPart) -> dict[str, float]:
     if not part.sap_floor_dimensions:
+        # A part with no floor dimensions has no derivable RR shell or
+        # cantilever geometry, but the early return must still expose the
+        # SAME keys as the full return below: the §3.9 RR block reads
+        # geom["rr_common_wall_area_m2"] / ["rr_gable_area_m2"] /
+        # ["cantilever_floor_area_m2"] for every part, so omitting them
+        # here raised KeyError on multi-part certs whose first bp lodges
+        # no sap_floor_dimensions (5 certs in a 2026 API sample).
         return {
             "ground_floor_area_m2": 0.0,
             "top_floor_area_m2": 0.0,
@@ -318,6 +355,9 @@ def _part_geometry(part: SapBuildingPart) -> dict[str, float]:
             "party_wall_area_m2": 0.0,
             "rr_floor_area_m2": 0.0,
             "rr_simplified_a_rr_m2": 0.0,
+            "rr_common_wall_area_m2": 0.0,
+            "rr_gable_area_m2": 0.0,
+            "cantilever_floor_area_m2": 0.0,
         }
     fds = list(part.sap_floor_dimensions)
     ground = next((fd for fd in fds if fd.floor == 0), fds[0])
@@ -450,6 +490,45 @@ def _part_geometry(part: SapBuildingPart) -> dict[str, float]:
     }
 
 
+_RR_ROOF_LODGEMENT_KINDS: Final[frozenset[str]] = frozenset(
+    {"slope", "flat_ceiling", "stud_wall"}
+)
+
+
+def _bp_rr_roof_absorbs_rooflight(
+    part: SapBuildingPart, geom: dict[str, Any]
+) -> bool:
+    """Whether a rooflight on this building part pierces the room-in-roof
+    sloped ceiling (so it deducts from the RR roof contribution) rather
+    than a flat external roof.
+
+    True ONLY for a Detailed RR (§3.10) lodging wall surfaces but no roof
+    surfaces (gable / common / connected, no slope / flat_ceiling /
+    stud_wall): the §3.10.1 residual roof fires and the rooflight deducts
+    from it (simulated case 6: the 6 "Roof of Room" rooflights deduct from
+    "Roof room Main remaining" net 55.54 = gross 61.73 − 6.19).
+
+    False otherwise:
+      - Simplified Type 1/2 RR (geom A_RR > 0, certs 6035 / 0240): the
+        rooflight pierces the regular loft roof at U_roof, NOT the A_RR
+        shell — its area deducts from `roof_area` (the test
+        `test_6035_api_room_in_roof_gables_deduct_from_roof` pins this).
+      - Detailed RR lodging explicit roof surfaces (cert 000565 Ext2 stud
+        walls / 000516 slopes): the rooflight pierces the regular roof.
+    Both keep the pre-S0380.203 §3.7 "deduct from the host roof" behaviour.
+    """
+    if geom["rr_simplified_a_rr_m2"] > 0:
+        return False
+    rir = part.sap_room_in_roof
+    if rir is None or not rir.detailed_surfaces:
+        return False
+    if float(rir.floor_area) <= 0.0:
+        return False
+    return not any(
+        s.kind in _RR_ROOF_LODGEMENT_KINDS for s in rir.detailed_surfaces
+    )
+
+
 def heat_transmission_from_cert(
     epc: EpcPropertyData,
     *,
@@ -626,14 +705,21 @@ def heat_transmission_from_cert(
         wall_construction = _int_or_none(part.wall_construction)
         wall_ins_type = _int_or_none(part.wall_insulation_type)
         wall_ins_thickness = _parse_thickness_mm(part.wall_insulation_thickness)
-        # Per RdSAP 10 Table 6 footnote, a wall with "insulated (assumed)"
-        # or "partial insulation (assumed)" in its description has retrofit
-        # insulation the assessor hasn't measured the thickness of — even
-        # when wall_insulation_type=4 ("as-built / assumed"). Treat as
-        # present so the 50 mm bucket routes correctly.
+        # RdSAP 10 Table 8/9 footnote: the 50 mm "insulation of unknown
+        # thickness" row applies only when insulation is "known to have
+        # been increased subsequently (otherwise 'as built' applies)".
+        # Genuine retrofit is signalled by `wall_insulation_type`
+        # (External/Internal/Filled ≠ NONE). An "as built ... insulated
+        # (assumed)" description is the EPC age-band assumption (it only
+        # renders on recent bands where as-built already includes
+        # insulation) → use the as-built age-band row, NOT 50 mm.
+        # Worksheet-validated by simulated case 9 (sandstone J → 0.35)
+        # and case 10 (solid brick J → 0.35), both As Built. So the
+        # description signal is restricted to genuine (non-assumed)
+        # retrofit via `_described_as_retrofit_insulated`.
         wall_ins_present = (
             (wall_ins_type is not None and wall_ins_type != _WALL_INSULATION_NONE)
-            or _described_as_insulated(wall_description)
+            or _described_as_retrofit_insulated(wall_description)
         )
         party_construction = _int_or_none(part.party_wall_construction)
         raw_roof_thickness = getattr(part, "roof_insulation_thickness", None)
@@ -674,6 +760,10 @@ def heat_transmission_from_cert(
                 # insulation_type combination doesn't match the formula
                 # path's preconditions.
                 wall_thickness_mm=part.wall_thickness_mm,
+                # RdSAP 10 §5.8 — lodged insulation thermal-conductivity
+                # code feeds the documentary-evidence R-value calc when a
+                # measured wall thickness is also present (else ignored).
+                wall_insulation_thermal_conductivity=part.wall_insulation_thermal_conductivity,
             )
         # When the per-bp `roof_insulation_thickness` is explicitly lodged
         # as 0 (uninsulated — e.g. cert 001479 Ext2 PS sloping ceiling
@@ -707,7 +797,21 @@ def heat_transmission_from_cert(
         # spec value is 2.30 (A-D) / 1.50 (E) / 0.68 (F) / 0.40 (G).
         roof_type_lower = (part.roof_construction_type or "").lower()
         is_flat_roof = "flat" in roof_type_lower
-        ur = u_roof(country=country, age_band=age_band, insulation_thickness_mm=roof_thickness, description=effective_roof_description, is_flat_roof=is_flat_roof)
+        # RdSAP 10 §5.11 Table 18 — a pitched roof whose ceiling follows the
+        # slope ("Pitched, sloping ceiling" code 8 / "Pitched (vaulted
+        # ceiling)" code 5) has no loft void, so an unknown-thickness
+        # lodgement takes the column (3) "Flat roof / sloping ceiling"
+        # age-band default rather than the §5.11.4 retrofit-50 mm joist row.
+        is_sloping_ceiling = (
+            "sloping ceiling" in roof_type_lower or "vaulted" in roof_type_lower
+        )
+        # RdSAP 10 Table 18 col (3) routing for an AS-BUILT "Pitched,
+        # sloping ceiling" (code 8). Narrower than `is_sloping_ceiling`
+        # (which also covers code-5 vaulted): vaulted ceilings stay on
+        # col (1) per the cohort, so only the literal "sloping ceiling"
+        # string triggers the col (3) age-band default in `u_roof`.
+        is_pitched_sloping_ceiling = "sloping ceiling" in roof_type_lower
+        ur = u_roof(country=country, age_band=age_band, insulation_thickness_mm=roof_thickness, description=effective_roof_description, is_flat_roof=is_flat_roof, is_sloping_ceiling=is_sloping_ceiling, is_pitched_sloping_ceiling=is_pitched_sloping_ceiling)
         # Floor U-value routing (in priority order):
         #   1. Basement floor — Table 23 F-column override (whole floor=0).
         #   2. Exposed/semi-exposed upper floor — Table 20 lookup; no
@@ -811,7 +915,23 @@ def heat_transmission_from_cert(
         if "sloping ceiling" in roof_type:
             top_floor_area = top_floor_area / _COS_30_DEG
         gross_roof_area = _round_half_up(top_floor_area, _AREA_ROUND_DP)
-        roof_area = max(0.0, gross_roof_area - rw_area_part)
+        # RdSAP 10 §3.7 — a rooflight deducts from the gross roof of the
+        # element it physically pierces. A "Roof of Room" rooflight sits on
+        # the room-in-roof sloped ceiling (the §3.9/§3.10 A_RR shell), not a
+        # flat external roof, so its area deducts from the RR roof
+        # contribution (simplified A_RR_final or the §3.10.1 detailed
+        # residual) rather than `roof_area` — but ONLY when the BP's RR
+        # actually contributes such a shell/residual. Where the BP lodges
+        # explicit roof surfaces (cert 000565 Ext2 stud walls / 000516
+        # slopes), the rooflight pierces those (the regular roof) and
+        # deducts there per §3.7 (current behaviour). Simulated case 6
+        # worksheet: "Roof room Main remaining area" net 55.54 = gross 61.73
+        # − 6.19 rooflights, while "External roof Main" 14.52 carries no
+        # opening.
+        rw_area_on_rr = (
+            rw_area_part if _bp_rr_roof_absorbs_rooflight(part, geom) else 0.0
+        )
+        roof_area = max(0.0, gross_roof_area - (rw_area_part - rw_area_on_rr))
         floor_area_total = _round_half_up(
             geom["ground_floor_area_m2"] if exposure.has_exposed_floor else 0.0,
             _AREA_ROUND_DP,
@@ -860,19 +980,28 @@ def heat_transmission_from_cert(
         # U_main_wall per spec page 23 ("Common wall U-value is inferred
         # from the U-value of the main wall in the building part below";
         # gables fall under the same Table 4 rule).
-        rr_a_rr = geom["rr_simplified_a_rr_m2"]
-        rr_common = geom["rr_common_wall_area_m2"]
-        rr_gable = geom["rr_gable_area_m2"]
+        # `rr_roof_area` is the worksheet's simplified A_RR (the notional
+        # room-in-roof roof area, RdSAP 10 §3.10.1). Its perimeter common
+        # walls + gables are billed to walls; the leftover residual is the
+        # roof-going area that takes the roof U-value.
+        rr_roof_area = geom["rr_simplified_a_rr_m2"]
+        rr_common_wall_area = geom["rr_common_wall_area_m2"]
+        rr_gable_area = geom["rr_gable_area_m2"]
         rr_detailed_area = 0.0
-        if rr_a_rr > 0:
+        if rr_roof_area > 0:
             rir = part.sap_room_in_roof
-            assert rir is not None  # rr_a_rr > 0 ⇒ rir present per _part_geometry
-            walls += uw * (rr_common + rr_gable)
-            a_rr_final = max(0.0, rr_a_rr - rr_common - rr_gable)
+            assert rir is not None  # rr_roof_area > 0 ⇒ rir present per _part_geometry
+            walls += uw * (rr_common_wall_area + rr_gable_area)
+            # Deduct any "Roof of Room" rooflights piercing the RR shell
+            # (see `rw_area_on_rr` rationale at the gross-roof block).
+            rr_residual_roof_area = max(
+                0.0,
+                rr_roof_area - rr_common_wall_area - rr_gable_area - rw_area_on_rr,
+            )
             u_rr = u_rr_default_all_elements(
                 country=country, age_band=rir.construction_age_band,
             )
-            roof += u_rr * a_rr_final
+            roof += u_rr * rr_residual_roof_area
         elif part.sap_room_in_roof is not None and part.sap_room_in_roof.detailed_surfaces:
             # RdSAP10 §3.10 Detailed RR — iterate per-surface lodgement.
             # Slope / flat_ceiling / stud_wall route to roof (worksheet
@@ -885,7 +1014,8 @@ def heat_transmission_from_cert(
             # band". Wall-going RIR surfaces (gable_wall, gable_wall_
             # external, common_wall) deduct from the simplified A_RR
             # to leave the residual area, mirroring the Simplified
-            # branch's `a_rr_final = rr_a_rr - rr_common - rr_gable`.
+            # branch's `rr_residual_roof_area = rr_roof_area -
+            # rr_common_wall_area - rr_gable_area`.
             # Roof-going surfaces (slope / flat_ceiling / stud_wall)
             # do NOT deduct — they sit inside the RR shell rather than
             # forming its perimeter walls.
@@ -1003,7 +1133,13 @@ def heat_transmission_from_cert(
                 a_rr_shell = _round_half_up(
                     12.5 * sqrt(rr_floor_for_a_rr / 1.5), _AREA_ROUND_DP,
                 )
-                residual_area = max(0.0, a_rr_shell - rr_walls_in_a_rr_area)
+                # Deduct any "Roof of Room" rooflights piercing the RR
+                # residual (see `rw_area_on_rr` rationale at the gross-roof
+                # block) — case 6: 93.09 shell − 31.36 gables − 6.19
+                # rooflights = 55.54 net = worksheet "Roof room remaining".
+                residual_area = max(
+                    0.0, a_rr_shell - rr_walls_in_a_rr_area - rw_area_on_rr
+                )
                 if residual_area > 0.0:
                     rr_detailed_area += residual_area
                     roof += residual_area * u_rr_default_all_elements(
@@ -1051,7 +1187,7 @@ def heat_transmission_from_cert(
             main_wall_area
             + (alt_walls_total_area - alt_window_area)
             + roof_area + floor_area_total
-            + w_area + d_area + rw_area_part + rr_a_rr + rr_detailed_area
+            + w_area + d_area + rw_area_part + rr_roof_area + rr_detailed_area
             + cantilever_area
         )
         total_external_area += part_external_area
@@ -1109,7 +1245,7 @@ def _alt_wall_w_per_k(
     alt_thickness = _parse_thickness_mm(alt_wall.wall_insulation_thickness)
     alt_insulation_present = (
         alt_wall.wall_insulation_type != _WALL_INSULATION_NONE
-        or _described_as_insulated(wall_description)
+        or _described_as_retrofit_insulated(wall_description)
     )
     alt_u = u_wall(
         country=country,

domain/sap10_calculator/worksheet/internal_gains.py

@@ -27,9 +27,13 @@ from dataclasses import dataclass
 from decimal import Decimal, ROUND_HALF_UP
 from enum import Enum
 from math import cos, exp, pi
-from typing import Final
+from typing import Final, Optional
 
-from datatypes.epc.domain.epc_property_data import EpcPropertyData, SapWindow
+from datatypes.epc.domain.epc_property_data import (
+    EpcPropertyData,
+    MainHeatingDetail,
+    SapWindow,
+)
 
 
 def _decimal_window_area_2dp(width: float, height: float) -> float:
@@ -634,15 +638,15 @@ def _daylight_factor_from_cert(
     return 52.2 * g_l * g_l - 9.94 * g_l + 1.433
 
 
-def _pump_date_category_from_cert(epc: EpcPropertyData) -> PumpDateCategory:
-    """Map first main-heating detail's central_heating_pump_age_str to a
+def _pump_date_category_for_detail(
+    detail: Optional[MainHeatingDetail],
+) -> PumpDateCategory:
+    """Map a `MainHeatingDetail`'s central_heating_pump_age_str to a
     Table 5a bucket. Elmhurst lodges "Pre 2013" / "Post 2013" / "Unknown"
-    / None on each `MainHeatingDetail` (nested under `epc.sap_heating`)."""
-    sap_heating = getattr(epc, "sap_heating", None)
-    details = getattr(sap_heating, "main_heating_details", None) or []
+    / None on each detail."""
     age_str = ""
-    if details:
-        age_str = (details[0].central_heating_pump_age_str or "").lower()
+    if detail is not None:
+        age_str = (detail.central_heating_pump_age_str or "").lower()
     if "post" in age_str or "2013 or later" in age_str:
         return PumpDateCategory.NEW_2013_OR_LATER
     if "pre" in age_str or "2012" in age_str:
@@ -650,6 +654,14 @@ def _pump_date_category_from_cert(epc: EpcPropertyData) -> PumpDateCategory:
     return PumpDateCategory.UNKNOWN
 
 
+def _pump_date_category_from_cert(epc: EpcPropertyData) -> PumpDateCategory:
+    """Table 5a date bucket for Main 1 (the dwelling's first circulation
+    pump). Delegates to `_pump_date_category_for_detail`."""
+    sap_heating = getattr(epc, "sap_heating", None)
+    details = getattr(sap_heating, "main_heating_details", None) or []
+    return _pump_date_category_for_detail(details[0] if details else None)
+
+
 # SAP 10.2 Table 5a Note a) (PDF p.177): "Not applicable for electric
 # heat pumps from database." The pump GAIN (worksheet line 70) is
 # omitted only for HP-category systems. Where the cert lodges a
@@ -730,33 +742,69 @@ def _any_main_system_has_central_heating_pump(epc: EpcPropertyData) -> bool:
     details = epc.sap_heating.main_heating_details
     if not details:
         return False
-    for d in details:
-        if d.main_heating_category == _HEAT_PUMP_MAIN_HEATING_CATEGORY:
-            # PCDB Table 362 record → pump electricity AND gain are
-            # embedded in COP (Appendix N1.2.1); no separate gain row.
-            if d.main_heating_index_number is not None:
-                continue
-            # Cat 5 warm-air HP (codes 521/523-527) → no water pump.
-            code = d.sap_main_heating_code
-            if code is not None and code in _TABLE_4A_WARM_AIR_SAP_CODES:
-                continue
-            # Cat 4 HP, Table 4a default cascade → apply Table 5a
-            # pump gain per Appendix N3.1.
-            return True
-        code = d.sap_main_heating_code
-        if code is not None and any(
-            code in r for r in _WET_BOILER_SAP_CODE_RANGES
-        ):
-            return True
+    return any(_main_detail_has_central_heating_pump(d) for d in details)
+
+
+def _main_detail_has_central_heating_pump(d: MainHeatingDetail) -> bool:
+    """Whether a single `MainHeatingDetail` carries a Table 5a central-
+    heating-pump gain — the per-detail core of
+    `_any_main_system_has_central_heating_pump` (see that docstring for
+    the wet-main identification + HP rules)."""
+    if d.main_heating_category == _HEAT_PUMP_MAIN_HEATING_CATEGORY:
+        # PCDB Table 362 record → pump electricity AND gain are
+        # embedded in COP (Appendix N1.2.1); no separate gain row.
         if d.main_heating_index_number is not None:
-            return True
-        if d.main_heating_category in {1, 2}:
-            return True
-        if d.heat_emitter_type in _WET_HEAT_EMITTER_TYPES:
-            return True
+            return False
+        # Cat 5 warm-air HP (codes 521/523-527) → no water pump.
+        code = d.sap_main_heating_code
+        if code is not None and code in _TABLE_4A_WARM_AIR_SAP_CODES:
+            return False
+        # Cat 4 HP, Table 4a default cascade → apply Table 5a
+        # pump gain per Appendix N3.1.
+        return True
+    code = d.sap_main_heating_code
+    if code is not None and any(code in r for r in _WET_BOILER_SAP_CODE_RANGES):
+        return True
+    if d.main_heating_index_number is not None:
+        return True
+    if d.main_heating_category in {1, 2}:
+        return True
+    if d.heat_emitter_type in _WET_HEAT_EMITTER_TYPES:
+        return True
     return False
 
 
+def _second_main_central_heating_pump_gain_w(epc: EpcPropertyData) -> float:
+    """SAP 10.2 Table 5a note a) (PDF p.177): "Where there are two main
+    heating systems serving different parts of the dwelling, assume each
+    has its own circulation pump and therefore include two figures from
+    this table. ... Where two main systems serve the same space a single
+    pump is assumed."
+
+    Returns the SECOND main system's central-heating-pump gain (W,
+    heating-season) when a genuine second SPACE-heating main is lodged —
+    detected by `main_heating_fraction > 0`, the same gate
+    `cert_to_inputs` uses to split §9a space-heating demand and to add
+    the Table 4f note c) second circulation pump (S0380.201). Excludes
+    DHW-only second mains (fraction 0, e.g. cert 000565 Main 2 combi via
+    WHC 914). The gain uses the SECOND main's own pump-age bucket — for
+    simulated case 6 (dual oil, Main 2 unknown date) that is 7 W, giving
+    worksheet (70) = 3 (Main 1) + 7 (Main 2) = 10.
+    """
+    details = epc.sap_heating.main_heating_details
+    if len(details) < 2:
+        return 0.0
+    second = details[1]
+    fraction = second.main_heating_fraction
+    if fraction is None or fraction <= 0:
+        return 0.0
+    if not _main_detail_has_central_heating_pump(second):
+        return 0.0
+    return central_heating_pump_w(
+        date_category=_pump_date_category_for_detail(second)
+    )
+
+
 # SAP 10.2 Table 4a (PDF p.165-166) warm-air heating SAP codes. The
 # Table 5a "Warm air heating system fans" gain (and Table 4f
 # electricity row) fire for these mains:
@@ -881,6 +929,11 @@ def internal_gains_from_cert(
         pump_w = central_heating_pump_w(
             date_category=_pump_date_category_from_cert(epc)
         )
+        # SAP 10.2 Table 5a note a) — a second main heating system serving
+        # a different part of the dwelling has its own circulation pump
+        # (two figures from the table). Simulated case 6 (dual oil, rads +
+        # underfloor) → Main 1 3 W + Main 2 7 W = worksheet (70) 10 W.
+        pump_w += _second_main_central_heating_pump_gain_w(epc)
     else:
         pump_w = 0.0
     # SAP 10.2 Table 5a row "Warm air heating system fans a) c)" (PDF

domain/sap10_calculator/worksheet/mean_internal_temperature.py

@@ -321,6 +321,9 @@ def mean_internal_temperature_monthly(
     control_temperature_adjustment_c: float = 0.0,
     secondary_fraction: float = 0.0,
     secondary_responsiveness: float = 1.0,
+    main_2_control_type: Optional[int] = None,
+    main_2_fraction: float = 0.0,
+    main_2_responsiveness: float = 1.0,
     extended_heating_days_per_month: Optional[tuple[tuple[int, int], ...]] = None,
 ) -> MeanInternalTemperatureResult:
     """SAP 10.2 §7 orchestrator — chain Table 9c steps 1–9 for all 12 months.
@@ -354,13 +357,36 @@ def mean_internal_temperature_monthly(
                           standard SAP heating schedule applies: T_zone
                           = T_bimodal directly.
     """
+    # SAP 10.2 Table 9b (PDF p.183) — "where there are two main systems R
+    # is a weighted average ... R = (203)·R_system2 + [1 − (203)]·R_system1".
+    # (203) = `main_2_fraction`. Applied before the secondary-heating blend.
+    main_responsiveness = responsiveness
+    if main_2_control_type is not None and main_2_fraction > 0.0:
+        main_responsiveness = (
+            (1.0 - main_2_fraction) * responsiveness
+            + main_2_fraction * main_2_responsiveness
+        )
     effective_responsiveness = (
-        (1.0 - secondary_fraction) * responsiveness
+        (1.0 - secondary_fraction) * main_responsiveness
         + secondary_fraction * secondary_responsiveness
     )
     elsewhere_off_hours = (
         _ELSEWHERE_OFF_HOURS_TYPE_3 if control_type == 3 else _ELSEWHERE_OFF_HOURS_TYPE_12
     )
+    # SAP 10.2 p.186 "two systems heat different parts of the house": when
+    # the two mains carry different controls, the rest-of-dwelling (90)m is
+    # the weighted average of T2 computed under EACH system's control. The
+    # elsewhere off-hours for main system 2's control:
+    two_main_different_parts = (
+        main_2_control_type is not None
+        and main_2_fraction > 0.0
+        and main_2_control_type != control_type
+    )
+    elsewhere_off_hours_main_2 = (
+        _ELSEWHERE_OFF_HOURS_TYPE_3
+        if main_2_control_type == 3
+        else _ELSEWHERE_OFF_HOURS_TYPE_12
+    )
 
     eta_living: list[float] = []
     t_1: list[float] = []
@@ -408,6 +434,34 @@ def mean_internal_temperature_monthly(
         )
         eta_elsewhere.append(eta_e)
 
+        # SAP 10.2 p.186 part 2 — two systems heat different parts: blend
+        # the rest-of-dwelling temperature computed under each system's
+        # control. Th2 + η are identical for control types 2/3 (Table 9
+        # uses the same Th2 formula); only the off-hours differ, so the
+        # second computation reuses t_h2_m and shares η. Weights:
+        #   sys2 control:  (203) / [1 − (91)]
+        #   sys1 control:  [1 − (203) − (91)] / [1 − (91)]
+        # If (203) ≥ rest-of-house area [1 − (91)], use sys2's control
+        # alone for elsewhere (per the spec's threshold clause).
+        if two_main_different_parts:
+            rest_of_house = 1.0 - living_area_fraction
+            _, t_e_main_2 = _zone_mean_temp_with_per_zone_eta(
+                heating_temperature_c=t_h2_m,
+                off_hours_first=elsewhere_off_hours_main_2[0],
+                off_hours_second=elsewhere_off_hours_main_2[1],
+                external_temp_c=ext, responsiveness=effective_responsiveness,
+                total_gains_w=gains, heat_transfer_coefficient_w_per_k=h,
+                time_constant_h=tau,
+            )
+            if rest_of_house <= 0.0 or main_2_fraction >= rest_of_house:
+                t_e_bimodal = t_e_main_2
+            else:
+                w_main_2 = main_2_fraction / rest_of_house
+                w_main_1 = (
+                    rest_of_house - main_2_fraction
+                ) / rest_of_house
+                t_e_bimodal = w_main_1 * t_e_bimodal + w_main_2 * t_e_main_2
+
         # SAP 10.2 Appendix N3.5 Equation N5 — when the caller provides
         # per-month (N24,9, N16,9) day allocations, blend Th / T_unimodal
         # / T_bimodal for each zone. T_unimodal applies one 8-hour off

domain/sap10_ml/rdsap_uvalues.py

@@ -52,14 +52,11 @@ def _described_as_insulated(description: Optional[str]) -> bool:
     otherwise. Looks for "insulated" or "partial insulation" substrings,
     with "no insulation" taking precedence as a hard negation.
 
-    Two consumers:
-    - `u_wall` uses this to route cavity walls to the Filled-cavity row
-      of Table 6 (in lieu of the bucketed cascade).
-    - `heat_transmission_from_cert` uses this to set `wall_ins_present`
-      for non-cavity walls so the 50 mm bucket routing fires per the
-      RdSAP 10 Table 6 footnote ("If a wall is known to have additional
-      insulation but the insulation thickness is unknown, use the row
-      in the table for 50 mm insulation").
+    Consumer: `u_wall` uses this to route cavity walls to the Filled-
+    cavity row of Table 6 (in lieu of the bucketed cascade). For the
+    non-cavity `wall_ins_present` gate, `heat_transmission_from_cert`
+    further restricts this to genuine (non-assumed) retrofit via its
+    local `_described_as_retrofit_insulated`.
     """
     if description is None:
         return False
@@ -69,6 +66,41 @@ def _described_as_insulated(description: Optional[str]) -> bool:
     return "insulated" in desc or "partial insulation" in desc
 
 
+def _cavity_described_as_filled(description: Optional[str]) -> bool:
+    """True when an as-built cavity wall's description asserts the cavity is
+    insulated/filled, routing it to the Table 6 "Filled cavity" row.
+
+    Distinguishes the three as-built cavity states the EPC renders by age
+    band when wall_insulation_type=4 ("as-built / assumed"):
+
+      - "...insulated (assumed)"          → Filled cavity (assessor judges
+                                            the cavity filled but lodges no
+                                            thickness)
+      - "...partial insulation (assumed)" → "Cavity as built" row (the
+                                            as-built partial fill of the age
+                                            band, NOT a retrofit cavity fill)
+      - "...no insulation (assumed)"      → "Cavity as built" row
+
+    Narrower than `_described_as_insulated`: it excludes the "partial
+    insulation" substring so a "partial insulation (assumed)" cavity stays on
+    the as-built row. RdSAP 10 Table 6 (England) "Cavity as built" band F =
+    1.0 vs "Filled cavity" band F = 0.40 — for an as-built band-F cavity the
+    filled row understates heat loss by 2.5x. A genuine retrofit fill is
+    lodged distinctly as "Cavity wall, filled cavity"
+    (wall_insulation_type=2), handled by the explicit-code branch.
+
+    Real-cert evidence: golden cert 0390-2954-3640 (detached, band F, cavity
+    type 4, "partial insulation (assumed)") closes all four SAP metrics on
+    the as-built 1.0 row; the filled 0.40 row under-counts PE by ~28 kWh/m².
+    """
+    if description is None:
+        return False
+    desc = description.lower()
+    if "no insulation" in desc:
+        return False
+    return "insulated" in desc
+
+
 # ---------------------------------------------------------------------------
 # Country
 # ---------------------------------------------------------------------------
@@ -145,6 +177,43 @@ WALL_INSULATION_CAVITY_PLUS_INTERNAL: Final[int] = 7
 # (cavity + external/internal insulation).
 _WALL_INSULATION_LAMBDA_W_PER_MK: Final[float] = 0.04
 
+# RdSAP 10 §5.8 (page 41) — when documentary evidence lodges the insulation
+# thermal conductivity, the R-value calc uses it instead of the 0.04 default.
+# The spec offers three λ: 0.04 (mineral wool / EPS, the default), 0.03 (XPS),
+# 0.025 (PUR / PIR / phenolic). The GOV.UK API surfaces a coded value
+# (`wall_insulation_thermal_conductivity`); code 1 = the default 0.04 (the
+# only code observed — cert 2130 Ext1, whose documentary-evidence path does
+# not fire as no wall thickness is lodged, so the value is captured but
+# unused there). Other codes raise until a worksheet-backed fixture confirms
+# their λ — the same incremental-coverage discipline as the glazing-type map.
+_WALL_INSULATION_CONDUCTIVITY_CODE_TO_LAMBDA: Final[dict[int, float]] = {
+    1: 0.04,
+}
+
+
+def _resolve_wall_insulation_lambda_w_per_mk(
+    conductivity: "str | int | None",
+) -> float:
+    """Resolve the insulation λ (W/m·K) for the §5.8 documentary-evidence
+    R-value calc. Absent / "Unknown" → the 0.04 default; a mapped integer
+    code → its λ; an unmapped integer code raises so the enum is confirmed
+    against a worksheet rather than silently mis-factored."""
+    if conductivity is None:
+        return _WALL_INSULATION_LAMBDA_W_PER_MK
+    if isinstance(conductivity, str):
+        text = conductivity.strip()
+        if not text or text.lower() == "unknown" or not text.isdigit():
+            return _WALL_INSULATION_LAMBDA_W_PER_MK
+        conductivity = int(text)
+    lam = _WALL_INSULATION_CONDUCTIVITY_CODE_TO_LAMBDA.get(conductivity)
+    if lam is None:
+        raise ValueError(
+            "unmapped wall_insulation_thermal_conductivity code "
+            f"{conductivity!r}; add its RdSAP 10 §5.8 λ "
+            "(0.04 / 0.03 / 0.025 W/m·K) once a worksheet confirms it"
+        )
+    return lam
+
 # RdSAP10 §5.8 final note + Table 14 page 41: "For drylining including
 # laths and plaster use Rinsulation = 0.17 m²K/W." Applied additively to
 # the base U-value of an otherwise-uninsulated wall when the cert lodges
@@ -457,6 +526,7 @@ def u_wall(
     dry_lined: bool = False,
     curtain_wall_age: Optional[str] = None,
     wall_thickness_mm: Optional[int] = None,
+    wall_insulation_thermal_conductivity: "str | int | None" = None,
 ) -> float:
     """RdSAP10 wall U-value in W/m^2K, never null.
 
@@ -569,7 +639,10 @@ def u_wall(
     ):
         u0 = _u_brick_thin_wall_age_a_to_e(wall_thickness_mm)
         r_ins = _r_insulation_table_14(
-            insulation_thickness_mm, _WALL_INSULATION_LAMBDA_W_PER_MK,
+            insulation_thickness_mm,
+            _resolve_wall_insulation_lambda_w_per_mk(
+                wall_insulation_thermal_conductivity
+            ),
         )
         u_unrounded = 1.0 / (1.0 / u0 + r_ins)
         return float(
@@ -591,7 +664,9 @@ def u_wall(
         # for column alignment). Cascade-internal HLC then uses the
         # rounded U so net wall HLC matches `A × U_2dp` exactly.
         u_filled = _CAVITY_FILLED_ENG[age_idx]
-        r_ins = (insulation_thickness_mm / 1000.0) / _WALL_INSULATION_LAMBDA_W_PER_MK
+        r_ins = (insulation_thickness_mm / 1000.0) / _resolve_wall_insulation_lambda_w_per_mk(
+            wall_insulation_thermal_conductivity
+        )
         u_unrounded = 1.0 / (1.0 / u_filled + r_ins)
         # Half-up 2-d.p. round so 0.2545 → 0.25, matching the dr87
         # worksheet's column-display behaviour (used downstream in A×U).
@@ -600,7 +675,7 @@ def u_wall(
         )
     if wall_type == WALL_CAVITY and (
         wall_insulation_type == WALL_INSULATION_FILLED_CAVITY
-        or _described_as_insulated(description)
+        or _cavity_described_as_filled(description)
     ):
         return _CAVITY_FILLED_ENG[age_idx]
     bucket = _insulation_bucket(insulation_thickness_mm, insulation_present)
@@ -688,6 +763,8 @@ def u_roof(
     insulation_thickness_mm: Optional[int],
     description: Optional[str] = None,
     is_flat_roof: bool = False,
+    is_sloping_ceiling: bool = False,
+    is_pitched_sloping_ceiling: bool = False,
 ) -> float:
     """RdSAP10 roof U-value in W/m^2K, never null.
 
@@ -701,6 +778,29 @@ def u_roof(
     3. Table 18 age-band default — column (1) "Pitched, insulation between
        joists" by default; column (3) "Flat roof" when `is_flat_roof=True`.
        Spec §5.11 Table 18 page 45.
+
+    `is_sloping_ceiling` flags a pitched roof whose ceiling follows the
+    slope (a "Pitched, sloping ceiling" or "Pitched (vaulted ceiling)"
+    construction — RdSAP roof_construction codes 8 and 5). Such a roof has
+    no loft / ceiling-joist void, so an "NI" lodgement (parsed to 0) +
+    "insulated (assumed)" description means unknown-thickness-with-insulation,
+    NOT the §5.11.4 retrofit-50 mm joist row (0.68) a normal pitched-with-
+    loft roof would take. It instead takes the Table 18 column (1) age-band
+    default (band J = 0.16) — the same value a vaulted roof lodged "ND"
+    (thickness None) already reaches by falling through. The 33 cohort-2
+    "ND" vaulted certs (code 5, band D → 0.40 = col 1) are the evidence.
+
+    `is_pitched_sloping_ceiling` is the narrower code-8 ("Pitched, sloping
+    ceiling") signal for the AS-BUILT case (insulation lodged "As Built",
+    parsed to thickness None — distinct from the "NI"/"ND" unknown case
+    above). Per RdSAP 10 roof-input item 5-5 ("Sloping ceiling insulation
+    ... as built → Table 18") and Table 18 note (b) ("applies also to roof
+    with sloping ceiling"), an as-built sloping ceiling takes the column
+    (3) age-band default (band F = 0.68, band L = 0.18), NOT the column (1)
+    loft-joist default (band F = 0.40, band L = 0.16). Vaulted ceilings
+    (code 5) are deliberately excluded — they stay on column (1) per the
+    cohort evidence above. Worksheet-validated by simulated case 15 (the
+    7536 replica): Ext1 band L → 0.18, Ext2 band F → 0.68.
     """
     measured = _measured_u_from_description(description)
     if measured is not None:
@@ -708,6 +808,20 @@ def u_roof(
         # ("Average thermal transmittance X W/m²K"); spec §5.11 opening
         # clause defers to the assessor's value when present.
         return measured
+    if (
+        is_sloping_ceiling
+        and age_band is not None
+        and insulation_thickness_mm == 0
+        and _described_as_insulated(description)
+    ):
+        # RdSAP 10 §5.11 Table 18 page 45 — a vaulted/sloping ceiling has no
+        # ceiling-joist void, so the "NI" sentinel (parsed to 0) +
+        # "insulated (assumed)" is unknown-thickness-with-insulation, not
+        # 0 mm uninsulated. It must NOT fall to the §5.11.4 retrofit-50 mm
+        # joist row (0.68) below; it takes the column (1) age-band default
+        # (band J = 0.16), matching the cohort's "ND" (thickness None)
+        # vaulted roofs which already reach col (1) by falling through.
+        return _ROOF_BY_AGE.get(age_band.upper(), 0.4)
     if insulation_thickness_mm == 0 and _described_as_insulated(description):
         # Spec §5.11.4 (page 44 footnote): "If retrofit insulation
         # present of unknown thickness use 50 mm". The cert encodes
@@ -731,6 +845,15 @@ def u_roof(
             return _ROOF_BY_THICKNESS[1][1]  # 1.50 W/m^2K (12mm row)
     if age_band is None:
         return 0.4
+    if is_pitched_sloping_ceiling:
+        # RdSAP 10 §5.11 Table 18 page 45 column (3) + roof-input item 5-5:
+        # an as-built "Pitched, sloping ceiling" (code 8) with no measured
+        # thickness takes the column (3) age-band default, not the column
+        # (1) loft-joist default. Note (b): column (3) "applies also to
+        # roof with sloping ceiling". (Pre-1950 bands reach the same value
+        # via the mapper's thickness=0 → Table 16 row-0 2.30 override, so
+        # this branch carries the post-1950 bands where col 1 ≠ col 3.)
+        return _FLAT_ROOF_BY_AGE.get(age_band.upper(), 0.4)
     if is_flat_roof:
         return _FLAT_ROOF_BY_AGE.get(age_band.upper(), 0.4)
     return _ROOF_BY_AGE.get(age_band.upper(), 0.4)

domain/sap10_ml/tests/test_rdsap_uvalues.py

@@ -165,18 +165,28 @@ def test_u_wall_cavity_as_built_no_insulation_stays_at_table6_cavity_as_built_ro
     assert result == pytest.approx(1.5, abs=0.001)
 
 
-def test_u_wall_cavity_as_built_partial_insulation_routes_to_filled_cavity_row() -> None:
-    # Arrange — 147 corpus certs lodge "Cavity wall, as built, partial
-    # insulation (assumed)" with wall_insulation_type=4. The legacy
-    # production map (recommendations/rdsap_tables.py:753) routes these
-    # to "Filled cavity" — same destination as the "insulated (assumed)"
-    # case. We match that interpretation for parity with the cert
-    # assessor and the production recommendation engine.
+def test_u_wall_cavity_as_built_partial_insulation_routes_to_as_built_row() -> None:
+    # Arrange — a cavity lodged "Cavity wall, as built, partial insulation
+    # (assumed)" with wall_insulation_type=4 is in its AS-BUILT state (the
+    # partial fill of the age band), NOT a retrofit cavity fill. Per
+    # RdSAP 10 Table 6 (England) it uses the "Cavity as built" row, not
+    # "Filled cavity": band D = 1.5 (as built) vs 0.7 (filled). A genuine
+    # fill lodges the distinct "Cavity wall, filled cavity"
+    # (wall_insulation_type=2), caught by the explicit-code branch.
+    #
+    # Slice S0380.210 corrected this: the prior routing to "Filled cavity"
+    # mirrored a legacy production map, but golden cert 0390-2954-3640
+    # (band F, cavity type 4, "partial insulation (assumed)") closes all
+    # four SAP metrics on the as-built row (band F = 1.0) and under-counts
+    # PE by ~28 kWh/m² on the filled row — the legacy parity was a latent
+    # bug at bands A-H (bands I-M coincide per the Table 6 † footnote).
+    # The "insulated (assumed)" variant still routes to filled (see the
+    # heat_transmission `_cavity_described_as_filled` sibling test).
 
     # Act
     result = u_wall(
         country=Country.ENG,
-        age_band="D",  # 1950-1966 — typical partial-fill retrofit cohort
+        age_band="D",  # 1950-1966 — as-built ≠ filled at this band
         construction=WALL_CAVITY,
         insulation_thickness_mm=None,
         insulation_present=False,
@@ -184,8 +194,8 @@ def test_u_wall_cavity_as_built_partial_insulation_routes_to_filled_cavity_row()
         description="Cavity wall, as built, partial insulation (assumed)",
     )
 
-    # Assert — Filled-cavity row at band D = 0.7 W/m²K.
-    assert result == pytest.approx(0.7, abs=0.001)
+    # Assert — Cavity-as-built row at band D = 1.5 W/m²K (not filled 0.7).
+    assert abs(result - 1.5) <= 0.001
 
 
 def test_u_wall_description_without_transmittance_phrase_routes_through_cascade() -> None:
@@ -841,6 +851,54 @@ def test_u_roof_unknown_age_band_falls_back_to_mid_range() -> None:
     assert result == pytest.approx(0.4, abs=0.001)
 
 
+def test_u_roof_vaulted_ni_unknown_band_j_uses_col1_age_band_not_50mm() -> None:
+    # Arrange — a pitched roof with a vaulted/sloping ceiling (no joist
+    # void) lodged with insulation thickness "NI" (Not Indicated, parsed
+    # to 0) + an "insulated (assumed)" description. For a NORMAL pitched
+    # roof this hits the §5.11.4 "retrofit 50 mm" override (U=0.68, the
+    # Table 16 joist row) — but a vaulted/sloping ceiling has no joist
+    # void, so RdSAP 10 Table 18 routes it to the column (1) age-band
+    # default: band J = 0.16 W/m²K (NOT 0.68). This is the same value a
+    # vaulted roof lodged "ND" (thickness None) already reaches by falling
+    # through to the age-band default.
+    #
+    # Cohort-validated: 33 cohort-2 certs lodge "ND" vaulted roofs
+    # (roof_construction=5, band D) that pin to worksheet U=0.40 = col (1).
+    # Closes golden cert 0240's Ext1 vaulted roof (code 5, NI, band J)
+    # which the cascade returned at 0.68 (offsetting the wall under-count
+    # fixed in S0380.209).
+
+    # Act
+    result = u_roof(
+        country=Country.ENG,
+        age_band="J",
+        insulation_thickness_mm=0,  # parsed from "NI"
+        description="Pitched, insulated (assumed)",
+        is_sloping_ceiling=True,
+    )
+
+    # Assert
+    assert abs(result - 0.16) <= 1e-4
+
+
+def test_u_roof_normal_pitched_ni_insulated_still_returns_50mm_per_5_11_4() -> None:
+    # Arrange — regression guard: the is_sloping_ceiling flag defaults
+    # False, so a NORMAL pitched roof (with loft) lodged NI + "insulated
+    # (assumed)" must STILL hit the §5.11.4 retrofit-50 mm row (U=0.68).
+    # Same inputs as the sloping test above minus is_sloping_ceiling.
+
+    # Act
+    result = u_roof(
+        country=Country.ENG,
+        age_band="J",
+        insulation_thickness_mm=0,
+        description="Pitched, insulated (assumed)",
+    )
+
+    # Assert
+    assert abs(result - 0.68) <= 1e-4
+
+
 def test_u_roof_flat_age_band_d_returns_table18_col3_value() -> None:
     # Arrange — RdSAP 10 §5.11 Table 18 page 45 column (3) "Flat roof":
     # age band D, thickness unknown → U = 2.30 W/m²K. Column (1)
@@ -887,6 +945,66 @@ def test_u_roof_flat_age_band_l_returns_table18_col3_value() -> None:
     assert abs(result - 0.18) <= 1e-4
 
 
+def test_u_roof_pitched_sloping_ceiling_as_built_band_f_uses_col3() -> None:
+    # Arrange — RdSAP 10 §5.11 Table 18 page 45 + roof-input item 5-5
+    # ("Sloping ceiling insulation ... unknown / as built → Table 18").
+    # A "Pitched, sloping ceiling" roof (roof_construction code 8) with an
+    # "As Built" insulation lodgement (no measured thickness → None) takes
+    # the Table 18 column (3) age-band default, NOT the column (1)
+    # "insulation between joists" default. Note (b) on column (3) states it
+    # "applies also to roof with sloping ceiling". For age band F the
+    # column (3) value is 0.68 W/m²K (vs column (1) 0.40 — the loft-joist
+    # assumption that is wrong for a sloping ceiling with no joist void).
+    #
+    # Worksheet-validated: simulated case 15 (7536 replica) lodges Ext2 as
+    # band F "PS Pitched, sloping ceiling, As Built"; its P960 worksheet
+    # pins `External roof Ext2 … 0.68`, and the full-cascade roof HLC and
+    # SAP match Elmhurst exactly only with column (3).
+
+    # Act
+    result = u_roof(
+        country=Country.ENG, age_band="F", insulation_thickness_mm=None,
+        is_pitched_sloping_ceiling=True,
+    )
+
+    # Assert
+    assert abs(result - 0.68) <= 1e-4
+
+
+def test_u_roof_pitched_sloping_ceiling_as_built_band_l_uses_col3() -> None:
+    # Arrange — same rule at band L (2012-2022): Table 18 column (3) gives
+    # 0.18 W/m²K, where columns (2)/(3) coincide. Simulated case 15's Ext1
+    # (band L PS sloping ceiling, As Built) pins worksheet U=0.18 (vs the
+    # column (1) value 0.16 the cascade returned pre-fix).
+
+    # Act
+    result = u_roof(
+        country=Country.ENG, age_band="L", insulation_thickness_mm=None,
+        is_pitched_sloping_ceiling=True,
+    )
+
+    # Assert
+    assert abs(result - 0.18) <= 1e-4
+
+
+def test_u_roof_vaulted_nd_unknown_band_d_still_col1_not_col3() -> None:
+    # Arrange — regression guard for the discriminator: a code-5 "vaulted"
+    # roof lodged "ND" (thickness None) is the UNKNOWN-insulation case and
+    # must stay on Table 18 column (1) — band D = 0.40 — per the 33
+    # cohort-2 vaulted certs (S0380.211). The col (3) routing fires only
+    # for code-8 "Pitched, sloping ceiling" (is_pitched_sloping_ceiling),
+    # NOT for vaulted ceilings, so this defaults False here and resolves
+    # to column (1) 0.40, NOT column (3) 2.30.
+
+    # Act
+    result = u_roof(
+        country=Country.ENG, age_band="D", insulation_thickness_mm=None,
+    )
+
+    # Assert
+    assert abs(result - 0.40) <= 1e-4
+
+
 def test_u_roof_description_no_insulation_overrides_age_band_default() -> None:
     # Arrange — surveyor description on a Victorian roof says uninsulated;
     # Table 18 age-B default (0.40) is far too optimistic. Table 16 row 0mm
@@ -1752,3 +1870,59 @@ def test_u_floor_matches_section_5_12_formula_for_cohort_geometry(
 
     # Assert
     assert abs(u - expected_u) < 1e-4
+
+
+def test_resolve_wall_insulation_lambda_absent_uses_default() -> None:
+    # Arrange — no lodged conductivity → RdSAP 10 §5.8 default 0.04 W/m·K.
+    from domain.sap10_ml.rdsap_uvalues import (
+        _resolve_wall_insulation_lambda_w_per_mk,
+    )
+
+    # Act
+    lam = _resolve_wall_insulation_lambda_w_per_mk(None)
+
+    # Assert
+    assert abs(lam - 0.04) <= 1e-9
+
+
+def test_resolve_wall_insulation_lambda_unknown_string_uses_default() -> None:
+    # Arrange — a non-numeric "Unknown" lodgement defers to the default.
+    from domain.sap10_ml.rdsap_uvalues import (
+        _resolve_wall_insulation_lambda_w_per_mk,
+    )
+
+    # Act
+    lam = _resolve_wall_insulation_lambda_w_per_mk("Unknown")
+
+    # Assert
+    assert abs(lam - 0.04) <= 1e-9
+
+
+def test_resolve_wall_insulation_lambda_code_1_is_default_mineral_wool() -> None:
+    # Arrange — code 1 = the §5.8 default λ=0.04 (mineral wool / EPS);
+    # cert 2130 Ext1 lodges this. Numeric-string form resolves identically.
+    from domain.sap10_ml.rdsap_uvalues import (
+        _resolve_wall_insulation_lambda_w_per_mk,
+    )
+
+    # Act
+    lam_int = _resolve_wall_insulation_lambda_w_per_mk(1)
+    lam_str = _resolve_wall_insulation_lambda_w_per_mk("1")
+
+    # Assert
+    assert abs(lam_int - 0.04) <= 1e-9
+    assert abs(lam_str - 0.04) <= 1e-9
+
+
+def test_resolve_wall_insulation_lambda_unmapped_code_raises() -> None:
+    # Arrange — an unmapped code must raise (incremental-coverage gate)
+    # rather than silently mis-factor the R-value.
+    import pytest as _pytest
+
+    from domain.sap10_ml.rdsap_uvalues import (
+        _resolve_wall_insulation_lambda_w_per_mk,
+    )
+
+    # Act / Assert
+    with _pytest.raises(ValueError):
+        _resolve_wall_insulation_lambda_w_per_mk(2)

infrastructure/postgres/epc_property_table.py

@@ -549,7 +549,15 @@ class EpcBuildingPartModel(SQLModel, table=True):
     building_part_number: Optional[int] = Field(default=None)
     wall_dry_lined: Optional[bool] = Field(default=None)
     wall_thickness_mm: Optional[int] = Field(default=None)
-    wall_insulation_thickness: Optional[str] = Field(default=None)
+    # Union[str, int] — int mm when the API lodges
+    # `wall_insulation_thickness == "measured"` (resolved by
+    # `_api_resolve_wall_insulation_thickness`), else the lodged string
+    # ("NI", a numeric string, ...). JSONB to preserve int vs str on
+    # round-trip, exactly like the sibling `roof_insulation_thickness` /
+    # `flat_roof_insulation_thickness`.
+    wall_insulation_thickness: Optional[Union[str, int]] = Field(
+        default=None, sa_column=Column(JSONB, nullable=True)
+    )
     floor_heat_loss: Optional[int] = Field(default=None)
     floor_insulation_thickness: Optional[str] = Field(default=None)
     flat_roof_insulation_thickness: Optional[Union[str, int]] = Field(

scripts/analyse_api_sap_clusters.py

@@ -0,0 +1,102 @@
+"""Group API-path SAP error by property + heating type to find clusters.
+
+WHAT THIS IS FOR
+----------------
+The headline number from `eval_api_sap_accuracy.py` tells you HOW accurate the
+API path is; this tells you WHERE the error lives so you can prioritise. It
+buckets the cached sample's per-cert SAP error (continuous vs lodged) by:
+  - property type (house / flat / bungalow / maisonette / park home),
+  - real PV presence,
+  - heating identity (main_heating_category + whether a PCDB index is lodged),
+and prints n / mean|err| / %<0.5 per group, plus red flags (negative or
+extreme-low SAP). The load-bearing cut is heating: e.g. electric storage
+heaters (cat 7) and room heaters (cat 10) are the worst clusters, which points
+the next worksheet-backed fix at those systems.
+
+USAGE
+-----
+    PYTHONPATH=/workspaces/model python scripts/analyse_api_sap_clusters.py
+
+Reads the cache written by `fetch_2026_epc_sample.py` (default
+`/tmp/epc_2026_sample`, overridable via `EPC_SAMPLE_CACHE`).
+"""
+import os
+import json
+import math
+from collections import defaultdict
+from pathlib import Path
+
+from datatypes.epc.domain.mapper import EpcPropertyDataMapper
+from domain.sap10_calculator.calculator import calculate_sap_from_inputs
+from domain.sap10_calculator.rdsap.cert_to_inputs import SAP_10_2_SPEC_PRICES, cert_to_inputs
+
+CACHE = Path(os.environ.get("EPC_SAMPLE_CACHE", "/tmp/epc_2026_sample"))
+PROP = {"0": "House", "1": "Bungalow", "2": "Flat", "3": "Maisonette", "4": "Park home"}
+
+
+def real_pv(doc):
+    """True only for a genuine PV array — `none_or_no_details` / 0% is not PV."""
+    es = doc.get("sap_energy_source", {}) or {}
+    pv = es.get("photovoltaic_supply")
+    if not isinstance(pv, dict):
+        return False
+    if set(pv.keys()) <= {"none_or_no_details"}:
+        nod = pv.get("none_or_no_details") or {}
+        return bool(nod.get("percent_roof_area"))
+    return True
+
+
+def heat_identity(doc):
+    h = doc.get("sap_heating", {}) or {}
+    mh = (h.get("main_heating_details") or [{}])
+    m0 = mh[0] if mh else {}
+    return m0.get("main_heating_index_number"), m0.get("main_heating_category")
+
+
+def main():
+    rows = []
+    for f in sorted(CACHE.glob("????-????-????-????-????.json")):
+        doc = json.loads(f.read_text())
+        lodged = doc.get("energy_rating_current")
+        try:
+            epc = EpcPropertyDataMapper.from_api_response(doc)
+            cont = calculate_sap_from_inputs(
+                cert_to_inputs(epc, prices=SAP_10_2_SPEC_PRICES)
+            ).sap_score_continuous
+        except Exception:
+            continue
+        if lodged is None or not math.isfinite(cont):
+            continue
+        idx, cat = heat_identity(doc)
+        rows.append(dict(
+            cert=f.stem, ae=abs(cont - lodged), cont=cont, lodged=lodged,
+            prop=PROP.get(str(doc.get("property_type")), str(doc.get("property_type"))),
+            pv=real_pv(doc), idx=idx, cat=cat,
+            neg=(cont < 0), low_lodged=(lodged <= 20),
+        ))
+    n = len(rows)
+
+    def grp(keyfn, label):
+        g = defaultdict(list)
+        for r in rows:
+            g[keyfn(r)].append(r["ae"])
+        print(f"\n-- mean|err| by {label} (n, mean|err|, %<0.5) --")
+        for k, v in sorted(g.items(), key=lambda kv: -sum(kv[1]) / len(kv[1])):
+            if len(v) < 5:
+                continue
+            p = 100 * sum(1 for x in v if x < 0.5) / len(v)
+            print(f"   {str(k):28s} n={len(v):4d}  mean={sum(v) / len(v):6.2f}  <0.5={p:4.1f}%")
+
+    print(f"computed n={n}")
+    grp(lambda r: r["prop"], "property type")
+    grp(lambda r: "PV" if r["pv"] else "no-PV", "real PV presence")
+    grp(lambda r: f"cat={r['cat']},idx={'Y' if r['idx'] else '-'}", "heating identity")
+
+    neg = [r for r in rows if r["neg"]]
+    loww = [r for r in rows if r["low_lodged"]]
+    print(f"\nRED FLAGS: negative continuous SAP: {len(neg)} | lodged<=20 (extreme): {len(loww)}")
+    print("  negative-SAP certs:", [r["cert"] for r in neg][:15])
+
+
+if __name__ == "__main__":
+    main()

scripts/eval_api_sap_accuracy.py

@@ -0,0 +1,169 @@
+"""Score the SAP10 calculator's API path against a cached EPC sample.
+
+WHAT THIS IS FOR
+----------------
+Measures how well the API front-end (`from_api_response` → `cert_to_inputs`
+→ continuous SAP) reproduces each cert's lodged rounded SAP
+(`energy_rating_current`) across the sample built by
+`fetch_2026_epc_sample.py`. This is the headline accuracy gauge for raw-API
+behaviour on an unbiased population.
+
+Each cert lands in one bucket:
+  - computed            — ran end-to-end; SAP error recorded.
+  - unsupported_schema  — pre-21 schema the mapper doesn't support (skip).
+  - raise:<Exc>         — mapper raised (UnmappedApiCode etc.) — a gap to fix.
+  - calc_raise:<Exc>    — calculator raised (UnmappedSapCode etc.) — a gap.
+
+OUTPUT
+------
+  - Category counts + the raise breakdown with example certs (what to fix).
+  - For computed certs: % within 0.5 / 1 / 2 / 5 SAP, median/mean/p90/p99/max
+    |err|, the signed mean (over- vs under-rating), abs-err histogram.
+  - The 40 worst offenders with diagnostic columns (to prioritise).
+  - A full per-cert CSV at <cache>/_results.csv for ad-hoc slicing.
+
+USAGE
+-----
+    PYTHONPATH=/workspaces/model python scripts/eval_api_sap_accuracy.py
+
+Reads the cache written by `fetch_2026_epc_sample.py` (default
+`/tmp/epc_2026_sample`, overridable via `EPC_SAMPLE_CACHE`).
+"""
+import os
+import json
+import csv
+import math
+from collections import Counter, defaultdict
+from pathlib import Path
+
+from datatypes.epc.domain.mapper import EpcPropertyDataMapper
+from domain.sap10_calculator.calculator import calculate_sap_from_inputs
+from domain.sap10_calculator.rdsap.cert_to_inputs import SAP_10_2_SPEC_PRICES, cert_to_inputs
+
+CACHE = Path(os.environ.get("EPC_SAMPLE_CACHE", "/tmp/epc_2026_sample"))
+
+
+def diag(doc):
+    """A few raw-JSON fields that help explain a cert's error at a glance."""
+    es = doc.get("sap_energy_source", {}) or {}
+    h = doc.get("sap_heating", {}) or {}
+    mh = (h.get("main_heating_details") or [{}])
+    mh0 = mh[0] if mh else {}
+    pv = es.get("photovoltaic_supply")
+    return {
+        "schema": doc.get("schema_type"),
+        "prop_type": doc.get("property_type"),
+        "built_form": doc.get("built_form"),
+        "age_band": doc.get("construction_age_band"),
+        "mains_gas": es.get("mains_gas"),
+        "main_heat_cat": mh0.get("main_heating_category"),
+        "main_heat_idx": mh0.get("main_heating_index_number"),
+        "n_bps": len(doc.get("sap_building_parts") or []),
+        "lodged_band": doc.get("current_energy_efficiency_band"),
+    }
+
+
+def main():
+    files = sorted(CACHE.glob("????-????-????-????-????.json"))
+    rows = []
+    cat = Counter()
+    exc_examples = defaultdict(list)
+    for f in files:
+        cert = f.stem
+        try:
+            doc = json.loads(f.read_text())
+        except Exception:
+            cat["bad_json"] += 1
+            continue
+        lodged = doc.get("energy_rating_current")
+        try:
+            epc = EpcPropertyDataMapper.from_api_response(doc)
+        except ValueError as e:
+            if "Unsupported EPC schema" in str(e):
+                cat["unsupported_schema"] += 1
+            else:
+                cat["raise:ValueError"] += 1
+                exc_examples["ValueError:" + str(e)[:60]].append(cert)
+            continue
+        except Exception as e:
+            ename = type(e).__name__
+            cat[f"raise:{ename}"] += 1
+            exc_examples[f"{ename}:{str(e)[:60]}"].append(cert)
+            continue
+        if lodged is None:
+            cat["no_lodged_sap"] += 1
+            continue
+        try:
+            cont = calculate_sap_from_inputs(
+                cert_to_inputs(epc, prices=SAP_10_2_SPEC_PRICES)
+            ).sap_score_continuous
+        except Exception as e:
+            ename = type(e).__name__
+            cat[f"calc_raise:{ename}"] += 1
+            exc_examples[f"calc:{ename}:{str(e)[:50]}"].append(cert)
+            continue
+        if not math.isfinite(cont):
+            cat["non_finite"] += 1
+            continue
+        err = cont - lodged
+        cat["computed"] += 1
+        rows.append({
+            "cert": cert, "our_cont": round(cont, 4), "lodged": lodged,
+            "err": round(err, 4), "abs_err": round(abs(err), 4), **diag(doc),
+        })
+
+    if rows:
+        keys = list(rows[0].keys())
+        with open(CACHE / "_results.csv", "w", newline="") as fh:
+            w = csv.DictWriter(fh, fieldnames=keys)
+            w.writeheader()
+            w.writerows(rows)
+
+    n = len(rows)
+    print("=" * 70)
+    print(f"SAMPLE: {len(files)} cached certs | categories:")
+    for k, v in cat.most_common():
+        print(f"   {k:28s} {v}")
+    if n == 0:
+        return
+    abs_errs = sorted(r["abs_err"] for r in rows)
+
+    def pct(thr):
+        return 100.0 * sum(1 for r in rows if r["abs_err"] < thr) / n
+
+    print("=" * 70)
+    print(f"COMPUTED: {n} certs (continuous SAP vs lodged rounded)")
+    print(f"   % |err| < 0.5  : {pct(0.5):.1f}%   <-- headline")
+    print(f"   % |err| < 1.0  : {pct(1.0):.1f}%")
+    print(f"   % |err| < 2.0  : {pct(2.0):.1f}%")
+    print(f"   % |err| < 5.0  : {pct(5.0):.1f}%")
+    print(f"   median |err|   : {abs_errs[n // 2]:.3f}")
+    print(f"   mean   |err|   : {sum(abs_errs) / n:.3f}")
+    print(f"   p90 |err|      : {abs_errs[int(n * 0.90)]:.3f}")
+    print(f"   p99 |err|      : {abs_errs[int(n * 0.99)]:.3f}")
+    print(f"   max |err|      : {abs_errs[-1]:.3f}")
+    signed = [r["err"] for r in rows]
+    print(f"   mean signed err: {sum(signed) / n:+.3f} (we - lodged; +ve = we over-rate)")
+    print("   abs-err buckets:")
+    for lo, hi in [(0, 0.5), (0.5, 1), (1, 2), (2, 5), (5, 10), (10, 1e9)]:
+        c = sum(1 for r in rows if lo <= r["abs_err"] < hi)
+        print(f"      [{lo:>4}, {hi:>4}) : {c:4d}  ({100 * c / n:4.1f}%)")
+    print("=" * 70)
+    print("TOP 40 LARGEST |err| (prioritise these):")
+    worst = sorted(rows, key=lambda r: -r["abs_err"])[:40]
+    print(f"   {'cert':22s} {'err':>7s} {'our':>6s} {'lodg':>4s}  prop bf age  gas cat/idx bps")
+    for r in worst:
+        print(f"   {r['cert']:22s} {r['err']:+7.2f} {r['our_cont']:6.1f} {r['lodged']:4d}  "
+              f"{str(r['prop_type']):>4s} {str(r['built_form']):>2s} {str(r['age_band'])[:3]:>3s} "
+              f"{str(r['mains_gas']):>3s} {str(r['main_heat_cat']):>3s}/{str(r['main_heat_idx']):>6s} "
+              f"{r['n_bps']}")
+    if exc_examples:
+        print("=" * 70)
+        print("RAISE/ERROR EXAMPLES (mapper/calculator gaps — also prioritise):")
+        for k, v in sorted(exc_examples.items(), key=lambda kv: -len(kv[1]))[:20]:
+            print(f"   [{len(v):3d}] {k}   e.g. {v[0]}")
+    print(f"\nFull per-cert CSV -> {CACHE / '_results.csv'}")
+
+
+if __name__ == "__main__":
+    main()

scripts/fetch_2026_epc_sample.py

@@ -0,0 +1,145 @@
+"""Fetch a random sample of domestic EPC JSONs from the GOV.UK EPB register.
+
+WHAT THIS IS FOR
+----------------
+Wide-scale accuracy testing of the SAP10 calculator's API front-end against
+real-world certificates (not the curated golden cohort, which masks raw-API
+behaviour). This script builds the *input corpus*: it samples certificate
+numbers uniformly at random across a date window, then downloads each cert's
+full schema-21 ``data`` payload (the exact shape
+``EpcPropertyDataMapper.from_api_response`` consumes) into a local cache.
+
+Pair it with:
+  - ``eval_api_sap_accuracy.py``   — % within 0.5 SAP, worst offenders, raises.
+  - ``analyse_api_sap_clusters.py`` — error grouped by heating type / property.
+
+HOW THE SAMPLE IS DRAWN
+-----------------------
+The register's ``/api/domestic/search`` endpoint is date-windowed and paged
+(``date_start``/``date_end``/``current_page``/``page_size``); results are
+ordered by registration date, so picking random PAGES across the whole window
+gives an unbiased spread over dates, regions and property types. Each chosen
+cert number is then resolved to its full JSON via ``/api/certificate``.
+
+USAGE
+-----
+    PYTHONPATH=/workspaces/model python scripts/fetch_2026_epc_sample.py
+
+Resumable — re-running skips certs already cached, so it's safe to interrupt.
+Token is read from ``backend/.env`` (``OPEN_EPC_API_TOKEN``). NB the register
+rejects a ``date_end`` that includes today, so keep the window in the past.
+
+Tune the constants below (window, page count, target size, seed). The cache
+dir defaults to ``/tmp/epc_2026_sample`` and can be overridden with the
+``EPC_SAMPLE_CACHE`` env var.
+"""
+import os
+import json
+import time
+import random
+import threading
+from pathlib import Path
+from concurrent.futures import ThreadPoolExecutor, as_completed
+
+import httpx
+from dotenv import load_dotenv
+
+load_dotenv("backend/.env")
+TOKEN = os.environ["OPEN_EPC_API_TOKEN"]
+BASE = "https://api.get-energy-performance-data.communities.gov.uk"
+H = {"Authorization": f"Bearer {TOKEN}", "Accept": "application/json"}
+CACHE = Path(os.environ.get("EPC_SAMPLE_CACHE", "/tmp/epc_2026_sample"))
+CACHE.mkdir(parents=True, exist_ok=True)
+
+# Sampling window + size. `date_end` must be strictly before today (the
+# register rejects "the date cannot include today"). TOTAL_PAGES is the
+# `totalPages` the search returns for this window at page_size=100 — re-probe
+# it if you change the window (it only needs to be an upper bound for the
+# random page draw; out-of-range pages just return fewer rows).
+WINDOW = {"date_start": "2026-01-01", "date_end": "2026-05-31"}
+TOTAL_PAGES = 7402
+N_PAGES = 14          # random pages to pull → N_PAGES * 100 candidate certs
+TARGET = 1200         # cap on how many full JSONs to fetch
+random.seed(2026)     # reproducible page draw
+
+
+def _get(url, params, timeout=20.0, tries=5):
+    """GET with retry/backoff on 429 + 5xx (honours Retry-After)."""
+    r = None
+    for i in range(tries):
+        try:
+            r = httpx.get(url, params=params, headers=H, timeout=timeout)
+        except httpx.HTTPError:
+            time.sleep(1.5 * (i + 1))
+            continue
+        if r.status_code == 429 or r.status_code >= 500:
+            ra = r.headers.get("Retry-After")
+            time.sleep(float(ra) if ra else 1.5 * (i + 1))
+            continue
+        return r
+    return r
+
+
+def sample_cert_numbers():
+    pages = sorted(random.sample(range(1, TOTAL_PAGES + 1), N_PAGES))
+    certs = {}
+    for p in pages:
+        r = _get(f"{BASE}/api/domestic/search", {**WINDOW, "current_page": p, "page_size": 100})
+        if r is None or not r.is_success:
+            print(f"  search page {p} -> {getattr(r, 'status_code', 'ERR')}")
+            continue
+        for row in r.json().get("data", []):
+            certs[row["certificateNumber"]] = row.get("registrationDate")
+        print(f"  page {p}: cumulative {len(certs)} certs")
+    return certs
+
+
+_lock = threading.Lock()
+_done = {"ok": 0, "404": 0, "err": 0}
+
+
+def fetch_one(cert):
+    out = CACHE / f"{cert}.json"
+    if out.exists():
+        with _lock:
+            _done["ok"] += 1
+        return
+    r = _get(f"{BASE}/api/certificate", {"certificate_number": cert})
+    if r is not None and r.status_code == 404:
+        with _lock:
+            _done["404"] += 1
+        return
+    if r is None or not r.is_success:
+        with _lock:
+            _done["err"] += 1
+        return
+    try:
+        payload = r.json()["data"]
+    except Exception:
+        with _lock:
+            _done["err"] += 1
+        return
+    out.write_text(json.dumps(payload))
+    with _lock:
+        _done["ok"] += 1
+        if _done["ok"] % 100 == 0:
+            print(f"  fetched {_done['ok']} (404={_done['404']} err={_done['err']})")
+
+
+def main():
+    print("sampling cert numbers...")
+    certs = sample_cert_numbers()
+    cert_list = list(certs)[:TARGET]
+    (CACHE / "_manifest.json").write_text(
+        json.dumps({"certs": cert_list, "window": WINDOW}, indent=2)
+    )
+    print(f"fetching {len(cert_list)} cert JSONs into {CACHE} ...")
+    t0 = time.time()
+    with ThreadPoolExecutor(max_workers=8) as ex:
+        list(as_completed([ex.submit(fetch_one, c) for c in cert_list]))
+    print(f"DONE in {time.time() - t0:.0f}s: ok={_done['ok']} 404={_done['404']} err={_done['err']}")
+    print(f"cached JSON files: {len(list(CACHE.glob('????-????-????-????-????.json')))}")
+
+
+if __name__ == "__main__":
+    main()

tests/domain/sap10_calculator/rdsap/fixtures/golden/0340-2467-9260-2006-6521.json

@@ -0,0 +1,516 @@
+{
+  "uprn": 77048251,
+  "roofs": [
+    {
+      "description": "Pitched, 300 mm loft insulation",
+      "energy_efficiency_rating": 5,
+      "environmental_efficiency_rating": 5
+    }
+  ],
+  "walls": [
+    {
+      "description": "Cavity wall, filled cavity",
+      "energy_efficiency_rating": 4,
+      "environmental_efficiency_rating": 4
+    }
+  ],
+  "floors": [
+    {
+      "description": "Solid, no insulation (assumed)",
+      "energy_efficiency_rating": 0,
+      "environmental_efficiency_rating": 0
+    }
+  ],
+  "status": "entered",
+  "tenure": 2,
+  "window": {
+    "description": "Fully double glazed",
+    "energy_efficiency_rating": 3,
+    "environmental_efficiency_rating": 3
+  },
+  "addendum": {
+    "addendum_numbers": [
+      15
+    ]
+  },
+  "lighting": {
+    "description": "Good lighting efficiency",
+    "energy_efficiency_rating": 4,
+    "environmental_efficiency_rating": 4
+  },
+  "postcode": "M22 1UR",
+  "hot_water": {
+    "description": "From main system",
+    "energy_efficiency_rating": 4,
+    "environmental_efficiency_rating": 4
+  },
+  "post_town": "MANCHESTER",
+  "built_form": 2,
+  "created_at": "2026-06-03 14:45:36",
+  "door_count": 2,
+  "region_code": 19,
+  "report_type": 2,
+  "sap_heating": {
+    "number_baths": 0,
+    "cylinder_size": 1,
+    "shower_outlets": [
+      {
+        "shower_wwhrs": 1,
+        "shower_outlet_type": 1
+      }
+    ],
+    "number_baths_wwhrs": 0,
+    "water_heating_code": 901,
+    "water_heating_fuel": 26,
+    "secondary_fuel_type": 29,
+    "main_heating_details": [
+      {
+        "has_fghrs": "N",
+        "main_fuel_type": 26,
+        "boiler_flue_type": 2,
+        "fan_flue_present": "Y",
+        "heat_emitter_type": 1,
+        "emitter_temperature": 0,
+        "main_heating_number": 1,
+        "main_heating_control": 2106,
+        "main_heating_category": 2,
+        "main_heating_fraction": 1,
+        "central_heating_pump_age": 0,
+        "main_heating_data_source": 1,
+        "main_heating_index_number": 15709
+      }
+    ],
+    "immersion_heating_type": "NA",
+    "secondary_heating_type": 691,
+    "has_fixed_air_conditioning": "false"
+  },
+  "sap_version": 10.2,
+  "sap_windows": [
+    {
+      "pvc_frame": "true",
+      "orientation": 1,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 0.48,
+      "window_height": 0.92,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 1,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 0.57,
+      "window_height": 1.12,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 1,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 1.44,
+      "window_height": 1.21,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 2,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 0.54,
+      "window_height": 1.11,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 8,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 0.48,
+      "window_height": 0.92,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 1,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 0.61,
+      "window_height": 1.05,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 1,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 1,
+      "window_height": 1.24,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 1,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 1.83,
+      "window_height": 1.07,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 7,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 0.56,
+      "window_height": 1.13,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 5,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 1.02,
+      "window_height": 1.17,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 5,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 1.93,
+      "window_height": 1.21,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 5,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 1.81,
+      "window_height": 1.29,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 4,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 0.54,
+      "window_height": 1.32,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 6,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 1.93,
+      "window_height": 1.21,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 5,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 1.93,
+      "window_height": 1.13,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 5,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 0.99,
+      "window_height": 1.05,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 5,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 2,
+      "window_height": 1.21,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    }
+  ],
+  "schema_type": "RdSAP-Schema-21.0.1",
+  "uprn_source": "Energy Assessor",
+  "country_code": "ENG",
+  "main_heating": [
+    {
+      "description": "Boiler and radiators, mains gas",
+      "energy_efficiency_rating": 4,
+      "environmental_efficiency_rating": 4
+    }
+  ],
+  "air_tightness": {
+    "description": "(not tested)",
+    "energy_efficiency_rating": 0,
+    "environmental_efficiency_rating": 0
+  },
+  "dwelling_type": "Semi-detached house",
+  "language_code": 1,
+  "pressure_test": 4,
+  "property_type": 0,
+  "address_line_1": "49 Cotefield Road",
+  "assessment_type": "RdSAP",
+  "completion_date": "2026-06-03",
+  "inspection_date": "2026-06-03",
+  "extensions_count": 0,
+  "measurement_type": 1,
+  "total_floor_area": 107,
+  "transaction_type": 5,
+  "conservatory_type": 1,
+  "heated_room_count": 6,
+  "registration_date": "2026-06-03",
+  "sap_energy_source": {
+    "mains_gas": "Y",
+    "meter_type": 2,
+    "pv_connection": 0,
+    "photovoltaic_supply": {
+      "none_or_no_details": {
+        "percent_roof_area": 0
+      }
+    },
+    "wind_turbines_count": 0,
+    "gas_smart_meter_present": "false",
+    "is_dwelling_export_capable": "false",
+    "wind_turbines_terrain_type": 2,
+    "electricity_smart_meter_present": "false"
+  },
+  "secondary_heating": {
+    "description": "Room heaters, electric",
+    "energy_efficiency_rating": 0,
+    "environmental_efficiency_rating": 0
+  },
+  "extract_fans_count": 2,
+  "sap_building_parts": [
+    {
+      "identifier": "Main Dwelling",
+      "wall_dry_lined": "N",
+      "wall_thickness": 300,
+      "floor_heat_loss": 7,
+      "roof_construction": 4,
+      "wall_construction": 4,
+      "building_part_number": 1,
+      "sap_floor_dimensions": [
+        {
+          "floor": 0,
+          "room_height": {
+            "value": 2.4,
+            "quantity": "metres"
+          },
+          "floor_insulation": 1,
+          "total_floor_area": {
+            "value": 53.63,
+            "quantity": "square metres"
+          },
+          "party_wall_length": {
+            "value": 5.63,
+            "quantity": "metres"
+          },
+          "floor_construction": 1,
+          "heat_loss_perimeter": {
+            "value": 26.13,
+            "quantity": "metres"
+          }
+        },
+        {
+          "floor": 1,
+          "room_height": {
+            "value": 2.45,
+            "quantity": "metres"
+          },
+          "total_floor_area": {
+            "value": 53.63,
+            "quantity": "square metres"
+          },
+          "party_wall_length": {
+            "value": 5.63,
+            "quantity": "metres"
+          },
+          "heat_loss_perimeter": {
+            "value": 21.78,
+            "quantity": "metres"
+          }
+        }
+      ],
+      "wall_insulation_type": 2,
+      "construction_age_band": "D",
+      "party_wall_construction": 0,
+      "wall_thickness_measured": "Y",
+      "roof_insulation_location": 2,
+      "roof_insulation_thickness": "300mm",
+      "wall_insulation_thickness": "NI",
+      "floor_insulation_thickness": "NI"
+    }
+  ],
+  "solar_water_heating": "N",
+  "habitable_room_count": 6,
+  "heating_cost_current": {
+    "value": 1131,
+    "currency": "GBP"
+  },
+  "insulated_door_count": 0,
+  "co2_emissions_current": 2.9,
+  "energy_rating_average": 60,
+  "energy_rating_current": 70,
+  "lighting_cost_current": {
+    "value": 63,
+    "currency": "GBP"
+  },
+  "main_heating_controls": [
+    {
+      "description": "Programmer, room thermostat and TRVs",
+      "energy_efficiency_rating": 4,
+      "environmental_efficiency_rating": 4
+    }
+  ],
+  "has_hot_water_cylinder": "false",
+  "heating_cost_potential": {
+    "value": 1031,
+    "currency": "GBP"
+  },
+  "hot_water_cost_current": {
+    "value": 218,
+    "currency": "GBP"
+  },
+  "mechanical_ventilation": 0,
+  "percent_draughtproofed": 100,
+  "suggested_improvements": [
+    {
+      "sequence": 1,
+      "typical_saving": {
+        "value": 100,
+        "currency": "GBP"
+      },
+      "indicative_cost": "\u00a35,000 - \u00a310,000",
+      "improvement_type": "W2",
+      "improvement_details": {
+        "improvement_number": 58
+      },
+      "improvement_category": 5,
+      "energy_performance_rating": 72,
+      "environmental_impact_rating": 75
+    },
+    {
+      "sequence": 2,
+      "typical_saving": {
+        "value": 223,
+        "currency": "GBP"
+      },
+      "indicative_cost": "\u00a38,000 - \u00a310,000",
+      "improvement_type": "U",
+      "improvement_details": {
+        "improvement_number": 34
+      },
+      "improvement_category": 5,
+      "energy_performance_rating": 76,
+      "environmental_impact_rating": 76
+    }
+  ],
+  "co2_emissions_potential": 2.5,
+  "energy_rating_potential": 76,
+  "lighting_cost_potential": {
+    "value": 63,
+    "currency": "GBP"
+  },
+  "schema_version_original": "21.0.1",
+  "hot_water_cost_potential": {
+    "value": 218,
+    "currency": "GBP"
+  },
+  "renewable_heat_incentive": {
+    "water_heating": 2512.47,
+    "space_heating_existing_dwelling": 9580.15
+  },
+  "draughtproofed_door_count": 2,
+  "energy_consumption_current": 154,
+  "has_fixed_air_conditioning": "false",
+  "multiple_glazed_proportion": 100,
+  "calculation_software_version": "5.02r0344",
+  "energy_consumption_potential": 130,
+  "environmental_impact_current": 73,
+  "current_energy_efficiency_band": "C",
+  "environmental_impact_potential": 76,
+  "has_heated_separate_conservatory": "false",
+  "potential_energy_efficiency_band": "C",
+  "co2_emissions_current_per_floor_area": 27,
+  "low_energy_fixed_lighting_bulbs_count": 14,
+  "incandescent_fixed_lighting_bulbs_count": 0
+}

tests/domain/sap10_calculator/rdsap/fixtures/golden/5500-5070-0822-0201-3663.json

@@ -0,0 +1,523 @@
+{
+  "uprn": 77079925,
+  "roofs": [
+    {
+      "description": "Pitched, 100 mm loft insulation",
+      "energy_efficiency_rating": 3,
+      "environmental_efficiency_rating": 3
+    },
+    {
+      "description": "Pitched, insulated (assumed)",
+      "energy_efficiency_rating": 3,
+      "environmental_efficiency_rating": 3
+    }
+  ],
+  "walls": [
+    {
+      "description": "Cavity wall, filled cavity",
+      "energy_efficiency_rating": 4,
+      "environmental_efficiency_rating": 4
+    }
+  ],
+  "floors": [
+    {
+      "description": "Suspended, no insulation (assumed)",
+      "energy_efficiency_rating": 0,
+      "environmental_efficiency_rating": 0
+    }
+  ],
+  "status": "entered",
+  "tenure": 2,
+  "window": {
+    "description": "Fully double glazed",
+    "energy_efficiency_rating": 3,
+    "environmental_efficiency_rating": 3
+  },
+  "lighting": {
+    "description": "Good lighting efficiency",
+    "energy_efficiency_rating": 4,
+    "environmental_efficiency_rating": 4
+  },
+  "postcode": "M22 4FA",
+  "hot_water": {
+    "description": "From main system",
+    "energy_efficiency_rating": 4,
+    "environmental_efficiency_rating": 4
+  },
+  "post_town": "MANCHESTER",
+  "built_form": 2,
+  "created_at": "2026-06-03 10:48:51",
+  "door_count": 2,
+  "region_code": 19,
+  "report_type": 2,
+  "sap_heating": {
+    "number_baths": 1,
+    "cylinder_size": 1,
+    "shower_outlets": [
+      {
+        "shower_wwhrs": 1,
+        "shower_outlet_type": 2
+      }
+    ],
+    "number_baths_wwhrs": 0,
+    "water_heating_code": 901,
+    "water_heating_fuel": 26,
+    "secondary_fuel_type": 29,
+    "main_heating_details": [
+      {
+        "has_fghrs": "N",
+        "main_fuel_type": 26,
+        "boiler_flue_type": 2,
+        "fan_flue_present": "Y",
+        "heat_emitter_type": 1,
+        "emitter_temperature": 0,
+        "main_heating_number": 1,
+        "main_heating_control": 2106,
+        "main_heating_category": 2,
+        "main_heating_fraction": 1,
+        "central_heating_pump_age": 0,
+        "main_heating_data_source": 1,
+        "main_heating_index_number": 17741
+      }
+    ],
+    "immersion_heating_type": "NA",
+    "secondary_heating_type": 691,
+    "has_fixed_air_conditioning": "false"
+  },
+  "sap_version": 10.2,
+  "sap_windows": [
+    {
+      "pvc_frame": "true",
+      "orientation": 6,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 0.98,
+      "window_height": 0.93,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 6,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 0.4,
+      "window_height": 0.74,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 6,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 1.49,
+      "window_height": 1.99,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 6,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 1.13,
+      "window_height": 1.06,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 6,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 0.17,
+      "window_height": 0.75,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 6,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 0.92,
+      "window_height": 0.94,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 8,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 1.01,
+      "window_height": 1.21,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 8,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 0.41,
+      "window_height": 0.85,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 2,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 1.03,
+      "window_height": 1.26,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 2,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 1.12,
+      "window_height": 0.92,
+      "draught_proofed": "true",
+      "window_location": 0,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 2,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 1.63,
+      "window_height": 0.98,
+      "draught_proofed": "true",
+      "window_location": 1,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 2,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 2.64,
+      "window_height": 1.2,
+      "draught_proofed": "true",
+      "window_location": 1,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    },
+    {
+      "pvc_frame": "true",
+      "orientation": 2,
+      "window_type": 1,
+      "glazing_type": 2,
+      "window_width": 0.55,
+      "window_height": 1.22,
+      "draught_proofed": "true",
+      "window_location": 1,
+      "window_wall_type": 1,
+      "permanent_shutters_present": "N",
+      "permanent_shutters_insulated": "N"
+    }
+  ],
+  "schema_type": "RdSAP-Schema-21.0.1",
+  "uprn_source": "Energy Assessor",
+  "country_code": "ENG",
+  "main_heating": [
+    {
+      "description": "Boiler and radiators, mains gas",
+      "energy_efficiency_rating": 4,
+      "environmental_efficiency_rating": 4
+    }
+  ],
+  "air_tightness": {
+    "description": "(not tested)",
+    "energy_efficiency_rating": 0,
+    "environmental_efficiency_rating": 0
+  },
+  "dwelling_type": "Semi-detached house",
+  "language_code": 1,
+  "pressure_test": 4,
+  "property_type": 0,
+  "address_line_1": "75 Kenworthy Lane",
+  "assessment_type": "RdSAP",
+  "completion_date": "2026-06-03",
+  "inspection_date": "2026-06-03",
+  "extensions_count": 1,
+  "measurement_type": 1,
+  "total_floor_area": 83,
+  "transaction_type": 5,
+  "conservatory_type": 1,
+  "heated_room_count": 5,
+  "registration_date": "2026-06-03",
+  "sap_energy_source": {
+    "mains_gas": "Y",
+    "meter_type": 2,
+    "pv_connection": 0,
+    "photovoltaic_supply": {
+      "none_or_no_details": {
+        "percent_roof_area": 0
+      }
+    },
+    "wind_turbines_count": 0,
+    "gas_smart_meter_present": "false",
+    "is_dwelling_export_capable": "false",
+    "wind_turbines_terrain_type": 2,
+    "electricity_smart_meter_present": "false"
+  },
+  "secondary_heating": {
+    "description": "Room heaters, electric",
+    "energy_efficiency_rating": 0,
+    "environmental_efficiency_rating": 0
+  },
+  "extract_fans_count": 2,
+  "sap_building_parts": [
+    {
+      "identifier": "Main Dwelling",
+      "wall_dry_lined": "N",
+      "wall_thickness": 300,
+      "floor_heat_loss": 7,
+      "roof_construction": 4,
+      "wall_construction": 4,
+      "building_part_number": 1,
+      "sap_floor_dimensions": [
+        {
+          "floor": 0,
+          "room_height": {
+            "value": 2.43,
+            "quantity": "metres"
+          },
+          "floor_insulation": 1,
+          "total_floor_area": {
+            "value": 35.07,
+            "quantity": "square metres"
+          },
+          "party_wall_length": {
+            "value": 4.29,
+            "quantity": "metres"
+          },
+          "floor_construction": 2,
+          "heat_loss_perimeter": {
+            "value": 11.12,
+            "quantity": "metres"
+          }
+        },
+        {
+          "floor": 1,
+          "room_height": {
+            "value": 2.45,
+            "quantity": "metres"
+          },
+          "total_floor_area": {
+            "value": 35.67,
+            "quantity": "square metres"
+          },
+          "party_wall_length": {
+            "value": 4.84,
+            "quantity": "metres"
+          },
+          "heat_loss_perimeter": {
+            "value": 12.21,
+            "quantity": "metres"
+          }
+        }
+      ],
+      "wall_insulation_type": 2,
+      "construction_age_band": "C",
+      "party_wall_construction": 0,
+      "wall_thickness_measured": "Y",
+      "roof_insulation_location": 2,
+      "roof_insulation_thickness": "100mm",
+      "wall_insulation_thickness": "NI",
+      "floor_insulation_thickness": "NI"
+    },
+    {
+      "identifier": "Extension 1",
+      "wall_dry_lined": "N",
+      "wall_thickness": 300,
+      "floor_heat_loss": 7,
+      "roof_construction": 5,
+      "wall_construction": 4,
+      "building_part_number": 2,
+      "sap_floor_dimensions": [
+        {
+          "floor": 0,
+          "room_height": {
+            "value": 2.43,
+            "quantity": "metres"
+          },
+          "floor_insulation": 1,
+          "total_floor_area": {
+            "value": 6.07,
+            "quantity": "square metres"
+          },
+          "party_wall_length": {
+            "value": 1.2,
+            "quantity": "metres"
+          },
+          "floor_construction": 2,
+          "heat_loss_perimeter": {
+            "value": 6.26,
+            "quantity": "metres"
+          }
+        },
+        {
+          "floor": 1,
+          "room_height": {
+            "value": 2.45,
+            "quantity": "metres"
+          },
+          "total_floor_area": {
+            "value": 6.07,
+            "quantity": "square metres"
+          },
+          "party_wall_length": {
+            "value": 1.2,
+            "quantity": "metres"
+          },
+          "heat_loss_perimeter": {
+            "value": 6.26,
+            "quantity": "metres"
+          }
+        }
+      ],
+      "wall_insulation_type": 2,
+      "construction_age_band": "C",
+      "party_wall_construction": 0,
+      "wall_thickness_measured": "Y",
+      "roof_insulation_location": 4,
+      "roof_insulation_thickness": "ND",
+      "wall_insulation_thickness": "NI",
+      "floor_insulation_thickness": "NI"
+    }
+  ],
+  "solar_water_heating": "N",
+  "habitable_room_count": 5,
+  "heating_cost_current": {
+    "value": 1013,
+    "currency": "GBP"
+  },
+  "insulated_door_count": 0,
+  "co2_emissions_current": 2.4,
+  "energy_rating_average": 60,
+  "energy_rating_current": 66,
+  "lighting_cost_current": {
+    "value": 53,
+    "currency": "GBP"
+  },
+  "main_heating_controls": [
+    {
+      "description": "Programmer, room thermostat and TRVs",
+      "energy_efficiency_rating": 4,
+      "environmental_efficiency_rating": 4
+    }
+  ],
+  "has_hot_water_cylinder": "false",
+  "heating_cost_potential": {
+    "value": 926,
+    "currency": "GBP"
+  },
+  "hot_water_cost_current": {
+    "value": 292,
+    "currency": "GBP"
+  },
+  "mechanical_ventilation": 0,
+  "percent_draughtproofed": 100,
+  "suggested_improvements": [
+    {
+      "sequence": 1,
+      "typical_saving": {
+        "value": 87,
+        "currency": "GBP"
+      },
+      "indicative_cost": "\u00a35,000 - \u00a310,000",
+      "improvement_type": "W1",
+      "improvement_details": {
+        "improvement_number": 57
+      },
+      "improvement_category": 5,
+      "energy_performance_rating": 68,
+      "environmental_impact_rating": 75
+    },
+    {
+      "sequence": 2,
+      "typical_saving": {
+        "value": 224,
+        "currency": "GBP"
+      },
+      "indicative_cost": "\u00a38,000 - \u00a310,000",
+      "improvement_type": "U",
+      "improvement_details": {
+        "improvement_number": 34
+      },
+      "improvement_category": 5,
+      "energy_performance_rating": 73,
+      "environmental_impact_rating": 76
+    }
+  ],
+  "co2_emissions_potential": 2.1,
+  "energy_rating_potential": 73,
+  "lighting_cost_potential": {
+    "value": 53,
+    "currency": "GBP"
+  },
+  "schema_version_original": "21.0.1",
+  "hot_water_cost_potential": {
+    "value": 292,
+    "currency": "GBP"
+  },
+  "renewable_heat_incentive": {
+    "water_heating": 2105.06,
+    "space_heating_existing_dwelling": 8424.88
+  },
+  "draughtproofed_door_count": 2,
+  "energy_consumption_current": 174,
+  "has_fixed_air_conditioning": "false",
+  "multiple_glazed_proportion": 100,
+  "calculation_software_version": "5.02r0344",
+  "energy_consumption_potential": 146,
+  "environmental_impact_current": 73,
+  "current_energy_efficiency_band": "D",
+  "environmental_impact_potential": 76,
+  "has_heated_separate_conservatory": "false",
+  "potential_energy_efficiency_band": "C",
+  "co2_emissions_current_per_floor_area": 29,
+  "low_energy_fixed_lighting_bulbs_count": 9,
+  "incandescent_fixed_lighting_bulbs_count": 0
+}

tests/domain/sap10_calculator/rdsap/test_cert_to_inputs.py

@@ -14,10 +14,18 @@ area fraction); SAP 10.3 specification (13-01-2026) Tables 4a/4e/12.
 
 from __future__ import annotations
 
-from typing import Final
+from typing import Final, Optional
 
 import pytest
 
+from datatypes.epc.domain.mapper import (
+    _map_elmhurst_room_in_roof,  # pyright: ignore[reportPrivateUsage]
+)
+from datatypes.epc.surveys.elmhurst_site_notes import (
+    RoomInRoof as ElmhurstRoomInRoof,
+    RoomInRoofSurface as ElmhurstRoomInRoofSurface,
+)
+
 from datatypes.epc.domain.epc_property_data import (
     EpcPropertyData,
     MainHeatingDetail,
@@ -44,16 +52,24 @@ from domain.sap10_calculator.rdsap.cert_to_inputs import (
     _heat_network_code_302_effective_factor,  # pyright: ignore[reportPrivateUsage]
     _heat_network_distribution_electricity,  # pyright: ignore[reportPrivateUsage]
     _heat_network_dlf,  # pyright: ignore[reportPrivateUsage]
+    _heat_network_factor_fuel_code,  # pyright: ignore[reportPrivateUsage]
+    _heat_network_standing_charge_gbp,  # pyright: ignore[reportPrivateUsage]
     _is_electric_main,  # pyright: ignore[reportPrivateUsage]
     _is_heat_network_electric_main,  # pyright: ignore[reportPrivateUsage]
     _is_electric_water,  # pyright: ignore[reportPrivateUsage]
     _is_off_peak_meter,  # pyright: ignore[reportPrivateUsage]
     _main_floor_u_value,  # pyright: ignore[reportPrivateUsage]
+    _main_space_heating_high_rate_fraction,  # pyright: ignore[reportPrivateUsage]
     _other_fuel_cost_gbp_per_kwh,  # pyright: ignore[reportPrivateUsage]
+    _pv_diverter_monthly_kwh,  # pyright: ignore[reportPrivateUsage]
+    _pv_dwelling_import_price_gbp_per_kwh,  # pyright: ignore[reportPrivateUsage]
+    _pv_eligible_demand_monthly_kwh,  # pyright: ignore[reportPrivateUsage]
+    _primary_loss_applies,  # pyright: ignore[reportPrivateUsage]
     _rdsap_extract_fans_default,  # pyright: ignore[reportPrivateUsage]
     _pv_overshading_factor,  # pyright: ignore[reportPrivateUsage]
     _pv_pitch_deg,  # pyright: ignore[reportPrivateUsage]
     _responsiveness,  # pyright: ignore[reportPrivateUsage]
+    _secondary_fuel_cost_gbp_per_kwh,  # pyright: ignore[reportPrivateUsage]
     _secondary_heating_fraction_for_category,  # pyright: ignore[reportPrivateUsage]
     _section_12_4_4_summer_immersion_applies,  # pyright: ignore[reportPrivateUsage]
     _separately_timed_dhw,  # pyright: ignore[reportPrivateUsage]
@@ -1754,6 +1770,209 @@ def test_other_fuel_cost_for_18_hour_tariff_uses_18_hour_high_rate() -> None:
     )
 
 
+def test_main_space_high_rate_fraction_zero_for_off_peak_storage_heaters() -> None:
+    # Arrange — SAP 10.2 Appendix M1 §3a (PDF p.93): E_space,m (211) is
+    # included in D_PV "only where the fuel code applied to it in Section
+    # 10a is 30, 32, 34, 35 or 38 (i.e. electricity not at the low-rate)".
+    # Electric STORAGE heaters (code 402) on a 7-hour off-peak tariff are
+    # charged wholly at the low rate (Table 12a Grid 1 SH fraction 0.00 /
+    # `_table_12a_system_for_main` → None) — worksheet (240) high-rate
+    # cost = 0 — so none of (211) may enter D_PV.
+    from domain.sap10_calculator.tables.table_12a import Tariff
+
+    storage_main = MainHeatingDetail(
+        has_fghrs=False,
+        main_fuel_type=29,  # electricity
+        heat_emitter_type=1,
+        emitter_temperature=1,
+        main_heating_control=2402,
+        main_heating_category=7,
+        sap_main_heating_code=402,
+    )
+
+    # Act
+    off_peak = _main_space_heating_high_rate_fraction(
+        storage_main, Tariff.SEVEN_HOUR
+    )
+    standard = _main_space_heating_high_rate_fraction(
+        storage_main, Tariff.STANDARD
+    )
+    gas = _main_space_heating_high_rate_fraction(
+        _gas_boiler_detail(sap_main_heating_code=102), Tariff.SEVEN_HOUR
+    )
+
+    # Assert
+    assert abs(off_peak - 0.0) <= 1e-9
+    # STANDARD tariff has no high/low split → 100% high rate.
+    assert abs(standard - 1.0) <= 1e-9
+    # Non-electric main never carries an off-peak split.
+    assert abs(gas - 1.0) <= 1e-9
+
+
+def test_pv_eligible_demand_excludes_low_rate_main_space_heating() -> None:
+    # Arrange — SAP 10.2 Appendix M1 §3a (PDF p.93). A main billed wholly
+    # at the low rate (high-rate fraction 0.0) must contribute zero to
+    # D_PV even though its Table-12 code (30) is in the eligible set; the
+    # secondary (also code 30) at its full high-rate fraction stays in.
+    main_1 = tuple(float(100 + m) for m in range(12))
+    secondary = tuple(float(10 + m) for m in range(12))
+    base = tuple(float(5) for _ in range(12))  # lighting et al.
+
+    # Act
+    excluded = _pv_eligible_demand_monthly_kwh(
+        lighting_monthly_kwh=base,
+        appliances_monthly_kwh=(0.0,) * 12,
+        cooking_monthly_kwh=(0.0,) * 12,
+        electric_shower_monthly_kwh=(0.0,) * 12,
+        pumps_fans_monthly_kwh=(0.0,) * 12,
+        main_1_fuel_monthly_kwh=main_1,
+        secondary_fuel_monthly_kwh=secondary,
+        hot_water_monthly_kwh=(0.0,) * 12,
+        main_fuel_code_table_12=30,
+        secondary_fuel_code_table_12=30,
+        water_heating_fuel_code_table_12=26,  # gas → no E_water
+        main_space_high_rate_fraction=0.0,
+    )
+    included = _pv_eligible_demand_monthly_kwh(
+        lighting_monthly_kwh=base,
+        appliances_monthly_kwh=(0.0,) * 12,
+        cooking_monthly_kwh=(0.0,) * 12,
+        electric_shower_monthly_kwh=(0.0,) * 12,
+        pumps_fans_monthly_kwh=(0.0,) * 12,
+        main_1_fuel_monthly_kwh=main_1,
+        secondary_fuel_monthly_kwh=secondary,
+        hot_water_monthly_kwh=(0.0,) * 12,
+        main_fuel_code_table_12=30,
+        secondary_fuel_code_table_12=30,
+        water_heating_fuel_code_table_12=26,
+        main_space_high_rate_fraction=1.0,
+    )
+
+    # Assert — excluded drops the full (211); secondary stays in both.
+    for m in range(12):
+        assert abs(excluded[m] - (base[m] + secondary[m])) <= 1e-9
+        assert abs(included[m] - (base[m] + secondary[m] + main_1[m])) <= 1e-9
+
+
+def test_pv_dwelling_import_price_blends_high_low_on_off_peak() -> None:
+    # Arrange — SAP 10.2 Appendix M1 §6 (PDF p.94, lines 5510-5513): PV
+    # used in the dwelling is credited at "a weighted average of high and
+    # low rates (Table 12a)". On a 7-hour tariff the ALL_OTHER_USES blend
+    # is 0.90 × 15.29 + 0.10 × 5.50 = 14.311 p/kWh (worksheet case 19
+    # (252) "PV used in dwelling" = 14.3110). STANDARD tariff has no
+    # split → flat Table 32 code 30 = 13.19 p/kWh (unchanged).
+    from domain.sap10_calculator.tables.table_12a import Tariff
+
+    # Act
+    off_peak = _pv_dwelling_import_price_gbp_per_kwh(
+        Tariff.SEVEN_HOUR, SAP_10_2_SPEC_PRICES
+    )
+    standard = _pv_dwelling_import_price_gbp_per_kwh(
+        Tariff.STANDARD, SAP_10_2_SPEC_PRICES
+    )
+
+    # Assert
+    assert abs(off_peak - 0.14311) <= 1e-6
+    assert abs(standard - 0.1319) <= 1e-6
+
+
+def _pv_diverter_epc():
+    """A minimal dwelling that satisfies every Appendix G4 inclusion
+    condition: a 210 L cylinder (code 4), no solar HW, no battery, with
+    `pv_diverter_present` set on the energy source."""
+    from dataclasses import replace
+
+    epc = make_minimal_sap10_epc(
+        total_floor_area_m2=90.0,
+        habitable_rooms_count=4,
+        country_code="ENG",
+        has_hot_water_cylinder=True,
+        solar_water_heating=False,
+        sap_heating=make_sap_heating(
+            main_heating_details=[_gas_boiler_detail(sap_main_heating_code=102)],
+            cylinder_size=4,  # RdSAP Table 28 code 4 → 210 L
+        ),
+    )
+    return replace(
+        epc,
+        sap_energy_source=replace(
+            epc.sap_energy_source, pv_diverter_present=True
+        ),
+    )
+
+
+def test_pv_diverter_monthly_applies_g4_correction_and_clamp() -> None:
+    # Arrange — SAP 10.2 Appendix G4 step 4 (PDF p.73): SPV,diverter,m =
+    # EPV,m(1 − βm) × 0.8 × 0.9, clamped to ≤ (62)m + (63a)m. With a
+    # 100-kWh monthly surplus the uncapped diverter input is 72 kWh; a
+    # month whose water demand is only 50 kWh clamps it to 50.
+    epc = _pv_diverter_epc()
+    export = tuple(100.0 for _ in range(12))
+    demand = tuple(50.0 if m < 6 else 1000.0 for m in range(12))
+
+    # Act
+    out = _pv_diverter_monthly_kwh(
+        epc=epc,
+        pv_export_monthly_kwh=export,
+        water_demand_monthly_kwh=demand,
+        avg_daily_hot_water_l=120.0,  # < 210 L cylinder
+        battery_capacity_kwh=0.0,
+        pv_generation_kwh=1200.0,
+    )
+
+    # Assert
+    assert out is not None
+    for m in range(12):
+        expected = min(100.0 * 0.8 * 0.9, demand[m])
+        assert abs(out[m] - expected) <= 1e-9
+
+
+def test_pv_diverter_disregarded_when_any_g4_condition_fails() -> None:
+    # Arrange — SAP 10.2 Appendix G4 step 1: if a PV system / large-enough
+    # cylinder / no-solar-HW / no-battery condition is not met, software
+    # disregards the diverter (returns None).
+    from dataclasses import replace
+
+    epc = _pv_diverter_epc()
+    export: tuple[float, ...] = (100.0,) * 12
+    demand: tuple[float, ...] = (1000.0,) * 12
+
+    def divert(
+        e: object, avg_l: float = 120.0, battery: float = 0.0, pv_gen: float = 1200.0
+    ) -> Optional[tuple[float, ...]]:
+        return _pv_diverter_monthly_kwh(
+            epc=e,  # pyright: ignore[reportArgumentType]
+            pv_export_monthly_kwh=export,
+            water_demand_monthly_kwh=demand,
+            avg_daily_hot_water_l=avg_l,
+            battery_capacity_kwh=battery,
+            pv_generation_kwh=pv_gen,
+        )
+
+    # Act / Assert — sanity: all conditions met → not None.
+    assert divert(epc) is not None
+    # Diverter not present.
+    assert (
+        divert(
+            replace(
+                epc,
+                sap_energy_source=replace(
+                    epc.sap_energy_source, pv_diverter_present=False
+                ),
+            )
+        )
+        is None
+    )
+    # No PV generation (condition a).
+    assert divert(epc, pv_gen=0.0) is None
+    # Cylinder not larger than (43) average daily HW use (condition b).
+    assert divert(epc, avg_l=9999.0) is None
+    # Battery present (condition d).
+    assert divert(epc, battery=5.0) is None
+    # Solar water heating present (condition c).
+    assert divert(replace(epc, solar_water_heating=True)) is None
+
+
 def test_is_off_peak_meter_recognises_bare_18_hour_lodging() -> None:
     # Arrange — RdSAP 10 §17 page 85 row 10-2 lodges 18-hour meter
     # as the bare "18-hour" or "18 Hour" form (Elmhurst Summary §14.2
@@ -1854,6 +2073,137 @@ def test_separately_timed_dhw_excludes_electric_immersion_per_table_2b_note_b()
     assert sep_immersion is False
 
 
+def test_separately_timed_dhw_excludes_dedicated_water_heater_per_table_2b_note_b() -> None:
+    # Arrange — SAP 10.2 Table 2b note b) (PDF p.159) applies the ×0.9
+    # temperature-factor reduction only when DHW "is separately timed"
+    # relative to space heating on a SHARED heat generator ("boiler
+    # systems, warm air systems and heat pump systems"). Per RdSAP 10
+    # §10.5.1 (PDF p.55) a separate boiler/circulator providing DHW only
+    # (water-heating code 911 = "Gas boiler/circulator for water heating
+    # only") is NOT the main space-heating system — here space is by
+    # electric storage heaters (SAP code 402). With no shared generator
+    # there is no separate DHW timer to apply the ×0.9 against, so the
+    # multiplier must not fire — the same principle as the WHC 903
+    # electric-immersion carve-out above. Simulated case 19's worksheet
+    # confirms it: cylinder thermostat present + "Separate Time Control:
+    # No" → (53) Temperature factor 0.6000 (base, not 0.54 = 0.6 × 0.9)
+    # AND (59)m primary loss h=5 (winter Jan 64.5792), not h=3 (43.31).
+    storage_heater_main = MainHeatingDetail(
+        has_fghrs=False,
+        main_fuel_type=30,  # electricity
+        heat_emitter_type="",
+        emitter_temperature=1,
+        main_heating_control=2402,  # storage-heater auto-charge control
+        main_heating_category=None,
+        sap_main_heating_code=402,  # electric storage heaters
+    )
+    dedicated_gas_water_heater_epc = make_minimal_sap10_epc(
+        total_floor_area_m2=_TYPICAL_TFA_M2,
+        habitable_rooms_count=4,
+        country_code="ENG",
+        has_hot_water_cylinder=True,
+        sap_heating=make_sap_heating(
+            main_heating_details=[storage_heater_main],
+            water_heating_fuel=26,  # mains gas (dedicated WHS boiler)
+            water_heating_code=911,  # gas boiler/circulator, water only
+            cylinder_size=4,
+            cylinder_insulation_type=2,  # loose jacket
+            cylinder_insulation_thickness_mm=50,
+        ),
+    )
+
+    # Act
+    separately_timed = _separately_timed_dhw(
+        dedicated_gas_water_heater_epc, storage_heater_main,
+    )
+
+    # Assert — dedicated water-heating-only system → not separately timed.
+    assert separately_timed is False
+
+
+def test_secondary_electric_off_peak_bills_at_table_12a_direct_acting_high_rate() -> None:
+    # Arrange — SAP 10.2 Table 12a Grid 1 (PDF p.191): secondary heating
+    # is a direct-acting electric room heater (RdSAP 10 §A.2.2 default),
+    # which sits on the "Other systems including direct-acting electric"
+    # row. For a 7-hour (Economy-7) tariff that row's high-rate fraction
+    # is 1.00 — ALL secondary consumption bills at the high rate, NOT the
+    # off-peak low rate that storage-heater charging earns. Simulated
+    # case 19's worksheet (242) is the evidence: "Space heating -
+    # secondary (1.00*15.29 + 0.00*5.50)" → 15.29 p/kWh = £0.1529. Pre-
+    # slice `_secondary_fuel_cost_gbp_per_kwh` returned the 7-hour low
+    # rate 5.50 p (£0.0550) for every off-peak electric secondary,
+    # under-charging by 9.79 p/kWh × the secondary kWh (~£340 on case 19).
+    storage_heater_main = MainHeatingDetail(
+        has_fghrs=False,
+        main_fuel_type=30,  # electricity
+        heat_emitter_type="",
+        emitter_temperature=1,
+        main_heating_control=2402,
+        main_heating_category=None,
+        sap_main_heating_code=402,  # electric storage heaters
+    )
+    dual_meter_off_peak_epc = make_minimal_sap10_epc(
+        total_floor_area_m2=_TYPICAL_TFA_M2,
+        habitable_rooms_count=4,
+        country_code="ENG",
+        sap_heating=make_sap_heating(
+            main_heating_details=[storage_heater_main],
+            # secondary_fuel_type omitted → §A.2.2 portable electric default
+        ),
+    )
+
+    # Act
+    secondary_rate_gbp_per_kwh = _secondary_fuel_cost_gbp_per_kwh(
+        dual_meter_off_peak_epc.sap_heating,
+        storage_heater_main,
+        1,  # Dual meter → 7-hour off-peak tariff
+        SAP_10_2_SPEC_PRICES,
+    )
+
+    # Assert — 1.00 × 15.29 p + 0.00 × 5.50 p = 15.29 p/kWh = £0.1529.
+    assert abs(secondary_rate_gbp_per_kwh - 0.1529) <= 1e-6
+
+
+def test_sap_table_3_primary_loss_applies_to_dedicated_water_heating_boiler_circulator() -> None:
+    # Arrange — SAP 10.2 Table 3 (PDF p.160) row 1: primary circuit loss
+    # applies when "hot water is heated by a heat generator (e.g. boiler)
+    # connected to a hot water storage vessel via insulated or
+    # uninsulated pipes". The dedicated "boiler/circulator for water
+    # heating only" water-heating codes (Table 4a hot-water section, PDF
+    # p.166): 911 gas, 912 liquid fuel, 913 solid fuel, 921-931 range
+    # cooker with boiler — each is a boiler feeding the cylinder through a
+    # primary loop, so the loss applies regardless of what the SPACE
+    # heating system is. Simulated case 19 pairs electric storage heaters
+    # (SAP code 402) for space with a WHS 911 gas boiler/circulator for
+    # water: `_water_heating_main` resolves to the code-402 storage main
+    # (electric, no primary loop), so before this slice every dedicated-
+    # boiler branch missed the cylinder's primary circuit and (59)m went
+    # to zero — dropping the worksheet's 676.68 kWh/yr (59) and inflating
+    # HW fuel (219).
+    storage_heater_main = MainHeatingDetail(
+        has_fghrs=False,
+        main_fuel_type=30,  # electricity
+        heat_emitter_type="",
+        emitter_temperature=1,
+        main_heating_control=2402,
+        main_heating_category=None,
+        sap_main_heating_code=402,  # electric storage heaters (space)
+    )
+
+    # Act
+    applies_with_cylinder = _primary_loss_applies(
+        storage_heater_main, True, None, water_heating_code=911,
+    )
+    applies_without_cylinder = _primary_loss_applies(
+        storage_heater_main, False, None, water_heating_code=911,
+    )
+
+    # Assert — WHS 911 + cylinder → primary loss applies; no cylinder →
+    # no primary circuit, no loss.
+    assert applies_with_cylinder is True
+    assert applies_without_cylinder is False
+
+
 def test_water_efficiency_uses_table_4a_water_column_for_heat_pumps_per_sap_10_2() -> None:
     # Arrange — SAP 10.2 Table 4a (PDF p.163-164) gives heat pumps two
     # efficiency columns: "space" and "water". For low-temperature
@@ -2120,6 +2470,70 @@ def test_elmhurst_main_fuel_to_sap10_maps_bio_liquid_water_heating_labels() -> N
     assert _ELMHURST_MAIN_FUEL_TO_SAP10["Bio-liquid HVO from used cooking oil"] == 71
 
 
+def _placeholder_rir_surfaces() -> "list[ElmhurstRoomInRoofSurface]":
+    # A §3.9.1 Simplified Room-in-Roof lodges the roof-going Length/Height
+    # cells as placeholders (a 40 m flat-ceiling height, a 32 m slope on a
+    # 4.65 m gable) — Elmhurst ignores them and derives the area from the
+    # floor area. Gables ARE measured (4.65 × 2.45 = 11.39).
+    def surf(
+        name: str, length: float, height: float,
+        gable_type: Optional[str] = None, default_u: Optional[float] = None,
+    ) -> "ElmhurstRoomInRoofSurface":
+        return ElmhurstRoomInRoofSurface(
+            name=name, length_m=length, height_m=height, insulation="",
+            insulation_type=None, gable_type=gable_type,
+            default_u_value=default_u, u_value_known=False, u_value=0.0,
+        )
+
+    return [
+        surf("Flat Ceiling 1", 4.00, 40.00),   # placeholder
+        surf("Slope 1", 32.00, 32.00),          # placeholder
+        surf("Gable Wall 1", 4.65, 2.45, gable_type="Exposed", default_u=0.29),
+        surf("Gable Wall 2", 4.65, 2.45, gable_type="Party", default_u=0.25),
+    ]
+
+
+def test_elmhurst_simplified_rir_drops_placeholder_roof_surfaces() -> None:
+    # Arrange — RdSAP 10 §3.9.1 (PDF p.21): a Simplified RR's slope /
+    # flat ceiling / stud wall are not measured; emitting their
+    # placeholder L×H as `detailed_surfaces` makes the cascade bill them
+    # as explicit roof area (7.5× heat-loss explosion) instead of firing
+    # the spec's `A_RR = 12.5√(A_floor/1.5) − Σwalls` residual formula.
+    rir = ElmhurstRoomInRoof(
+        floor_area_m2=29.75, construction_age_band="A",
+        assessment="Simplified Type 1", surfaces=_placeholder_rir_surfaces(),
+    )
+
+    # Act
+    mapped = _map_elmhurst_room_in_roof(rir)
+
+    # Assert — roof-going surfaces dropped, both gables retained.
+    assert mapped is not None
+    kinds = sorted(s.kind for s in (mapped.detailed_surfaces or []))
+    assert "slope" not in kinds
+    assert "flat_ceiling" not in kinds
+    assert kinds == ["gable_wall", "gable_wall_external"]
+
+
+def test_elmhurst_detailed_rir_keeps_roof_surfaces() -> None:
+    # Arrange — a Detailed (§3.10) assessment DOES measure slope / flat
+    # ceiling, so they must be retained (regression guard so the
+    # Simplified drop doesn't bleed into Detailed lodgements).
+    rir = ElmhurstRoomInRoof(
+        floor_area_m2=29.75, construction_age_band="A",
+        assessment="Detailed", surfaces=_placeholder_rir_surfaces(),
+    )
+
+    # Act
+    mapped = _map_elmhurst_room_in_roof(rir)
+
+    # Assert — slope + flat ceiling retained under the Detailed path.
+    assert mapped is not None
+    kinds = sorted(s.kind for s in (mapped.detailed_surfaces or []))
+    assert "slope" in kinds
+    assert "flat_ceiling" in kinds
+
+
 def test_elmhurst_gas_boiler_main_fuel_derives_carrier_from_water_heating() -> None:
     # Arrange — SAP 10.2 Table 4b (PDF p.168) rows 101-119 are "Gas
     # boilers (including mains gas, LPG and biogas)". The code identifies
@@ -2731,6 +3145,55 @@ def test_space_heating_off_peak_fallback_uses_actual_tariff_low_rate_not_e7() ->
     assert abs(cost_eighteen_hour - 0.0741) <= 1e-6
 
 
+def test_space_heating_electric_room_heater_off_peak_bills_at_direct_acting_high_rate() -> None:
+    # Arrange — an ELECTRIC room heater (RdSAP main_heating_category 10,
+    # e.g. SAP code 691) is direct-acting electric, so SAP 10.2 Table 12a
+    # Grid 1 (PDF p.191) puts it on the "Other systems including direct-
+    # acting electric" row: 7-hour high-rate fraction 1.00, 10-hour 0.50.
+    # Unlike STORAGE heaters (category 7), which charge off-peak and so
+    # correctly bill 100% at the low rate, a room heater runs on demand —
+    # mostly at the HIGH rate. `_table_12a_system_for_main` only mapped
+    # ASHP, so a room heater fell through to the "100% low-rate" fallback
+    # (5.50 p, £0.0550), under-charging space heating by ~9.79 p/kWh and
+    # systematically OVER-rating the cat-10 cluster (1,000-cert API sample:
+    # 48 certs, mean |err| 9.49, signed +5.08). The fix maps electric
+    # cat-10 mains to OTHER_DIRECT_ACTING_ELECTRIC. Mirror of S0380.228
+    # (which fixed the same fallback for electric SECONDARY heating).
+    from domain.sap10_calculator.tables.table_12a import Tariff
+    electric_room_heater_main = MainHeatingDetail(
+        has_fghrs=False,
+        main_fuel_type=30,  # standard electricity
+        heat_emitter_type=2,
+        emitter_temperature=1,
+        main_heating_control=2602,
+        main_heating_category=10,  # electric room heaters
+        sap_main_heating_code=691,
+    )
+    gas_room_heater_main = MainHeatingDetail(
+        has_fghrs=False,
+        main_fuel_type=1,  # mains gas — NOT electric
+        heat_emitter_type=2,
+        emitter_temperature=1,
+        main_heating_control=2602,
+        main_heating_category=10,  # gas room heater (also cat 10)
+        sap_main_heating_code=631,
+    )
+
+    # Act — 7-hour off-peak tariff.
+    electric_rate = _space_heating_fuel_cost_gbp_per_kwh(
+        electric_room_heater_main, Tariff.SEVEN_HOUR, prices=SAP_10_2_SPEC_PRICES,
+    )
+    gas_rate = _space_heating_fuel_cost_gbp_per_kwh(
+        gas_room_heater_main, Tariff.SEVEN_HOUR, prices=SAP_10_2_SPEC_PRICES,
+    )
+
+    # Assert — electric room heater: 1.00 × 15.29 p = £0.1529 (high rate).
+    # Gas room heater is unaffected (non-electric → single Table 32 rate,
+    # not the off-peak electric split).
+    assert abs(electric_rate - 0.1529) <= 1e-6
+    assert abs(gas_rate - 0.0550) > 1e-6
+
+
 def test_heat_network_dlf_full_table_12c_age_band_coverage() -> None:
     # Arrange — SAP 10.2 Table 12c (page 193) heat-network Distribution
     # Loss Factor by dwelling age band A..M. None → K-or-newer
@@ -3886,6 +4349,110 @@ def test_air_source_heat_pump_pcdb_104568_derives_apm_efficiencies_per_sap_app_n
     )
 
 
+def test_loose_jacket_cylinder_computes_storage_loss_via_table2_loose_jacket_branch() -> None:
+    """SAP 10.2 Table 2 (PDF p.158) Note 1 gives a SEPARATE storage loss
+    factor for a loose-jacket cylinder: L = 0.005 + 1.76 / (t + 12.8),
+    ~2× the factory-insulated L = 0.005 + 0.55 / (t + 4.0) at the same
+    thickness. The EPB API lodges cylinder_insulation_type=2 = loose
+    jacket (1 = factory-applied). Before this fix
+    `_cylinder_storage_loss_override` returned None for every non-factory
+    type, so a loose-jacket cylinder fell to the zero-storage-loss combi
+    default — a systematic HW under-count (a 2026 register sample of 22
+    such certs over-predicted SAP by +2.29 mean). The override must route
+    insulation_type=2 to the Table 2 loose-jacket branch.
+    """
+    # Arrange — identical to the factory storage-loss test but
+    # cylinder_insulation_type=2 (loose jacket) instead of 1.
+    from domain.sap10_calculator.worksheet.water_heating import (
+        cylinder_storage_loss_factor_table_2,
+        cylinder_temperature_factor_table_2b,
+        cylinder_volume_factor_table_2a,
+    )
+
+    hp_main = MainHeatingDetail(
+        has_fghrs=False,
+        main_fuel_type=29,
+        heat_emitter_type=1,
+        emitter_temperature=1,
+        main_heating_control=2206,
+        main_heating_category=4,
+        sap_main_heating_code=None,
+    )
+    epc = make_minimal_sap10_epc(
+        total_floor_area_m2=_TYPICAL_TFA_M2,
+        habitable_rooms_count=4,
+        country_code="ENG",
+        has_hot_water_cylinder=True,
+        sap_building_parts=[make_building_part()],
+        sap_heating=make_sap_heating(
+            main_heating_details=[hp_main],
+            water_heating_code=901,
+            cylinder_size=3,  # Medium → 160 L
+            cylinder_insulation_type=2,  # loose jacket
+            cylinder_insulation_thickness_mm=50,
+            cylinder_thermostat="Y",
+        ),
+    )
+    # Expected (56)m Jan from the Table 2 loose-jacket branch (same V /
+    # VF / TF as the factory test — only the loss factor L differs).
+    loss_factor = cylinder_storage_loss_factor_table_2(
+        insulation_type="loose_jacket", thickness_mm=50.0
+    )
+    vol_factor = cylinder_volume_factor_table_2a(160.0)
+    temp_factor = cylinder_temperature_factor_table_2b(
+        has_cylinder_thermostat=True, separately_timed_dhw=True
+    )
+    expected_jan_kwh = 160.0 * loss_factor * vol_factor * temp_factor * 31
+
+    # Act
+    wh_result, _ = _water_heating_worksheet_and_gains(
+        epc=epc,
+        water_efficiency_pct=1.7,
+        is_instantaneous=False,
+        primary_age="D",
+        pcdb_record=None,
+    )
+
+    # Assert — non-None (was the zero-loss default) and equal to the
+    # loose-jacket branch, distinctly larger than the factory 36.9530.
+    assert wh_result is not None
+    got_jan_kwh = wh_result.solar_storage_monthly_kwh[0]
+    assert abs(got_jan_kwh - expected_jan_kwh) < 1e-4
+    assert got_jan_kwh > 36.9530  # loose jacket loses more than factory
+
+
+def test_no_water_heating_default_age_a_to_f_uses_12mm_loose_jacket_per_table_29() -> None:
+    """RdSAP 10 §10.7 + Table 29 (PDF p.55-56): when no water heating
+    system is lodged, the default cylinder takes the age-band insulation,
+    and "Age band of main property A to F: 12 mm loose jacket". Bands
+    A-F previously raised UnmappedSapCode because the loose-jacket storage
+    loss branch wasn't plumbed (now it is, S0380.224). A band-B cert must
+    resolve to a 12 mm loose-jacket cylinder; band G stays 25 mm factory.
+    """
+    from domain.sap10_calculator.rdsap.cert_to_inputs import _apply_rdsap_no_water_heating_system_default  # pyright: ignore[reportPrivateUsage]
+
+    def _no_dhw_epc(age_band: str) -> EpcPropertyData:
+        return make_minimal_sap10_epc(
+            total_floor_area_m2=_TYPICAL_TFA_M2,
+            habitable_rooms_count=4,
+            country_code="ENG",
+            sap_building_parts=[make_building_part(construction_age_band=age_band)],
+            sap_heating=make_sap_heating(water_heating_code=999),
+        )
+
+    # Act — band B (A-F band) + band G (factory band, regression guard).
+    band_b = _apply_rdsap_no_water_heating_system_default(_no_dhw_epc("B"))
+    band_g = _apply_rdsap_no_water_heating_system_default(_no_dhw_epc("G"))
+
+    # Assert — band B → 12 mm loose jacket (type 2); band G → 25 mm
+    # factory (type 1). Both gain the immersion + 110 L cylinder default.
+    assert band_b.has_hot_water_cylinder is True
+    assert band_b.sap_heating.cylinder_insulation_type == 2  # loose jacket
+    assert band_b.sap_heating.cylinder_insulation_thickness_mm == 12
+    assert band_g.sap_heating.cylinder_insulation_type == 1  # factory
+    assert band_g.sap_heating.cylinder_insulation_thickness_mm == 25
+
+
 def test_cert_with_hot_water_cylinder_computes_primary_loss_59m_from_sap_table_3() -> None:
     """SAP 10.2 §4 line 7700 + Table 3 (PDF p.159) define the primary
     circuit loss for an indirect cylinder:
@@ -5744,3 +6311,105 @@ def test_sap_appendix_d_eq_d1_water_efficiency_monthly_for_non_pcdb_table_4b_boi
         f"want {expected_hw_fuel!r} per SAP 10.2 Appendix D §D2.1 (2) "
         f"Equation D1 with Table 4b code 127 (winter 84%, summer 72%)"
     )
+
+
+def test_heat_network_community_gas_fuel_translates_epc_20_to_table12_51() -> None:
+    # Arrange — a community mains-gas BOILER main (SAP code 301) lodges
+    # main_fuel_type=20. Per epc_codes.csv (RdSAP-Schema-17.0) EPC fuel 20
+    # is "mains gas (community)", but the SAP Table 12 / Table 32 numbering
+    # uses 20 for a solid biomass fuel — a collision. The factor lookups
+    # check the Table-12 dict first, so co2_factor_kg_per_kwh(20) returns
+    # the biomass 0.028 instead of community mains gas 0.210. The
+    # heat-network fuel-code translator must route EPC 20 → Table 12 51.
+    from domain.sap10_calculator.tables.table_12 import (
+        co2_factor_kg_per_kwh,
+        primary_energy_factor,
+    )
+
+    main = MainHeatingDetail(
+        has_fghrs=False,
+        main_fuel_type=20,  # EPC "mains gas (community)"
+        heat_emitter_type=1,
+        emitter_temperature=1,
+        main_heating_control=2306,
+        main_heating_category=6,  # heat network
+        sap_main_heating_code=301,  # community boilers
+    )
+
+    # Act
+    code = _heat_network_factor_fuel_code(main)
+
+    # Assert — translates to Table 12 code 51 (community mains gas), and the
+    # factor lookups then return the worksheet-validated case-14 values
+    # ((367) CO2 0.2100, (467) PE 1.1300), NOT the collided biomass factors.
+    assert code == 51
+    assert abs(co2_factor_kg_per_kwh(code) - 0.210) <= 1e-9
+    assert abs(primary_energy_factor(code) - 1.130) <= 1e-9
+    assert abs(co2_factor_kg_per_kwh(20) - 0.028) <= 1e-9  # the collided value
+
+
+def test_non_heat_network_biomass_fuel_not_translated() -> None:
+    # Arrange — a NON-heat-network main lodging the same integer fuel code
+    # must NOT be translated: a genuine biomass boiler keeps its raw
+    # Table-12 factor. The translator only fires for heat-network mains.
+    main = MainHeatingDetail(
+        has_fghrs=False,
+        main_fuel_type=20,
+        heat_emitter_type=1,
+        emitter_temperature=1,
+        main_heating_control=2106,
+        main_heating_category=2,  # ordinary boiler, NOT heat network
+        sap_main_heating_code=102,
+    )
+
+    # Act
+    code = _heat_network_factor_fuel_code(main)
+
+    # Assert — unchanged (raw code, biomass factor preserved).
+    assert code == 20
+
+
+def test_heat_network_space_and_water_standing_charge_is_full_120() -> None:
+    # Arrange — a heat-network SPACE main (SAP code 301) carries the full
+    # Table 12 (PDF p.191) heat-network standing charge of £120/yr per
+    # §C3.2 ("the total standing charge is the normal heat network standing
+    # charge" when space heating is on the network). Worksheet-validated:
+    # case 14 (community boilers + mains gas, space + water) → (351) £120.
+    # The epc is not consulted on this branch (heat-network space main wins
+    # first), so a minimal epc suffices.
+    epc = _typical_semi_detached_epc()
+    main = MainHeatingDetail(
+        has_fghrs=False,
+        main_fuel_type=20,  # EPC mains gas (community)
+        heat_emitter_type=1,
+        emitter_temperature=1,
+        main_heating_control=2306,
+        main_heating_category=6,
+        sap_main_heating_code=301,
+    )
+
+    # Act
+    standing = _heat_network_standing_charge_gbp(epc, main)
+
+    # Assert
+    assert standing is not None
+    assert abs(standing - 120.0) <= 1e-9
+
+
+def test_non_heat_network_main_returns_none_so_caller_uses_fuel_standing() -> None:
+    # Arrange — a non-heat-network gas-boiler main must NOT draw the
+    # heat-network standing branch; the helper returns None so the caller
+    # falls back to the fuel-based `additional_standing_charges_gbp`.
+    epc = _typical_semi_detached_epc()
+    main = MainHeatingDetail(
+        has_fghrs=False,
+        main_fuel_type=26,  # mains gas (not community)
+        heat_emitter_type=1,
+        emitter_temperature=1,
+        main_heating_control=2106,
+        main_heating_category=2,
+        sap_main_heating_code=102,
+    )
+
+    # Act / Assert
+    assert _heat_network_standing_charge_gbp(epc, main) is None

tests/domain/sap10_calculator/rdsap/test_golden_fixtures.py

@@ -41,6 +41,7 @@ from domain.sap10_calculator.rdsap.cert_to_inputs import (
     SAP_10_2_SPEC_PRICES,
     cert_to_demand_inputs,
     cert_to_inputs,
+    heat_transmission_section_from_cert,
 )
 
 _FIXTURES_DIR = Path(__file__).parent / "fixtures" / "golden"
@@ -82,8 +83,8 @@ _EXPECTATIONS: tuple[_GoldenExpectation, ...] = (
         cert_number="0240-0200-5706-2365-8010",
         actual_sap=73,
         expected_sap_resid=-1,
-        expected_pe_resid_kwh_per_m2=+5.8007,
-        expected_co2_resid_tonnes_per_yr=+0.3173,
+        expected_pe_resid_kwh_per_m2=+1.5181,
+        expected_co2_resid_tonnes_per_yr=+0.0728,
         notes=(
             "Detached house, TFA 118, age J, oil boiler PCDB-listed + PV + "
             "RR on BP[0]. Mapper DOES extract sap_room_in_roof.room_in_roof_"
@@ -120,7 +121,103 @@ _EXPECTATIONS: tuple[_GoldenExpectation, ...] = (
             "extract-fans default (age J, 4 hab rooms → 2 fans). "
             "Cascade ventilation HLC rises ~0.07 ACH × volume → SH "
             "demand rises proportionally; PE +2.5225 → +5.8007, CO2 "
-            "+0.1395 → +0.3173. SAP integer unchanged at 72."
+            "+0.1395 → +0.3173. SAP integer unchanged at 72. "
+            "Slice S0380.196 (the 6035 RR fix) also applies here: this "
+            "cert's `room_in_roof_type_1` lodges two gables (L=6.4, both "
+            "Party) with no height, previously dropped → roof over-count. "
+            "Routing them through `detailed_surfaces` deducts 2×(6.4×2.45) "
+            "from the A_RR shell → roof drops, tightening PE +5.8007 → "
+            "+3.9138, CO2 +0.3173 → +0.2213. SAP integer unchanged at 72. "
+            "Slice S0380.198 CLOSED the SAP: this cert lodges 6 windows "
+            "with `window_wall_type=4` = roof windows ('Roof of Room' "
+            "rooflights). The API mapper had flattened them into "
+            "`sap_windows` (vertical glazing, (27), U=2.0); they belong on "
+            "(27a) at the Table 6e Note 2 inclination-adjusted U=2.30 with "
+            "45°-inclined solar gains. Validated against the simulated-"
+            "case-6 worksheet ((27a) U_eff 2.1062). The inclined solar "
+            "gain dominates → SAP cont 72.14 → 72.55 (resid -1 → +0 "
+            "EXACT), PE +3.9138 → +1.9459, CO2 +0.2213 → +0.1226. "
+            "Slice S0380.201 added the SECOND main heating system's "
+            "circulation pump per SAP 10.2 Table 4f note c) (PDF p.175) "
+            "\"Where there are two main heating systems include two "
+            "figures from this table\" — gated on a lodged "
+            "main_heating_fraction > 0 (a genuine second SPACE-heating "
+            "main, excluding DHW-only second mains). This cert is dual-"
+            "main oil combi 51%/49%; Main 2 pump_age unknown (115 kWh) "
+            "joins Main 1's 115 → cascade pumps_fans 315 → 430 (+115 "
+            "kWh/yr). The fix was validated against the simulated-case-6 "
+            "worksheet, whose (231) = 356 decomposes as (230c) central-"
+            "heating pump 156 (= Main 1 41 + Main 2 115) + (230d) oil "
+            "boiler pump 200 — proving the two-pump treatment is spec-"
+            "correct. Cascade SAP cont 72.55 → 72.18 (integer 73 → 72, "
+            "resid +0 → -1), PE +1.9459 → +2.8092, CO2 +0.1226 → "
+            "+0.1385. The lodged 73 carries Elmhurst's own rounding/"
+            "residual (this cert is API-only with no worksheet); the "
+            "worksheet-backed case 6 is the spec authority for the "
+            "archetype per [[feedback-worksheet-not-api-reference]]. "
+            "Slice S0380.202 added the SECOND main's central-heating-pump "
+            "GAIN per SAP 10.2 Table 5a note a) (PDF p.177) \"two main "
+            "heating systems serving different parts ... include two "
+            "figures\" — the §5 (70) mirror of S0380.201's Table 4f (230c). "
+            "Both Main 1 + Main 2 unknown-date → (70) 7 → 14 W. The extra "
+            "internal gain lowers space-heating demand → SAP cont 72.18 → "
+            "72.24 (integer 72 unchanged), PE +2.8092 → +2.5812, CO2 "
+            "+0.1385 → +0.1269 (both closer to zero). Validated against "
+            "case 6 worksheet (70) = 10 (= 3 Main 1 + 7 Main 2). "
+            "Slice S0380.203 routed this cert's 6 'Roof of Room' rooflights "
+            "(window_wall_type=4) to deduct from the §3.10.1 RR residual "
+            "instead of the regular roof (the case-6 worksheet rule). 0240 "
+            "is detailed-RR gables-only like case 6 → roof drops → space-"
+            "heating demand falls → PE +2.5812 → +2.1519, CO2 +0.1269 → "
+            "+0.1051 (both closer to zero; SAP integer 72 unchanged). "
+            "Slice S0380.205 applied the SAP 10.2 p.186 two-systems-"
+            "different-parts MIT (Main 1 2106 type 2 / Main 2 2110 type 3, "
+            "emitter 2 R=0.75): weighted responsiveness 0.8775 + elsewhere "
+            "two-control blend. Lowers MIT ~0.037 °C → space-heating demand "
+            "falls → PE +2.1519 → +1.6893, CO2 +0.1051 → +0.0815 (both "
+            "closer to zero; SAP integer 72 unchanged). Verified 1e-4 "
+            "against the case-6 worksheet (87)/(90)/(98c). "
+            "Slice S0380.206 fed Eq D1 the DHW boiler's OWN (204) space "
+            "share (Main 1 = 51%) instead of the dwelling total (202) — "
+            "the worksheet-validated case-6 fix that lands its (219) HW "
+            "exact. For 0240 this raises HW fuel slightly → PE +1.6893 → "
+            "+1.8687, CO2 +0.0815 → +0.0907 (SAP 72 unchanged). The lodged "
+            "73 carries Elmhurst's own residual; case 6 is the spec "
+            "authority per [[feedback-worksheet-not-api-reference]]. "
+            "Slice S0380.209 fixed the API-path wall U: the EPC renders "
+            "this cert's sandstone (band J, As Built) wall as 'insulated "
+            "(assumed)', which the cascade wrongly routed to the 50 mm "
+            "retrofit row (U 0.25). Per RdSAP 10 Table 8/9 footnote the "
+            "50 mm row is only for insulation 'known to have been "
+            "increased subsequently'; an 'as built ... (assumed)' "
+            "description is the age-band assumption (renders only on "
+            "recent bands) → as-built row U 0.35. Worksheet-validated by "
+            "simulated case 9 (sandstone J → 0.35) + case 10 (solid brick "
+            "J → 0.35). walls 24.45 → 34.23 W/K → PE +1.8687 → +5.5044, "
+            "CO2 +0.0907 → +0.2757 (SAP 72 unchanged). This spec-correct "
+            "fix REMOVED the wall under-count that was masking the Ext1 "
+            "vaulted-roof over-count (cascade U 0.68 via the same "
+            "'insulated (assumed)' description vs case-9 sloping-ceiling "
+            "0.25) — that roof over-count is the next slice; fixing both "
+            "lands SAP cont ≈ 72.31 (= Elmhurst case 9). The lodged 73 "
+            "requires a 2013+ pump (case 7); 0240's API lodges the pump "
+            "as Unknown (code 0 → 115, proven 0=Unknown across 9 API+"
+            "Summary pairs), so 73 is unreachable from the lodged inputs. "
+            "Slice S0380.211 fixed the Ext1 vaulted-roof over-count S0380.209 "
+            "exposed: BP2 lodges roof_construction=5 (vaulted), NI thickness, "
+            "'Pitched, insulated (assumed)', band J → the cascade returned "
+            "U 0.68 (the §5.11.4 retrofit-50 mm joist row). A vaulted ceiling "
+            "has no joist void, so per RdSAP 10 Table 18 it takes the column "
+            "(1) age-band default (band J = 0.16) — the SAME value the 33 "
+            "cohort-2 'ND' vaulted roofs (code 5, band D → 0.40 = col 1) "
+            "reach by falling through. New u_roof `is_sloping_ceiling` flag "
+            "(threaded from heat_transmission for codes 5/8) routes the 'NI' "
+            "variant to col (1) too. roof 76.93 → ~68 W/K → PE +5.5044 → "
+            "+1.5181, CO2 +0.2757 → +0.0728 (SAP integer 72 unchanged — the "
+            "true value; the lodged 73 needs the unpreserved 2013+ pump). "
+            "NB the S0380.209 note's predicted 'cont ≈ 72.31 (case 9, U 0.25 "
+            "col 3)' was an unconfirmed guess; the cohort's 'ND' vaulted "
+            "roofs are the arbiter and use col (1) 0.16 → cont 72.4617."
         ),
     ),
     _GoldenExpectation(
@@ -154,9 +251,9 @@ _EXPECTATIONS: tuple[_GoldenExpectation, ...] = (
     _GoldenExpectation(
         cert_number="0390-2954-3640-2196-4175",
         actual_sap=60,
-        expected_sap_resid=+7,
-        expected_pe_resid_kwh_per_m2=-27.9745,
-        expected_co2_resid_tonnes_per_yr=-2.7134,
+        expected_sap_resid=+0,
+        expected_pe_resid_kwh_per_m2=+0.5281,
+        expected_co2_resid_tonnes_per_yr=-0.1189,
         notes=(
             "Detached, TFA 360, age F, Firebird oil combi PCDF 9005 "
             "(winter eff 86.4%). PCDB record lodges separate_dhw_tests=0 + "
@@ -187,15 +284,26 @@ _EXPECTATIONS: tuple[_GoldenExpectation, ...] = (
             "Slice S0380.151 wired RdSAP 10 §4.1 Table 5 (PDF p.28) "
             "extract-fans default (age F → 1 fan). Cascade ventilation "
             "HLC rises ~0.03 ACH × volume; PE -28.0830 → -27.9745 "
-            "(closer to zero), CO2 -2.7342 → -2.7134."
+            "(closer to zero), CO2 -2.7342 → -2.7134. "
+            "Slice S0380.210 CLOSED the residual: the Main cavity wall lodges "
+            "wall_insulation_type=4 (as-built/assumed) + description "
+            "'Cavity wall, as built, partial insulation (assumed)'. The "
+            "cascade mis-routed it to the Table 6 'Filled cavity' row "
+            "(band F = 0.40) via the 'partial insulation' substring; "
+            "RdSAP 10 Table 6 (England) routes an as-built partial-fill "
+            "cavity to the 'Cavity as built' row (band F = 1.0). New "
+            "`_cavity_described_as_filled` excludes 'partial insulation' "
+            "(keeping 'insulated (assumed)' → filled). Wall HLC +53.6 W/K "
+            "(0.40 → 1.0 over 268 m²) lifted all four metrics together: "
+            "SAP +7 → +0, PE -27.9745 → +0.5281, CO2 -2.7134 → -0.1189."
         ),
     ),
     _GoldenExpectation(
         cert_number="6035-7729-2309-0879-2296",
         actual_sap=70,
-        expected_sap_resid=-2,
-        expected_pe_resid_kwh_per_m2=+19.1566,
-        expected_co2_resid_tonnes_per_yr=+0.4211,
+        expected_sap_resid=+0,
+        expected_pe_resid_kwh_per_m2=-0.1357,
+        expected_co2_resid_tonnes_per_yr=-0.0362,
         notes=(
             "Mid-terrace, TFA 128, age A, gas combi Table 4b code 104. "
             "S0380.189 fixed the dominant driver: walls are solid brick "
@@ -223,15 +331,47 @@ _EXPECTATIONS: tuple[_GoldenExpectation, ...] = (
             "WHC=901 + main code 104). Eq D1 monthly blend (mean ~80%) "
             "produces ~150 kWh/yr more HW fuel than the pre-slice flat-"
             "winter calc → PE residual +46.0952 → +47.2928, CO2 +1.0495 "
-            "→ +1.0779."
+            "→ +1.0779. "
+            "Slice S0380.196 CLOSED the residual (the prior 'lodged "
+            "divergence' claim is RETRACTED — it was a real API-mapper "
+            "bug). The API `room_in_roof_type_1` block lodges two gable "
+            "walls (L=4.65 each) but no heights; the mapper carried only "
+            "the scalar lengths, and the cascade's `_part_geometry` gable "
+            "formula silently drops height-less gables → the whole "
+            "55.67 m² A_RR shell billed as roof at U_RR=2.30 instead of "
+            "the §3.9.1(e) residual `12.5√(29.75/1.5) − 2×11.39 = 32.89`. "
+            "That over-counted roof by 22.78 m² × 2.30 = +52.4 W/K (roof "
+            "130.73 → 78.33, matching the site-notes case-4 replica at "
+            "1e-4). Fix: route the Type 1 gables through `detailed_"
+            "surfaces` (gable area = L × the §3.9.1 default RR storey "
+            "height 2.45 m; Exposed → gable_wall_external, Party → "
+            "gable_wall) so the cascade's Detailed-RR residual fires. "
+            "SAP resid -2 → +0 (exact), PE +19.16 → +1.84, CO2 "
+            "+0.42 → +0.01. "
+            "Slice S0380.198 (the 0240 roof-window fix) also applies: "
+            "6035 lodges 2 windows with `window_wall_type=4` (room-in-roof "
+            "rooflights) which were billed as vertical glazing; routing "
+            "them to roof windows (27a) at inclined U=2.30 + 45° solar "
+            "tightened PE +1.84 → +1.37 and CO2 +0.01 → -0.0004 (SAP still "
+            "exact). "
+            "Slice S0380.203 CLOSED the remaining +1.37 PE (it was NOT "
+            "'unrelated gains/HW'): the 2 'Roof of Room' rooflights pierce "
+            "the room-in-roof sloped ceiling, so their 1.92 m² deducts from "
+            "the §3.10.1 RR residual (uninsulated U_RR=2.30) — not the "
+            "insulated loft (U=0.14) the S0380.198 assumption used. Roof "
+            "78.0648 → 73.9176 (−4.42 W/K); space-heating demand drops → "
+            "PE +1.37 → -0.14, CO2 -0.0004 → -0.0362 (SAP still exact 70). "
+            "Validated against the simulated-case-6 worksheet, the only "
+            "worksheet evidence for 'Roof of Room' rooflight deduction "
+            "(6035's site-notes case-4 replica lodges no rooflights)."
         ),
     ),
     _GoldenExpectation(
         cert_number="7536-3827-0600-0600-0276",
         actual_sap=68,
         expected_sap_resid=+1,
-        expected_pe_resid_kwh_per_m2=-7.0776,
-        expected_co2_resid_tonnes_per_yr=-0.1875,
+        expected_pe_resid_kwh_per_m2=-6.1952,
+        expected_co2_resid_tonnes_per_yr=-0.1639,
         notes=(
             "Detached + 2 extensions, TFA 152. Multi-age bps (Main=D, "
             "Ext1=L, Ext2=F). Slice 59 (per-bp window apportionment) and "
@@ -239,10 +379,31 @@ _EXPECTATIONS: tuple[_GoldenExpectation, ...] = (
             "age band, not per-bp) jointly tightened: SAP +4 → +3, PE "
             "-27.17 → -22.53, CO2 -0.72 → -0.60. Slice 97 added "
             "glazing_type=2 (Table 24 spec U=2.0): SAP 0 → +1, PE/CO2 "
-            "widened. The cert's actual lodged U for glazing_type=2 "
-            "appears higher than the spec's table default — multi-age "
-            "geometry probably surfaces a per-bp U-value the spec table "
-            "doesn't capture exactly."
+            "widened. Slice S0380.214 fixed the as-built sloping-ceiling "
+            "roof U: Ext1 (band L) and Ext2 (band F) lodge "
+            "roof_construction=8 'Pitched, sloping ceiling' + 'As Built', "
+            "which take RdSAP 10 Table 18 col (3) (L=0.18, F=0.68) not "
+            "col (1) (0.16/0.40) — per item 5-5 + note (b). Roof HLC "
+            "26.77 → 29.17 W/K; cont SAP 69.071 → 68.924, PE -7.0776 → "
+            "-6.1952, CO2 -0.1875 → -0.1639 (SAP integer still 68 vs "
+            "lodged → resid +1). Worksheet-validated by simulated case 15 "
+            "(the 7536 replica): our cascade on its Summary matches the "
+            "P960 worksheet exactly (roof 29.17, SAP 65.04 vs 65). The "
+            "glazing hypothesis from the prior handover was wrong — maxing "
+            "the glazing U past spec can't flip 69→68, and every per-bp "
+            "fabric U is spec-plausible. CONCLUSION (cases 15/16/17, the "
+            "last faithful on windows 16.98/13.59/1.89 + ground floors): "
+            "every per-element value matches Elmhurst — walls 0.70/0.28/"
+            "0.40, roofs 0.40/0.18/0.68, window U-eff 2.4368/1.8519, "
+            "ground floors Main 0.97 / Ext1 0.26 / Ext2 1.12. The only "
+            "worksheet divergences were manual-entry artifacts (case 16 "
+            "floor-order inversion; case 17 spurious 'to external air' "
+            "exposed floors auto-derived from the small-ground/big-upper "
+            "geometry — real 7536 lodges floor_heat_loss 2/7/3 = unheated-"
+            "space/ground, NOT code 1 exposed). The residual +0.92 cont "
+            "SAP is therefore 0240-like: an Elmhurst register-rounding "
+            "residual not reproducible from the API-only JSON. DO NOT "
+            "chase further — leave at resid +1."
         ),
     ),
     _GoldenExpectation(
@@ -273,9 +434,9 @@ _EXPECTATIONS: tuple[_GoldenExpectation, ...] = (
     _GoldenExpectation(
         cert_number="2130-1033-4050-5007-8395",
         actual_sap=82,
-        expected_sap_resid=+1,
-        expected_pe_resid_kwh_per_m2=-7.5579,
-        expected_co2_resid_tonnes_per_yr=-0.0454,
+        expected_sap_resid=+2,
+        expected_pe_resid_kwh_per_m2=-11.7236,
+        expected_co2_resid_tonnes_per_yr=-0.0947,
         notes=(
             "End-terrace + 1 extension, TFA 64, gas combi PCDB index 17505, "
             "postcode DE22 (PCDB Table 172 match), PV: 2× 2.04 kWp arrays "
@@ -284,9 +445,28 @@ _EXPECTATIONS: tuple[_GoldenExpectation, ...] = (
             "from -38.63 to -9.70. Slice S0380.49 wired effective monthly "
             "Table 12e PE factor (vs annual 1.501/0.501) into the PV "
             "split: residual closed -9.70 → -8.22. SAP integer shifted "
-            "+1 (82 → 83) via the cohort cascade interaction. Remaining "
-            "-8.22 residual sits in gas combi PE under-count + secondary "
-            "heating credit (deferred)."
+            "+1 (82 → 83) via the cohort cascade interaction. "
+            "Slice S0380.215 fixed the dropped measured wall insulation: "
+            "Ext1 lodges solid-brick band B + INTERNAL insulation "
+            "`wall_insulation_thickness='measured'` with the actual 100 mm "
+            "in the separate `wall_insulation_thickness_measured` field "
+            "that the schema didn't declare, so `from_dict` discarded it "
+            "and the cascade fell back to the 50 mm unknown-thickness "
+            "default (U=0.55). Wiring it through → RdSAP 10 Table 8 U=0.32 "
+            "(less wall loss). This SPEC-CORRECT fix EXPOSED the offsetting "
+            "PV-β / gas-combi-PE under-count it had been masking: cont SAP "
+            "83.35 → 83.78 (resid +1 → +2), PE -7.56 → -11.72, CO2 -0.045 "
+            "→ -0.095. INVESTIGATED the exposed -11.72 PE (~-746 kWh/yr) "
+            "against simulated case 18 (a TFA-64 base + 2130's exact PV: 2× "
+            "2.04 kWp SE/NW, overshading 1/2): our cascade reproduces the "
+            "P960 worksheet's PV split EXACTLY — gen 2684.17, (233a) onsite "
+            "970.77, (233b) export 1713.40 to the decimal. So the Appendix "
+            "M1 β-split is NOT the bug; the gas PE factor is also exact "
+            "(Table 12 mains gas 1.13). 2130's residual is therefore the "
+            "irreducible API-only lodged gap (Elmhurst's own residual), "
+            "0240-like — NOT a closable calculator bug. The +2/-11.72 is "
+            "the spec-correct state once the masking wall bug is removed. "
+            "Leave it; do not chase."
         ),
     ),
     _GoldenExpectation(
@@ -486,6 +666,58 @@ _EXPECTATIONS: tuple[_GoldenExpectation, ...] = (
     _GoldenExpectation(cert_number="9421-3045-3205-1646-6200", actual_sap=87, expected_sap_resid=+0, expected_pe_resid_kwh_per_m2=-0.3541, expected_co2_resid_tonnes_per_yr=-0.0046, notes="Cohort-2 baseline pin captured by S0380.69."),
     _GoldenExpectation(cert_number="9796-3058-6205-0346-9200", actual_sap=90, expected_sap_resid=+0, expected_pe_resid_kwh_per_m2=-0.3533, expected_co2_resid_tonnes_per_yr=-0.0013, notes="Cohort-2 baseline pin captured by S0380.69."),
     _GoldenExpectation(cert_number="9836-7525-9500-0575-1202", actual_sap=75, expected_sap_resid=+0, expected_pe_resid_kwh_per_m2=-0.1132, expected_co2_resid_tonnes_per_yr=+0.0011, notes="Cohort-2 baseline pin captured by S0380.69."),
+
+    # ------------------------------------------------------------------
+    # "with api 3" — 2 fresh API+Summary+worksheet triples cross-validated
+    # by S0380.218. Both fetched fresh from the GOV.UK EPB register, run
+    # through BOTH front-ends (`from_api_response` + `from_elmhurst_site_
+    # notes`), and pinned against the dr87 worksheet. The two paths agree
+    # to <1e-4 on all four metrics (cross-mapper parity per
+    # [[feedback-cross-mapper-parity-via-cascade]]) AND reproduce the
+    # worksheet's (255) cost / (272) CO2 / (286) PE exactly — see the
+    # +0.0000 worksheet pins in `_WORKSHEET_PE_CO2`. The dropped-field
+    # audit on both fresh JSONs surfaced no new silently-dropped schema
+    # fields (only `created_at` metadata + the shower keys handled by
+    # `_normalize_shower_outlets`). The PE/CO2 residuals below are vs the
+    # integer-rounded lodged register (`energy_consumption_current` /
+    # `co2_emissions_current`); the worksheet pins are the load-bearing
+    # 1e-4 check.
+    # ------------------------------------------------------------------
+    _GoldenExpectation(
+        cert_number="0340-2467-9260-2006-6521",
+        actual_sap=70,
+        expected_sap_resid=+0,
+        expected_pe_resid_kwh_per_m2=-0.4054,
+        expected_co2_resid_tonnes_per_yr=-0.0250,
+        notes=(
+            "Semi-detached house, TFA 107.26, mains-gas PCDB-listed boiler "
+            "(index 15709, no Table 4b code), no PV, 1 building part, 17 "
+            "windows. S0380.218 cross-validation: API path ≡ Summary path "
+            "to <1e-4 on SAP/cost/CO2/PE; cascade reproduces the dr87 "
+            "worksheet (255) cost 776.4295 / (272) CO2 2875.0498 / (286) PE "
+            "16474.5616 exactly (see `_WORKSHEET_PE_CO2`). Cascade SAP "
+            "integer 70 = lodged (resid +0); cont 70.1228. PE/CO2 resids "
+            "below are vs the integer-rounded lodged register."
+        ),
+    ),
+    _GoldenExpectation(
+        cert_number="5500-5070-0822-0201-3663",
+        actual_sap=66,
+        expected_sap_resid=+0,
+        expected_pe_resid_kwh_per_m2=-0.2909,
+        expected_co2_resid_tonnes_per_yr=+0.0235,
+        notes=(
+            "Semi-detached house + 1 extension, TFA 82.88, mains-gas "
+            "PCDB-listed boiler (index 17741, no Table 4b code), no PV, 2 "
+            "building parts, 13 windows. S0380.218 cross-validation: API "
+            "path ≡ Summary path to <1e-4 on SAP/cost/CO2/PE; cascade "
+            "reproduces the dr87 worksheet (255) cost 751.8295 / (272) CO2 "
+            "2423.4547 / (286) PE 14397.0118 exactly (see "
+            "`_WORKSHEET_PE_CO2`). Cascade SAP integer 66 = lodged (resid "
+            "+0); cont 65.5539. PE/CO2 resids below are vs the integer-"
+            "rounded lodged register."
+        ),
+    ),
 )
 
 
@@ -517,7 +749,8 @@ class _WorksheetPin:
     expected_co2_resid_kg: float
 
 
-# The 47 worksheet-validated certs (9 ASHP + 38 cohort-2). calc ≡
+# The 49 worksheet-validated certs (9 ASHP + 38 cohort-2 + 2 "with api
+# 3", the last pair added by S0380.218). calc ≡
 # worksheet on BOTH PE and CO2 at <1e-4 across the ENTIRE cohort
 # (every expected_*_resid below is 0.0000) — the SAP 10.2 1e-4
 # convergence target, met. Closed over two slices:
@@ -542,6 +775,7 @@ _WORKSHEET_PE_CO2: tuple[_WorksheetPin, ...] = (
     _WorksheetPin(cert_number="0320-2756-8640-2296-1101", ws_pe_kwh_per_m2=45.7367, ws_co2_kg_per_yr=430.2596, expected_pe_resid=+0.0000, expected_co2_resid_kg=+0.0000),
     _WorksheetPin(cert_number="0330-2249-8150-2326-4121", ws_pe_kwh_per_m2=199.4413, ws_co2_kg_per_yr=3066.3286, expected_pe_resid=+0.0000, expected_co2_resid_kg=+0.0000),
     _WorksheetPin(cert_number="0330-2257-3640-2196-3145", ws_pe_kwh_per_m2=66.2620, ws_co2_kg_per_yr=435.0043, expected_pe_resid=+0.0000, expected_co2_resid_kg=+0.0000),
+    _WorksheetPin(cert_number="0340-2467-9260-2006-6521", ws_pe_kwh_per_m2=153.5946, ws_co2_kg_per_yr=2875.0498, expected_pe_resid=+0.0000, expected_co2_resid_kg=+0.0000),
     _WorksheetPin(cert_number="0350-2968-2650-2796-5255", ws_pe_kwh_per_m2=55.7024, ws_co2_kg_per_yr=470.7988, expected_pe_resid=+0.0000, expected_co2_resid_kg=+0.0000),
     _WorksheetPin(cert_number="0360-2266-5650-2106-8285", ws_pe_kwh_per_m2=162.9804, ws_co2_kg_per_yr=2183.7720, expected_pe_resid=+0.0000, expected_co2_resid_kg=+0.0000),
     _WorksheetPin(cert_number="0380-2471-3250-2596-8761", ws_pe_kwh_per_m2=56.4872, ws_co2_kg_per_yr=292.5490, expected_pe_resid=+0.0000, expected_co2_resid_kg=+0.0000),
@@ -567,6 +801,7 @@ _WORKSHEET_PE_CO2: tuple[_WorksheetPin, ...] = (
     _WorksheetPin(cert_number="4536-5424-8600-0109-1226", ws_pe_kwh_per_m2=63.9133, ws_co2_kg_per_yr=494.6357, expected_pe_resid=+0.0000, expected_co2_resid_kg=+0.0000),
     _WorksheetPin(cert_number="4536-8325-3100-0409-1222", ws_pe_kwh_per_m2=181.7206, ws_co2_kg_per_yr=2109.2633, expected_pe_resid=+0.0000, expected_co2_resid_kg=+0.0000),
     _WorksheetPin(cert_number="4800-3992-0422-0599-3563", ws_pe_kwh_per_m2=66.4814, ws_co2_kg_per_yr=259.3652, expected_pe_resid=+0.0000, expected_co2_resid_kg=+0.0000),
+    _WorksheetPin(cert_number="5500-5070-0822-0201-3663", ws_pe_kwh_per_m2=173.7091, ws_co2_kg_per_yr=2423.4547, expected_pe_resid=+0.0000, expected_co2_resid_kg=+0.0000),
     _WorksheetPin(cert_number="6835-3920-2509-0933-5226", ws_pe_kwh_per_m2=224.4924, ws_co2_kg_per_yr=1476.3032, expected_pe_resid=+0.0000, expected_co2_resid_kg=+0.0000),
     _WorksheetPin(cert_number="7700-3362-0922-7022-3563", ws_pe_kwh_per_m2=196.5859, ws_co2_kg_per_yr=2321.5875, expected_pe_resid=+0.0000, expected_co2_resid_kg=+0.0000),
     _WorksheetPin(cert_number="7800-1501-0922-7127-3563", ws_pe_kwh_per_m2=172.9406, ws_co2_kg_per_yr=3144.0259, expected_pe_resid=+0.0000, expected_co2_resid_kg=+0.0000),
@@ -731,3 +966,75 @@ def test_api_to_domain_mapper_preserves_main_heating_index_number(
     assert main.main_heating_index_number == expected_pcdb_id
     if expected_winter_eff is not None:
         assert abs(inputs.main_heating_efficiency - expected_winter_eff) <= 1e-3
+
+
+def test_0240_api_wall_type_4_windows_map_to_roof_windows() -> None:
+    """Cert 0240 lodges 6 windows with `window_wall_type=4` — the RdSAP
+    API code for a roof window ("Roof of Room" rooflight / inclined
+    glazing), distinct from main-wall (1) and alternative-wall (2/3)
+    windows. They belong on worksheet line (27a) Roof Windows at the
+    Table 6e Note 2 inclination-adjusted U (DG 2002+ vertical 2.0 + 0.30
+    = 2.30 W/m²K), with 45°-inclined solar gains — NOT on (27) as vertical
+    wall windows at U=2.0.
+
+    Before the fix the API mapper flattened all windows into
+    `sap_windows`, so these 6 billed as vertical glazing (wrong U *and*
+    wrong solar). Validated against the simulated-case-6 worksheet, which
+    bills the identical 6 windows on (27a) at U_eff 2.1062 (= 2.30 with
+    the §3.2 R=0.04 curtain transform).
+    """
+    # Arrange
+    doc = _load_cert("0240-0200-5706-2365-8010")
+
+    # Act
+    epc = EpcPropertyDataMapper.from_api_response(doc)
+
+    # Assert — the 6 wall_type=4 windows route to roof windows; the other
+    # 5 (wall_type=1, main wall) stay vertical.
+    assert epc.sap_roof_windows is not None
+    assert len(epc.sap_roof_windows) == 6
+    assert len(epc.sap_windows) == 5
+    assert all(abs(rw.u_value_raw - 2.30) <= 1e-9 for rw in epc.sap_roof_windows)
+
+
+def test_6035_api_room_in_roof_gables_deduct_from_roof() -> None:
+    """Cert 6035 lodges a Simplified Type 1 room-in-roof (`room_in_roof_
+    type_1`) with two gable walls (L=4.65 each). Per RdSAP 10 §3.9.1(e)
+    (PDF p.21) the gable areas deduct from the A_RR shell — the residual
+    roof area is `12.5√(A_RR_floor/1.5) − Σ gables`, NOT the full shell.
+
+    The API mapper must route these scalar gables through
+    `detailed_surfaces` (gable area = L × the §3.9.1 default RR storey
+    height 2.45 m) so the cascade's Detailed-RR residual fires, exactly
+    as the site-notes path does. Before the fix the gables (no lodged
+    height) were silently dropped → the whole 55.67 m² shell billed at
+    U_RR=2.30, a +52 W/K roof over-count and the entire 6035 residual.
+
+    Cross-mapper parity: this is the value the site-notes case-4 replica
+    (`worksheet/_elmhurst_worksheet_001431_6035.py`) pins to its
+    worksheet at 1e-4:
+      loft  (41.73−29.75=11.98) × U_roof(300 mm) = 1.6772
+      ext   (7.21)             × U_roof(300 mm)  = 1.0094
+      RR residual (55.67 − 2×11.39 = 32.89) × U_RR(age A=2.30) = 75.647
+      → 78.3336 W/K
+    """
+    # Arrange
+    doc = _load_cert("6035-7729-2309-0879-2296")
+    epc = EpcPropertyDataMapper.from_api_response(doc)
+
+    # Act
+    roof_w_per_k = heat_transmission_section_from_cert(epc).roof_w_per_k
+
+    # Assert — 78.3336 (gable-deducted residual + loft + ext roof). The 2
+    # room-in-roof rooflights (window_wall_type=4 = "Roof of Room", 1.92 m²)
+    # pierce the RR sloped ceiling, so per S0380.203 their area deducts from
+    # the §3.10.1 residual (at the uninsulated U_RR=2.30) — NOT the insulated
+    # loft at U_roof=0.14 as the unvalidated S0380.198 assumption had it.
+    # 78.3336 − 1.92 × 2.30 = 78.3336 − 4.416 = 73.9176. The rooflights' own
+    # A×U stays on roof_windows_w_per_k. This matches the simulated-case-6
+    # worksheet, where the only worksheet evidence for "Roof of Room"
+    # rooflight deduction shows them billed against "Roof room remaining"
+    # (the RR residual), not the flat/loft roof. Cert 6035 is API-only and
+    # its site-notes case-4 worksheet replica lodges no rooflights, so the
+    # case-6 worksheet is the spec authority for this archetype.
+    assert abs(roof_w_per_k - 73.9176) <= 1e-4

tests/domain/sap10_calculator/test_table_12a.py

@@ -17,12 +17,35 @@ from domain.sap10_calculator.tables.table_12a import (
     Table12aSystem,
     Tariff,
     other_use_high_rate_fraction,
+    rdsap_tariff_for_cert,
     space_heating_high_rate_fraction,
     tariff_from_meter_type,
     water_heating_high_rate_fraction,
 )
 
 
+def test_dual_meter_electric_room_heater_resolves_to_ten_hour_tariff() -> None:
+    # Arrange — RdSAP 10 §12 (PDF p.62) Dual-meter tariff dispatch: for a
+    # Dual meter the choice between 7-hour and 10-hour is made by the main
+    # heating type. Rule 3 verbatim: "if the main system ... is a direct-
+    # acting electric boiler (191), or electric room heaters ... it is
+    # 10-hour tariff." The electric room-heater codes are Table 4a 691
+    # (panel/convector/radiant), 692 (fan), 693 (portable), 694 (water-/
+    # oil-filled), 699 (assumed). Pre-slice these fell through to Rule 4
+    # (7-hour default), so a Dual-meter room-heater cert was billed at the
+    # 7-hour rates with Table 12a high-rate fraction 1.00 instead of the
+    # 10-hour rates with fraction 0.50 — over-charging direct-acting heat
+    # once S0380.230 routed it to OTHER_DIRECT_ACTING_ELECTRIC.
+
+    # Act / Assert — every electric room-heater code on a Dual meter → 10-hour.
+    for code in (691, 692, 693, 694, 699):
+        assert rdsap_tariff_for_cert(1, main_1_sap_code=code) is Tariff.TEN_HOUR
+    # Storage heaters (Rule 2) stay 7-hour; a gas room heater (non-Rule-3
+    # code) keeps the Rule 4 Dual default of 7-hour.
+    assert rdsap_tariff_for_cert(1, main_1_sap_code=401) is Tariff.SEVEN_HOUR
+    assert rdsap_tariff_for_cert(1, main_1_sap_code=601) is Tariff.SEVEN_HOUR
+
+
 def test_tariff_enum_has_five_members() -> None:
     """Table 12a columns: standard (no off-peak split), 7-hour, 10-hour,
     18-hour, 24-hour. Worksheet-shape fidelity: TEN_HOUR is included for

tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_000474.py

@@ -65,6 +65,8 @@ def build_epc() -> EpcPropertyData:
     """
     main = SapBuildingPart(
         identifier=BuildingPartIdentifier.MAIN,
+        # API parity: roof_construction int mirrors the gov-EPC mapper
+        roof_construction=4,
         construction_age_band="B",
         wall_construction=_WC_CAVITY,
         wall_insulation_type=4,
@@ -98,6 +100,8 @@ def build_epc() -> EpcPropertyData:
     )
     extension_1 = SapBuildingPart(
         identifier=BuildingPartIdentifier.EXTENSION_1,
+        # API parity: roof_construction int mirrors the gov-EPC mapper
+        roof_construction=4,
         construction_age_band="B",
         wall_construction=_WC_CAVITY,
         wall_insulation_type=4,
@@ -130,6 +134,8 @@ def build_epc() -> EpcPropertyData:
     )
     extension_2 = SapBuildingPart(
         identifier=BuildingPartIdentifier.EXTENSION_2,
+        # API parity: roof_construction int mirrors the gov-EPC mapper
+        roof_construction=3,
         construction_age_band="B",
         wall_construction=_WC_CAVITY,
         wall_insulation_type=4,

tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_000477.py

@@ -63,6 +63,8 @@ def build_epc() -> EpcPropertyData:
     """
     main = SapBuildingPart(
         identifier=BuildingPartIdentifier.MAIN,
+        # API parity: roof_construction int mirrors the gov-EPC mapper
+        roof_construction=4,
         construction_age_band="B",
         wall_construction=_WC_CAVITY,
         wall_insulation_type=4,

tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_000480.py

@@ -64,6 +64,8 @@ def build_epc() -> EpcPropertyData:
     """
     main = SapBuildingPart(
         identifier=BuildingPartIdentifier.MAIN,
+        # API parity: roof_construction int mirrors the gov-EPC mapper
+        roof_construction=4,
         construction_age_band="B",
         wall_construction=_WC_CAVITY,
         wall_insulation_type=4,
@@ -133,6 +135,8 @@ def build_epc() -> EpcPropertyData:
     )
     extension = SapBuildingPart(
         identifier=BuildingPartIdentifier.EXTENSION_1,
+        # API parity: roof_construction int mirrors the gov-EPC mapper
+        roof_construction=4,
         construction_age_band="B",
         wall_construction=_WC_CAVITY,
         wall_insulation_type=4,

tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_000487.py

@@ -60,6 +60,8 @@ def build_epc() -> EpcPropertyData:
     """
     main = SapBuildingPart(
         identifier=BuildingPartIdentifier.MAIN,
+        # API parity: roof_construction int mirrors the gov-EPC mapper
+        roof_construction=4,
         construction_age_band="B",
         wall_construction=_WC_CAVITY,
         wall_insulation_type=4,  # "A As Built"
@@ -130,6 +132,8 @@ def build_epc() -> EpcPropertyData:
     )
     extension = SapBuildingPart(
         identifier=BuildingPartIdentifier.EXTENSION_1,
+        # API parity: roof_construction int mirrors the gov-EPC mapper
+        roof_construction=4,
         construction_age_band="B",
         wall_construction=_WC_CAVITY,
         wall_insulation_type=4,

tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_000490.py

@@ -65,6 +65,8 @@ def build_epc() -> EpcPropertyData:
     """
     main = SapBuildingPart(
         identifier=BuildingPartIdentifier.MAIN,
+        # API parity: roof_construction int mirrors the gov-EPC mapper
+        roof_construction=4,
         construction_age_band="B",
         wall_construction=_WC_CAVITY,
         wall_insulation_type=4,
@@ -97,6 +99,8 @@ def build_epc() -> EpcPropertyData:
     )
     extension = SapBuildingPart(
         identifier=BuildingPartIdentifier.EXTENSION_1,
+        # API parity: roof_construction int mirrors the gov-EPC mapper
+        roof_construction=4,
         construction_age_band="B",
         wall_construction=_WC_CAVITY,
         wall_insulation_type=4,

tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_000516.py

@@ -69,6 +69,8 @@ def build_epc() -> EpcPropertyData:
     """
     main = SapBuildingPart(
         identifier=BuildingPartIdentifier.MAIN,
+        # API parity: roof_construction int mirrors the gov-EPC mapper
+        roof_construction=3,
         construction_age_band="A",
         wall_construction=_WC_CAVITY,
         wall_insulation_type=4,

tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_001431_6035.py

@@ -0,0 +1,114 @@
+"""Mapper-driven cascade pin against the Elmhurst P960-0001-001431
+"simulated case 4" worksheet — a near-exact replica of golden cert
+6035 (Main + Extension + Simplified room-in-roof, 8 windows).
+
+Like 000565 / sim case 1 / sim case 2, this fixture does NOT hand-build
+the EpcPropertyData: it routes the Summary PDF through
+ElmhurstSiteNotesExtractor + from_elmhurst_site_notes so the SAP-result
+pin grid exercises the WHOLE extractor + mapper + calculator pipeline.
+
+Purpose: prove the calculator is spec-correct for the 6035 archetype
+(after S0380.192 Simplified-RR + S0380.193 suspended-floor fixes). This
+cert reproduces 6035's full floor geometry — Main ground-floor HLP
+15.99 m AND first-floor HLP 8.32 m (the asymmetric upper-storey
+perimeter) — plus 6035's 8 windows (≈14.15 m²). Two minor inputs still
+differ from 6035 (the largest window's orientation is N here vs S in
+6035; meter type "Dual" vs API code 2), accounting for a residual ~50
+kWh / £11 cascade delta — both are lodged inputs, not calculator
+behaviour. All 11 Block-1 line refs pin at abs=1e-4 against this cert's
+OWN worksheet, confirming the cascade reproduces the spec engine exactly
+for 6035's geometry — so 6035's residual +19 PE vs the lodged register
+is lodged-register divergence, not a cascade gap.
+
+Cert shape: Main + Extension 1, both solid brick WITH internal
+insulation (Main) / as-built (Ext1), 3 storeys, Simplified room-in-roof
+on the Main (floor 29.75 m², exposed + party gables), suspended
+uninsulated ground floors (Main ground HLP 15.99 / first 8.32),
+gas-combi SAP code 104, 8 windows, no PV.
+
+Source: user-simulated PDFs at `sap worksheets/golden fixture
+debugging/simulated case 4/`. The Summary is mirrored into the tracked
+`backend/documents_parser/tests/fixtures/Summary_001431_6035.pdf`
+(distinct name — the corpus reuses cert 001431).
+
+Worksheet pin targets (P960-0001-001431, Block 1 — energy rating):
+- SAP rating 68 (line 258), ECF 2.2802 (line 257)
+- Total fuel cost £937.2341 (line 255)
+- CO2 4682.3494 kg/year (line 272)
+- Space heating 15745.3260 kWh/year (Σ monthly (98))
+- Main 1 fuel 18744.4357 kWh/year (line 211)
+- Secondary fuel 0.0 (line 215)
+- Hot water fuel 3307.8383 kWh/year (line 219)
+- Lighting 262.0885 kWh/year (line 232)
+- Pumps/fans 86.0 kWh/year (line 231)
+
+Per [[feedback-zero-error-strict]] + [[feedback-e2e-validation-
+philosophy]]: pins are abs=1e-4 against the worksheet PDF.
+"""
+
+from __future__ import annotations
+
+import re
+import subprocess
+from pathlib import Path
+from typing import Final
+
+from backend.documents_parser.elmhurst_extractor import ElmhurstSiteNotesExtractor
+from datatypes.epc.domain.epc_property_data import EpcPropertyData
+from datatypes.epc.domain.mapper import EpcPropertyDataMapper
+
+
+# parents[0]=worksheet/, [1]=sap10_calculator/, [2]=domain/, [3]=tests/,
+# [4]=repo root.
+_SUMMARY_PDF: Final[Path] = (
+    Path(__file__).resolve().parents[4]
+    / "backend" / "documents_parser" / "tests" / "fixtures"
+    / "Summary_001431_6035.pdf"
+)
+
+
+def _summary_pdf_to_textract_style_pages(pdf_path: Path) -> list[str]:
+    """Convert a Summary PDF into the per-page text format the
+    ElmhurstSiteNotesExtractor expects (label\\nvalue sequences).
+
+    Mirror of the helper in `test_summary_pdf_mapper_chain.py` /
+    `_elmhurst_worksheet_000565.py`.
+    """
+    info = subprocess.run(
+        ["pdfinfo", str(pdf_path)], capture_output=True, text=True, check=True,
+    ).stdout
+    m = re.search(r"Pages:\s+(\d+)", info)
+    if m is None:
+        raise RuntimeError(f"Could not parse page count from {pdf_path}")
+    page_count = int(m.group(1))
+
+    pages: list[str] = []
+    for i in range(1, page_count + 1):
+        layout = subprocess.run(
+            [
+                "pdftotext", "-layout", "-f", str(i), "-l", str(i),
+                str(pdf_path), "-",
+            ],
+            capture_output=True, text=True, check=True,
+        ).stdout
+        tokens: list[str] = []
+        for line in layout.splitlines():
+            if not line.strip():
+                tokens.append("")
+                continue
+            parts = [p for p in re.split(r"\s{2,}", line.strip()) if p]
+            tokens.extend(parts)
+        pages.append("\n".join(tokens))
+    return pages
+
+
+def build_epc() -> EpcPropertyData:
+    """Route the simulated case-2 Summary through extractor + mapper.
+
+    No hand-built EpcPropertyData — the extractor and mapper are part of
+    the test target. Exercises the S0380.192 Simplified-RR fix and the
+    S0380.193 suspended-floor sealed-rule fix.
+    """
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_PDF)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+    return EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)

tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_001431_case5.py

@@ -0,0 +1,122 @@
+"""Mapper-driven cascade pin against the Elmhurst P960-0001-001431
+"simulated case 5" worksheet — a DETACHED, SANDSTONE-walled cousin of
+golden cert 0240 (Main + Extension + room-in-roof, age band J).
+
+Like the other 001431 cases, this fixture does NOT hand-build the
+EpcPropertyData: it routes the Summary PDF through
+ElmhurstSiteNotesExtractor + from_elmhurst_site_notes so the SAP-result
+pin grid exercises the WHOLE extractor + mapper + calculator pipeline.
+
+Purpose: prove the calculator is spec-correct for a DETACHED room-in-roof
+with one Exposed + one Party gable, validating S0380.196 (API Simplified
+Type 1 RR gables deduct from the A_RR shell) against a real worksheet.
+The worksheet prints the exact routing the cascade implements:
+
+  Roof room Main Gable Wall 1  15.68  U=0.35  (29a)  ← Exposed → walls @ main-wall U
+  Roof room Main remaining area 61.73  U=0.30  (30)  ← A_RR shell − Σ gables (residual)
+  External roof Main           14.52  U=0.11  (30)  ← loft residual
+  Roof room Main Gable Wall 2  15.68  U=0.25  (32)  ← Party → party @ 0.25
+
+gable area = 6.40 × 2.45 = 15.68 m² (the §3.9.1 default RR storey height).
+A_RR remaining = 12.5√(83.2/1.5) − 2×15.68 = 93.09 − 31.36 = 61.73.
+
+This case surfaced two extractor/mapper gaps fixed in the same slice
+(S0380.197):
+- the sandstone wall label "SS Stone: sandstone or limestone" had no
+  `_ELMHURST_WALL_CODE_TO_SAP10` entry (→ WALL_STONE_SANDSTONE=2, matching
+  0240's API `wall_construction=2`);
+- the roof "Insulation Thickness 400+ mm" was silently dropped by the
+  extractor's `.split()[0].isdigit()` thickness parse (the trailing "+"),
+  so u_roof fell back to the age-J default 0.16 instead of 0.11
+  (`_parse_thickness_mm` now strips to leading digits).
+
+Cert shape: Detached house, Main + Extension 1, sandstone insulated walls,
+2 storeys + room-in-roof on the Main (floor 83.2 m², one Exposed + one
+Party gable, L=6.40 each), oil community/boiler (SAP code 901 combi route,
+control 2106), no PV, 20 low-energy lighting bulbs.
+
+Source: user-simulated PDFs at `sap worksheets/golden fixture
+debugging/simulated case 5/`. The Summary is mirrored into the tracked
+`backend/documents_parser/tests/fixtures/Summary_001431_case5.pdf`.
+
+Worksheet pin targets (P960-0001-001431, Block 1 — energy rating):
+- SAP rating 61 (line 258), ECF 2.7724 (line 257)
+- Total fuel cost £1586.4549 (line 255)
+- CO2 8387.6229 kg/year (line 272)
+- Space heating 12838.6489 kWh/year (Σ monthly (98))
+- Main 1 fuel 21397.7480 kWh/year (line 211)
+- Secondary fuel 0.0 (line 215)
+- Hot water fuel 6498.2518 kWh/year (line 219)
+- Lighting 381.4601 kWh/year (line 232)
+- Pumps/fans 141.0 kWh/year (line 231)
+
+Per [[feedback-zero-error-strict]] + [[feedback-e2e-validation-
+philosophy]]: pins are abs=1e-4 against the worksheet PDF.
+"""
+
+from __future__ import annotations
+
+import re
+import subprocess
+from pathlib import Path
+from typing import Final
+
+from backend.documents_parser.elmhurst_extractor import ElmhurstSiteNotesExtractor
+from datatypes.epc.domain.epc_property_data import EpcPropertyData
+from datatypes.epc.domain.mapper import EpcPropertyDataMapper
+
+
+# parents[0]=worksheet/, [1]=sap10_calculator/, [2]=domain/, [3]=tests/,
+# [4]=repo root.
+_SUMMARY_PDF: Final[Path] = (
+    Path(__file__).resolve().parents[4]
+    / "backend" / "documents_parser" / "tests" / "fixtures"
+    / "Summary_001431_case5.pdf"
+)
+
+
+def _summary_pdf_to_textract_style_pages(pdf_path: Path) -> list[str]:
+    """Convert a Summary PDF into the per-page text format the
+    ElmhurstSiteNotesExtractor expects (label\\nvalue sequences).
+
+    Mirror of the helper in `test_summary_pdf_mapper_chain.py` /
+    `_elmhurst_worksheet_000565.py`.
+    """
+    info = subprocess.run(
+        ["pdfinfo", str(pdf_path)], capture_output=True, text=True, check=True,
+    ).stdout
+    m = re.search(r"Pages:\s+(\d+)", info)
+    if m is None:
+        raise RuntimeError(f"Could not parse page count from {pdf_path}")
+    page_count = int(m.group(1))
+
+    pages: list[str] = []
+    for i in range(1, page_count + 1):
+        layout = subprocess.run(
+            [
+                "pdftotext", "-layout", "-f", str(i), "-l", str(i),
+                str(pdf_path), "-",
+            ],
+            capture_output=True, text=True, check=True,
+        ).stdout
+        tokens: list[str] = []
+        for line in layout.splitlines():
+            if not line.strip():
+                tokens.append("")
+                continue
+            parts = [p for p in re.split(r"\s{2,}", line.strip()) if p]
+            tokens.extend(parts)
+        pages.append("\n".join(tokens))
+    return pages
+
+
+def build_epc() -> EpcPropertyData:
+    """Route the simulated case-5 Summary through extractor + mapper.
+
+    No hand-built EpcPropertyData — the extractor and mapper are part of
+    the test target. Exercises the S0380.196 RR-gable deduction, the
+    S0380.197 sandstone-wall-label + "400+ mm" roof-thickness fixes.
+    """
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_PDF)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+    return EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)

tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_001431_case6.py

@@ -0,0 +1,156 @@
+"""Mapper-driven cascade fixture for the Elmhurst P960-0001-001431
+"simulated case 6" worksheet — a DETACHED, dual-oil cousin of golden
+cert 0240 carrying ROOM-IN-ROOF WINDOWS (rooflights).
+
+Routes the Summary PDF through ElmhurstSiteNotesExtractor +
+from_elmhurst_site_notes (no hand-built EpcPropertyData) so the pin
+exercises the whole extractor + mapper + calculator pipeline.
+
+Purpose: validate S0380.198/199 ROOF-WINDOW handling against a real
+worksheet. Case 6 lodges 6 windows on the room-in-roof ("Roof of Room"
+location); the worksheet bills them on line (27a) Roof Windows at
+U_eff 2.1062 (= inclined 2.30 with the §3.2 R=0.04 curtain transform),
+NOT on (27) as vertical glazing. This is the site-notes mirror of
+0240's API `window_wall_type=4` roof windows (S0380.198).
+
+This cert surfaced two site-notes gaps fixed in S0380.199:
+- the extractor mangled the "Roof of Room in Roof" window-location cell
+  into the glazing-type phrase ("Double between 2002 Roof of Room and
+  2021 in Roof" → UnmappedElmhurstLabel); `_parse_window_from_anchors`
+  now detects + strips those tokens and marks the window roof-of-room;
+- `_is_elmhurst_roof_window` gained a "Roof of Room" location branch,
+  and `_ELMHURST_ROOF_WINDOW_U_BY_GLAZING` an entry for the
+  already-inclined "Double between 2002 and 2021" → 2.30 (so the
+  inclination adjustment isn't double-applied).
+
+SCOPE: promoted to a FULL SapResult e2e fixture (S0380.207) once the dual
+main heating system was fully modelled. Case 6 has Main 1 radiators (51%,
+control 2106) + Main 2 underfloor (49%, control 2110) heating different
+parts. Closing every line ref took: Table 4f note c) two circulation
+pumps (231) S0380.201; Table 5a note a) two pump gains (70) S0380.202;
+RdSAP §3.7 "Roof of Room" rooflights → §3.10.1 RR residual (30) S0380.203;
+SAP 10.2 p.186 two-systems-different-parts MIT — weighted responsiveness
+0.8775 + elsewhere two-control blend — (87)/(90)/(98c) S0380.205 (with
+the Main 2 emitter/control extractor fix S0380.204); and Eq D1 per-boiler
+(204) space share (219) S0380.206. SapResult pins (Block 1 energy rating)
+live in `test_e2e_elmhurst_sap_score.py::_FIXTURE_PINS["001431_case6"]`;
+`main_heating_fuel_kwh_per_yr` is the (211)+(213) two-system sum. Heating
+is SAP code 127 (vs 0240's 130 condensing combi) — case 6 pins to its OWN
+worksheet, the spec authority for this dual-oil archetype.
+
+The §3 window line refs (27)/(27a)/(31), the roof (30), the pumps (231),
+the pump gains (70), the per-system fuel (211)/(213), and HW (219) also
+have dedicated section pins in `test_section_cascade_pins.py`.
+
+Source: user-simulated PDFs at `sap worksheets/golden fixture
+debugging/simulated case 6/`. Summary mirrored into the tracked
+`backend/documents_parser/tests/fixtures/Summary_001431_case6.pdf`.
+
+Worksheet §3 window pin targets (P960-0001-001431, Block 1):
+- (27)  Windows       = 19.3704 (Main) + 3.3704 (Ext1) = 22.7408 W/K
+- (27a) Roof Windows  = 6.19 m² × 2.1062 = 13.0375 W/K  (the 6 rooflights)
+- (31)  Total external element area = 336.13 m²
+
+Per [[feedback-zero-error-strict]]: pins are abs=1e-4 against the PDF.
+"""
+
+from __future__ import annotations
+
+import re
+import subprocess
+from pathlib import Path
+from typing import Final
+
+from backend.documents_parser.elmhurst_extractor import ElmhurstSiteNotesExtractor
+from datatypes.epc.domain.epc_property_data import EpcPropertyData
+from datatypes.epc.domain.mapper import EpcPropertyDataMapper
+
+
+# parents[0]=worksheet/, [1]=sap10_calculator/, [2]=domain/, [3]=tests/,
+# [4]=repo root.
+_SUMMARY_PDF: Final[Path] = (
+    Path(__file__).resolve().parents[4]
+    / "backend" / "documents_parser" / "tests" / "fixtures"
+    / "Summary_001431_case6.pdf"
+)
+
+# Worksheet §3 window line refs (Block 1 — energy rating).
+LINE_27_WINDOWS_W_PER_K: Final[float] = 22.7408
+LINE_27A_ROOF_WINDOWS_W_PER_K: Final[float] = 13.0375
+LINE_31_TOTAL_EXTERNAL_AREA_M2: Final[float] = 336.13
+
+# Worksheet (30) Roof total W/K = RR remaining (net of the 6.19 m² roof
+# windows) 55.54 × 0.30 = 16.6620 + External roof Main 14.52 × 0.11 =
+# 1.5972 + External roof Ext1 7.21 × 0.11 = 0.7931 → 19.0523. The 6 "Roof
+# of Room" rooflights pierce the room-in-roof sloped ceiling, so their
+# area deducts from the RR residual area, NOT the external flat roof.
+LINE_30_ROOF_W_PER_K: Final[float] = 19.0523
+
+# Worksheet (231) "Total electricity for the above, kWh/year" (Block 1).
+# Decomposes as (230c) central heating pump 156 + (230d) oil boiler pump
+# 200. (230c) = 41 (Main 1 circ pump, "2013 or later") + 115 (Main 2 circ
+# pump, unknown date) — the two-main-system circulation-pump pair per
+# SAP 10.2 Table 4f note c. (230d) = 2 × 100 oil-boiler aux (already
+# wired in `_table_4f_additive_components`).
+LINE_231_PUMPS_FANS_KWH: Final[float] = 356.0
+
+# Worksheet (211)/(213) per-system space-heating fuel (kWh/yr). The dual
+# oil boiler heats different parts (Main 1 radiators/2106 living 51%, Main
+# 2 underfloor/2110 elsewhere 49%) — the SAP 10.2 p.186 two-systems-
+# different-parts MIT (weighted R 0.8775 + elsewhere two-control blend)
+# lands (98c) demand 11991.96 exact, so the per-system fuels pin.
+LINE_211_MAIN_1_FUEL_KWH: Final[float] = 7741.6458
+LINE_213_MAIN_2_FUEL_KWH: Final[float] = 6995.3106
+
+# Worksheet (219) water-heating fuel (kWh/yr). The DHW boiler is Main 1
+# (WHC 901), which provides only 51% of space heating, so SAP 10.2
+# Appendix D Eq D1 weights η_winter by Main 1's (204) share — not the
+# dwelling total — when blending the monthly water-heater efficiency.
+LINE_219_HOT_WATER_FUEL_KWH: Final[float] = 4902.8601
+
+# Worksheet (70) "Pumps, fans" internal-gain (W), heating-season only
+# (Jun-Sep = 0). = 10 W = the two-main-system central-heating-pump pair
+# per SAP 10.2 Table 5a note a): Main 1 ("2013 or later" → 3 W) + Main 2
+# (unknown date → 7 W). The pre-S0380.202 cascade billed a single Main 1
+# pump (3 W).
+LINE_70_PUMPS_FANS_GAINS_W: Final[tuple[float, ...]] = (
+    10.0, 10.0, 10.0, 10.0, 10.0, 0.0, 0.0, 0.0, 0.0, 10.0, 10.0, 10.0,
+)
+
+
+def _summary_pdf_to_textract_style_pages(pdf_path: Path) -> list[str]:
+    """Convert a Summary PDF into the per-page text format the
+    ElmhurstSiteNotesExtractor expects (mirror of the case-5 helper)."""
+    info = subprocess.run(
+        ["pdfinfo", str(pdf_path)], capture_output=True, text=True, check=True,
+    ).stdout
+    m = re.search(r"Pages:\s+(\d+)", info)
+    if m is None:
+        raise RuntimeError(f"Could not parse page count from {pdf_path}")
+    page_count = int(m.group(1))
+
+    pages: list[str] = []
+    for i in range(1, page_count + 1):
+        layout = subprocess.run(
+            [
+                "pdftotext", "-layout", "-f", str(i), "-l", str(i),
+                str(pdf_path), "-",
+            ],
+            capture_output=True, text=True, check=True,
+        ).stdout
+        tokens: list[str] = []
+        for line in layout.splitlines():
+            if not line.strip():
+                tokens.append("")
+                continue
+            parts = [p for p in re.split(r"\s{2,}", line.strip()) if p]
+            tokens.extend(parts)
+        pages.append("\n".join(tokens))
+    return pages
+
+
+def build_epc() -> EpcPropertyData:
+    """Route the simulated case-6 Summary through extractor + mapper."""
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_PDF)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+    return EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)

tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_001431_case7.py

@@ -0,0 +1,134 @@
+"""Mapper-driven cascade fixture for the Elmhurst P960-0001-001431
+"simulated case 7" worksheet — the CONDENSING-OIL-COMBI variant of
+[[case 6]], generated to validate the combi HW + space efficiency path
+that golden cert 0240-0200-5706-2365-8010 exercises.
+
+Routes the Summary PDF through ElmhurstSiteNotesExtractor +
+from_elmhurst_site_notes (no hand-built EpcPropertyData) so the pin
+exercises the whole extractor + mapper + calculator pipeline.
+
+WHY THIS FIXTURE EXISTS
+-----------------------
+Case 6 is SAP code 127 ("Condensing oil *boiler*", regular) + a 110 L
+cylinder — so it never exercised the COMBI instantaneous-DHW efficiency
+path. 0240 is SAP code 130 ("Condensing combi oil boiler") with NO
+cylinder. Case 7 is case 6 with that single difference swapped in:
+
+  - both mains → SAP code 130 (Table 4b winter 82 / summer 73);
+  - NO hot-water cylinder → combi instantaneous DHW (WHC 901), Table 3a
+    keep-hot combi loss (61), no primary/storage loss;
+  - boiler interlock PRESENT (combi + room thermostat 2106, no cylinder)
+    → NO −5pp penalty, base eff 82/73 — the OPPOSITE of case 6.
+
+The dual-main rads(2106, 51%) + UFH(2110, 49%) different-parts structure,
+the 6 "Roof of Room" rooflights, and the fabric are unchanged from case 6.
+
+WHAT IT PROVED
+--------------
+The cascade reproduces the case-7 worksheet EXACTLY at abs=1e-4 on every
+top-level output with ZERO calculator changes — the condensing-combi
+(130) + no-cylinder + dual-main + Appendix D Eq D1 path is already
+correct. This fixture is a regression lock on that path; it did NOT
+require a fix. (It also exonerates the combi mechanism as the source of
+0240's API-path residual — see docs/HANDOVER_0240_CLOSURE.md.)
+
+Combi-path worksheet line refs (P960-0001-001431, Block 1):
+- (206)/(207) main space-heating efficiency = 82.0000 / 82.0000 (base,
+  interlock present, no −5pp).
+- (216)   water-heater efficiency (summer base) = 73.0000.
+- (217)m  water-heater monthly efficiency = combi blend 73.00 → 80.18.
+- (61)m   combi loss = 50.9589 (Jan) … = 600 kWh/yr flat (Table 3a
+  keep-hot, daily HW volume > 100 L every month so the "no keep-hot"
+  fu-scaling collapses to 1.0).
+- (59)m   primary loss = 0 and storage loss = 0 (combi, no cylinder).
+- (211)   space-heating fuel main 1 = 7865.4304.
+- (213)   space-heating fuel main 2 = 7556.9821.
+- (219)   water-heating fuel = 3496.8121.
+- (64)    HW demand total = 2712.0619 (smaller dwelling than 0240's
+  2842.82 — case 7 validates the combi *mechanism*, not 0240's absolute
+  demand).
+
+Per [[feedback-zero-error-strict]]: e2e pins are abs=1e-4 against the PDF
+(see test_e2e_elmhurst_sap_score.py::_FIXTURE_PINS["001431_case7"]).
+
+Source: user-simulated PDFs at `sap worksheets/golden fixture
+debugging/simulated case 7/`. Summary mirrored into the tracked
+`backend/documents_parser/tests/fixtures/Summary_001431_case7.pdf`.
+"""
+
+from __future__ import annotations
+
+import re
+import subprocess
+from pathlib import Path
+from typing import Final
+
+from backend.documents_parser.elmhurst_extractor import ElmhurstSiteNotesExtractor
+from datatypes.epc.domain.epc_property_data import EpcPropertyData
+from datatypes.epc.domain.mapper import EpcPropertyDataMapper
+
+# parents[0]=worksheet/, [1]=sap10_calculator/, [2]=domain/, [3]=tests/,
+# [4]=repo root.
+_SUMMARY_PDF: Final[Path] = (
+    Path(__file__).resolve().parents[4]
+    / "backend" / "documents_parser" / "tests" / "fixtures"
+    / "Summary_001431_case7.pdf"
+)
+
+# Worksheet (211)/(213) per-system space-heating fuel (kWh/yr). Both mains
+# are condensing oil combis (SAP code 130, Table 4b 82/73) at base
+# efficiency — interlock present (combi + room thermostat, no cylinder),
+# so NO −5pp penalty (the case-6 boiler+cylinder had no cylinder stat → a
+# −5pp penalty; the combi removes it).
+LINE_211_MAIN_1_FUEL_KWH: Final[float] = 7865.4304
+LINE_213_MAIN_2_FUEL_KWH: Final[float] = 7556.9821
+
+# Worksheet (219) water-heating fuel (kWh/yr). Combi instantaneous DHW
+# (WHC 901) — SAP 10.2 Appendix D Eq D1 blends the monthly water-heater
+# efficiency (217)m by the DHW boiler's (204) space share; Table 3a
+# keep-hot combi loss (61) = 600 kWh/yr; no primary/storage loss.
+LINE_219_HOT_WATER_FUEL_KWH: Final[float] = 3496.8121
+
+# Worksheet (206)/(207) main space-heating efficiency — base 82, no
+# −5pp (interlock present). Watch these if the pin ever regresses: a
+# silent interlock flip drops them to 77/68.
+LINE_206_MAIN_1_EFFICIENCY_PCT: Final[float] = 82.0
+LINE_207_MAIN_2_EFFICIENCY_PCT: Final[float] = 82.0
+
+
+def _summary_pdf_to_textract_style_pages(pdf_path: Path) -> list[str]:
+    """Convert a Summary PDF into the per-page text format the
+    ElmhurstSiteNotesExtractor expects (mirror of the case-6 helper)."""
+    info = subprocess.run(
+        ["pdfinfo", str(pdf_path)], capture_output=True, text=True, check=True,
+    ).stdout
+    m = re.search(r"Pages:\s+(\d+)", info)
+    if m is None:
+        raise RuntimeError(f"Could not parse page count from {pdf_path}")
+    page_count = int(m.group(1))
+
+    pages: list[str] = []
+    for i in range(1, page_count + 1):
+        layout = subprocess.run(
+            [
+                "pdftotext", "-layout", "-f", str(i), "-l", str(i),
+                str(pdf_path), "-",
+            ],
+            capture_output=True, text=True, check=True,
+        ).stdout
+        tokens: list[str] = []
+        for line in layout.splitlines():
+            if not line.strip():
+                tokens.append("")
+                continue
+            parts = [p for p in re.split(r"\s{2,}", line.strip()) if p]
+            tokens.extend(parts)
+        pages.append("\n".join(tokens))
+    return pages
+
+
+def build_epc() -> EpcPropertyData:
+    """Route the simulated case-7 Summary through extractor + mapper."""
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_PDF)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+    return EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)

tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_001431_rr.py

@@ -0,0 +1,124 @@
+"""Mapper-driven cascade pin against the Elmhurst P960-0001-001431
+"simulated case 2" worksheet — a Main + Extension dwelling with a
+Simplified room-in-roof (the 6035 archetype, more complete than sim
+case 1).
+
+Like 000565 / sim case 1, this fixture does NOT hand-build the
+EpcPropertyData: it routes the Summary PDF through
+ElmhurstSiteNotesExtractor + from_elmhurst_site_notes so the SAP-result
+pin grid exercises the WHOLE extractor + mapper + calculator pipeline.
+
+This cert surfaced two real cascade bugs (both fixed; this fixture pins
+them end-to-end at 1e-4):
+
+  S0380.192 — Simplified room-in-roof. The Summary lodges placeholder
+    slope/ceiling Length/Height cells (a 40 m ceiling height, a 32 m
+    slope on a 4.65 m gable). RdSAP 10 §3.9.1 derives one timber-framed
+    "remaining area" from the floor area instead
+    (A_RR = 12.5√(A_floor/1.5) − Σgables = 32.89 m²). Emitting the
+    placeholders as detailed_surfaces billed 1024 + 160 m² of explicit
+    roof area → a 7.5× fabric-heat-loss explosion (SAP −14.6). Fixed by
+    dropping roof-going surfaces for Simplified assessments so the
+    cascade's residual formula fires.
+
+  S0380.193 — Suspended-timber-floor "sealed/unsealed" infiltration.
+    RdSAP 10 §5 (PDF p.29) line (12): rule (a) ("U-value < 0.5 → sealed
+    0.1") applies only when a floor U-value is SUPPLIED. This cert's
+    floor is as-built/uninsulated (default U=0.43, not supplied), so it
+    falls to rule (b) → unsealed 0.2. The cascade was feeding the
+    computed default U into rule (a) → sealed 0.1 → (25) effective ACH
+    dropped → space heating understated ~450 kWh.
+
+Source: user-simulated PDFs at `sap worksheets/golden fixture
+debugging/simulated case 2/`. The Summary is mirrored into the tracked
+`backend/documents_parser/tests/fixtures/Summary_001431_rr_ext.pdf`
+(distinct name — the corpus reuses cert 001431; sim case 1 is the
+single-part gas-combi variant) so the test runs without depending on
+the unstaged workspace.
+
+Cert shape: Main + Extension 1, both solid brick WITH internal
+insulation (Main) / as-built (Ext1), 3 storeys, Simplified room-in-roof
+on the Main (floor 29.75 m², exposed + party gables), suspended
+uninsulated ground floors, gas-combi SAP code 104, no PV.
+
+Worksheet pin targets (P960-0001-001431, Block 1 — energy rating):
+- SAP rating 69 (line 258), ECF 2.2395 (line 257)
+- Total fuel cost £920.5046 (line 255)
+- CO2 4566.7090 kg/year (line 272)
+- Space heating 15269.8593 kWh/year (Σ monthly (98))
+- Main 1 fuel 18178.4039 kWh/year (line 211)
+- Secondary fuel 0.0 (line 215)
+- Hot water fuel 3308.6172 kWh/year (line 219)
+- Lighting 282.6414 kWh/year (line 232)
+- Pumps/fans 86.0 kWh/year (line 231)
+
+Per [[feedback-zero-error-strict]] + [[feedback-e2e-validation-
+philosophy]]: pins are abs=1e-4 against the worksheet PDF.
+"""
+
+from __future__ import annotations
+
+import re
+import subprocess
+from pathlib import Path
+from typing import Final
+
+from backend.documents_parser.elmhurst_extractor import ElmhurstSiteNotesExtractor
+from datatypes.epc.domain.epc_property_data import EpcPropertyData
+from datatypes.epc.domain.mapper import EpcPropertyDataMapper
+
+
+# parents[0]=worksheet/, [1]=sap10_calculator/, [2]=domain/, [3]=tests/,
+# [4]=repo root.
+_SUMMARY_PDF: Final[Path] = (
+    Path(__file__).resolve().parents[4]
+    / "backend" / "documents_parser" / "tests" / "fixtures"
+    / "Summary_001431_rr_ext.pdf"
+)
+
+
+def _summary_pdf_to_textract_style_pages(pdf_path: Path) -> list[str]:
+    """Convert a Summary PDF into the per-page text format the
+    ElmhurstSiteNotesExtractor expects (label\\nvalue sequences).
+
+    Mirror of the helper in `test_summary_pdf_mapper_chain.py` /
+    `_elmhurst_worksheet_000565.py`.
+    """
+    info = subprocess.run(
+        ["pdfinfo", str(pdf_path)], capture_output=True, text=True, check=True,
+    ).stdout
+    m = re.search(r"Pages:\s+(\d+)", info)
+    if m is None:
+        raise RuntimeError(f"Could not parse page count from {pdf_path}")
+    page_count = int(m.group(1))
+
+    pages: list[str] = []
+    for i in range(1, page_count + 1):
+        layout = subprocess.run(
+            [
+                "pdftotext", "-layout", "-f", str(i), "-l", str(i),
+                str(pdf_path), "-",
+            ],
+            capture_output=True, text=True, check=True,
+        ).stdout
+        tokens: list[str] = []
+        for line in layout.splitlines():
+            if not line.strip():
+                tokens.append("")
+                continue
+            parts = [p for p in re.split(r"\s{2,}", line.strip()) if p]
+            tokens.extend(parts)
+        pages.append("\n".join(tokens))
+    return pages
+
+
+def build_epc() -> EpcPropertyData:
+    """Route the simulated case-2 Summary through extractor + mapper.
+
+    No hand-built EpcPropertyData — the extractor and mapper are part of
+    the test target. Exercises the S0380.192 Simplified-RR fix and the
+    S0380.193 suspended-floor sealed-rule fix.
+    """
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_PDF)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+    return EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)

tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_001431_rr8.py

@@ -0,0 +1,112 @@
+"""Mapper-driven cascade pin against the Elmhurst P960-0001-001431
+"simulated case 3" worksheet — a near-exact replica of golden cert
+6035 (Main + Extension + Simplified room-in-roof, 8 windows).
+
+Like 000565 / sim case 1 / sim case 2, this fixture does NOT hand-build
+the EpcPropertyData: it routes the Summary PDF through
+ElmhurstSiteNotesExtractor + from_elmhurst_site_notes so the SAP-result
+pin grid exercises the WHOLE extractor + mapper + calculator pipeline.
+
+Purpose: prove the calculator is spec-correct for the 6035 archetype
+(after S0380.192 Simplified-RR + S0380.193 suspended-floor fixes). This
+cert reproduces 6035's 8 windows (≈14.15 m²) and Main ground-floor
+heat-loss perimeter (15.99 m). It still differs from 6035 in ONE input:
+the Main FIRST-floor HLP is 15.99 here vs 6035's 8.32 (6035's upper
+storey has less exposed perimeter), so it is not yet byte-identical to
+6035. All 11 Block-1 line refs nonetheless pin at abs=1e-4 against this
+cert's OWN worksheet, confirming the cascade reproduces the spec engine
+exactly for this Main+Ext+RR+suspended-floor+gas-combi shape — so 6035's
+residual +19 PE vs the lodged register is lodged-register divergence,
+not a cascade gap.
+
+Cert shape: Main + Extension 1, both solid brick WITH internal
+insulation (Main) / as-built (Ext1), 3 storeys, Simplified room-in-roof
+on the Main (floor 29.75 m², exposed + party gables), suspended
+uninsulated ground floors, gas-combi SAP code 104, 8 windows, no PV.
+
+Source: user-simulated PDFs at `sap worksheets/golden fixture
+debugging/simulated case 3/`. The Summary is mirrored into the tracked
+`backend/documents_parser/tests/fixtures/Summary_001431_rr8w.pdf`
+(distinct name — the corpus reuses cert 001431).
+
+Worksheet pin targets (P960-0001-001431, Block 1 — energy rating):
+- SAP rating 68 (line 258), ECF 2.3146 (line 257)
+- Total fuel cost £951.3425 (line 255)
+- CO2 4767.4862 kg/year (line 272)
+- Space heating 16086.3557 kWh/year (Σ monthly (98))
+- Main 1 fuel 19150.4235 kWh/year (line 211)
+- Secondary fuel 0.0 (line 215)
+- Hot water fuel 3307.2639 kWh/year (line 219)
+- Lighting 262.0885 kWh/year (line 232)
+- Pumps/fans 86.0 kWh/year (line 231)
+
+Per [[feedback-zero-error-strict]] + [[feedback-e2e-validation-
+philosophy]]: pins are abs=1e-4 against the worksheet PDF.
+"""
+
+from __future__ import annotations
+
+import re
+import subprocess
+from pathlib import Path
+from typing import Final
+
+from backend.documents_parser.elmhurst_extractor import ElmhurstSiteNotesExtractor
+from datatypes.epc.domain.epc_property_data import EpcPropertyData
+from datatypes.epc.domain.mapper import EpcPropertyDataMapper
+
+
+# parents[0]=worksheet/, [1]=sap10_calculator/, [2]=domain/, [3]=tests/,
+# [4]=repo root.
+_SUMMARY_PDF: Final[Path] = (
+    Path(__file__).resolve().parents[4]
+    / "backend" / "documents_parser" / "tests" / "fixtures"
+    / "Summary_001431_rr8w.pdf"
+)
+
+
+def _summary_pdf_to_textract_style_pages(pdf_path: Path) -> list[str]:
+    """Convert a Summary PDF into the per-page text format the
+    ElmhurstSiteNotesExtractor expects (label\\nvalue sequences).
+
+    Mirror of the helper in `test_summary_pdf_mapper_chain.py` /
+    `_elmhurst_worksheet_000565.py`.
+    """
+    info = subprocess.run(
+        ["pdfinfo", str(pdf_path)], capture_output=True, text=True, check=True,
+    ).stdout
+    m = re.search(r"Pages:\s+(\d+)", info)
+    if m is None:
+        raise RuntimeError(f"Could not parse page count from {pdf_path}")
+    page_count = int(m.group(1))
+
+    pages: list[str] = []
+    for i in range(1, page_count + 1):
+        layout = subprocess.run(
+            [
+                "pdftotext", "-layout", "-f", str(i), "-l", str(i),
+                str(pdf_path), "-",
+            ],
+            capture_output=True, text=True, check=True,
+        ).stdout
+        tokens: list[str] = []
+        for line in layout.splitlines():
+            if not line.strip():
+                tokens.append("")
+                continue
+            parts = [p for p in re.split(r"\s{2,}", line.strip()) if p]
+            tokens.extend(parts)
+        pages.append("\n".join(tokens))
+    return pages
+
+
+def build_epc() -> EpcPropertyData:
+    """Route the simulated case-2 Summary through extractor + mapper.
+
+    No hand-built EpcPropertyData — the extractor and mapper are part of
+    the test target. Exercises the S0380.192 Simplified-RR fix and the
+    S0380.193 suspended-floor sealed-rule fix.
+    """
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_PDF)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+    return EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)

tests/domain/sap10_calculator/worksheet/test_e2e_elmhurst_sap_score.py

@@ -38,6 +38,12 @@ from tests.domain.sap10_calculator.worksheet import (
     _elmhurst_worksheet_000516 as _w000516,
     _elmhurst_worksheet_000565 as _w000565,
     _elmhurst_worksheet_001431 as _w001431,
+    _elmhurst_worksheet_001431_rr as _w001431_rr,
+    _elmhurst_worksheet_001431_rr8 as _w001431_rr8,
+    _elmhurst_worksheet_001431_6035 as _w001431_6035,
+    _elmhurst_worksheet_001431_case5 as _w001431_case5,
+    _elmhurst_worksheet_001431_case6 as _w001431_case6,
+    _elmhurst_worksheet_001431_case7 as _w001431_case7,
 )
 from tests.domain.sap10_calculator.worksheet._elmhurst_fixtures import (
     ALL_FIXTURES as _ELMHURST_FIXTURES,
@@ -167,6 +173,111 @@ _FIXTURE_PINS: Final[dict[str, FixtureCascadePins]] = {
         lighting_kwh_per_yr=283.2229,
         pumps_fans_kwh_per_yr=86.0,
     ),
+    # Mapper-driven cohort entry — Summary_001431_rr_ext.pdf → extractor
+    # → mapper → calculator. Main + Extension, Simplified room-in-roof,
+    # suspended uninsulated floors (the 6035 archetype). Surfaced + pins
+    # S0380.192 (Simplified-RR remaining area) and S0380.193 (suspended-
+    # floor sealed/unsealed rule). Pins are worksheet Block 1 line refs.
+    "001431_rr": FixtureCascadePins(
+        sap_score=69, sap_score_continuous=68.7584, ecf=2.2395,
+        total_fuel_cost_gbp=920.5046, co2_kg_per_yr=4566.7090,
+        space_heating_kwh_per_yr=15269.8593,
+        main_heating_fuel_kwh_per_yr=18178.4039,
+        secondary_heating_fuel_kwh_per_yr=0.0,
+        hot_water_kwh_per_yr=3308.6172,
+        lighting_kwh_per_yr=282.6414,
+        pumps_fans_kwh_per_yr=86.0,
+    ),
+    # Mapper-driven cohort entry — Summary_001431_rr8w.pdf → extractor →
+    # mapper → calculator. Near-exact 6035 replica: Main + Extension +
+    # Simplified room-in-roof, 8 windows (≈14.15 m², matching 6035),
+    # suspended uninsulated floors. Differs from 6035 only in the Main
+    # first-floor HLP (15.99 here vs 6035's 8.32). Pins at 1e-4 confirm
+    # the cascade is spec-correct for the archetype → 6035's +19 PE vs
+    # the lodged register is lodged-register divergence, not a calc gap.
+    "001431_rr8": FixtureCascadePins(
+        sap_score=68, sap_score_continuous=67.7118, ecf=2.3146,
+        total_fuel_cost_gbp=951.3425, co2_kg_per_yr=4767.4862,
+        space_heating_kwh_per_yr=16086.3557,
+        main_heating_fuel_kwh_per_yr=19150.4235,
+        secondary_heating_fuel_kwh_per_yr=0.0,
+        hot_water_kwh_per_yr=3307.2639,
+        lighting_kwh_per_yr=262.0885,
+        pumps_fans_kwh_per_yr=86.0,
+    ),
+    # Mapper-driven cohort entry — Summary_001431_6035.pdf → extractor →
+    # mapper → calculator. Reproduces 6035's full floor geometry (Main
+    # ground HLP 15.99 + first 8.32, asymmetric) and 8 windows. Residual
+    # vs 6035 is two lodged inputs only (largest window orientation,
+    # meter type). Pins at 1e-4 → 6035's +19 PE is lodged divergence.
+    "001431_6035": FixtureCascadePins(
+        sap_score=68, sap_score_continuous=68.1906, ecf=2.2802,
+        total_fuel_cost_gbp=937.2341, co2_kg_per_yr=4682.3494,
+        space_heating_kwh_per_yr=15745.3260,
+        main_heating_fuel_kwh_per_yr=18744.4357,
+        secondary_heating_fuel_kwh_per_yr=0.0,
+        hot_water_kwh_per_yr=3307.8383,
+        lighting_kwh_per_yr=262.0885,
+        pumps_fans_kwh_per_yr=86.0,
+    ),
+    # Mapper-driven cohort entry — Summary_001431_case5.pdf → extractor →
+    # mapper → calculator. DETACHED, SANDSTONE-walled cousin of cert 0240:
+    # Main + Extension + room-in-roof (floor 83.2 m², one Exposed + one
+    # Party gable L=6.40), age J, oil combi (SAP 901), no PV. Validates
+    # S0380.196 (RR gable deduction) against a real worksheet — the
+    # worksheet prints Gable 1 (Exposed) at (29a) U=0.35, Gable 2 (Party)
+    # at (32) U=0.25, remaining area = shell − Σ gables at (30). Also pins
+    # the S0380.197 sandstone "SS" wall label + "400+ mm" roof-thickness
+    # extractor fixes (without the latter, roof U fell to 0.16 not 0.11).
+    "001431_case5": FixtureCascadePins(
+        sap_score=61, sap_score_continuous=61.3255, ecf=2.7724,
+        total_fuel_cost_gbp=1586.4549, co2_kg_per_yr=8387.6229,
+        space_heating_kwh_per_yr=12838.6489,
+        main_heating_fuel_kwh_per_yr=21397.7480,
+        secondary_heating_fuel_kwh_per_yr=0.0,
+        hot_water_kwh_per_yr=6498.2518,
+        lighting_kwh_per_yr=381.4601,
+        pumps_fans_kwh_per_yr=141.0,
+    ),
+    # Mapper-driven cohort entry — Summary_001431_case6.pdf → extractor →
+    # mapper → calculator. DETACHED dual-oil cousin of case 5: Main 1
+    # radiators (control 2106) + Main 2 underfloor (control 2110) heating
+    # DIFFERENT parts (51% / 49%), 6 "Roof of Room" rooflights, no boiler
+    # interlock (cyl stat No → −5pp on Main 1). Promoted to a full
+    # SapResult fixture once S0380.201-206 closed every line ref: Table 4f
+    # note c) two-pump electricity (231), Table 5a note a) two-pump gain
+    # (70), §3.7 rooflight→RR-residual (30), SAP 10.2 p.186 two-systems-
+    # different-parts MIT (87)/(90)/(98c), and Eq D1 per-boiler (204)
+    # space share (219). Pins are worksheet Block 1 (energy rating) line
+    # refs; main_heating_fuel_kwh_per_yr is the (211)+(213) two-system sum.
+    "001431_case6": FixtureCascadePins(
+        sap_score=72, sap_score_continuous=71.6597, ecf=2.0316,
+        total_fuel_cost_gbp=1162.5374, co2_kg_per_yr=5953.6679,
+        space_heating_kwh_per_yr=11991.9611,
+        main_heating_fuel_kwh_per_yr=14736.9564,
+        secondary_heating_fuel_kwh_per_yr=0.0,
+        hot_water_kwh_per_yr=4902.8601,
+        lighting_kwh_per_yr=357.6571,
+        pumps_fans_kwh_per_yr=356.0,
+    ),
+    # Mapper-driven cohort entry — Summary_001431_case7.pdf → extractor →
+    # mapper → calculator. Case 6 with the heating swapped to a CONDENSING
+    # OIL COMBI (SAP code 130, Table 4b 82/73) with NO cylinder — combi
+    # instantaneous DHW (WHC 901), Table 3a keep-hot combi loss (61), no
+    # primary/storage loss, boiler interlock PRESENT (no −5pp). Validates
+    # the combi HW + space efficiency path that golden cert 0240 uses;
+    # reproduces every line ref EXACTLY with no calculator change.
+    # main_heating_fuel_kwh_per_yr is the (211)+(213) two-system sum.
+    "001431_case7": FixtureCascadePins(
+        sap_score=73, sap_score_continuous=72.6153, ecf=1.9631,
+        total_fuel_cost_gbp=1123.3372, co2_kg_per_yr=5738.9315,
+        space_heating_kwh_per_yr=12646.3783,
+        main_heating_fuel_kwh_per_yr=15422.4125,
+        secondary_heating_fuel_kwh_per_yr=0.0,
+        hot_water_kwh_per_yr=3496.8121,
+        lighting_kwh_per_yr=357.6571,
+        pumps_fans_kwh_per_yr=356.0,
+    ),
 }
 
 
@@ -179,6 +290,12 @@ _FIXTURE_MODULES: Final[dict[str, ModuleType]] = {
     "000516": _w000516,
     "000565": _w000565,
     "001431": _w001431,
+    "001431_rr": _w001431_rr,
+    "001431_rr8": _w001431_rr8,
+    "001431_6035": _w001431_6035,
+    "001431_case5": _w001431_case5,
+    "001431_case6": _w001431_case6,
+    "001431_case7": _w001431_case7,
 }
 
 

tests/domain/sap10_calculator/worksheet/test_energy_requirements.py

@@ -60,6 +60,40 @@ def test_table_11_secondary_fraction_splits_q_heat_between_main_and_secondary()
     assert result.secondary_fuel_kwh_per_yr == 550.0
 
 
+def test_two_main_systems_split_q_heat_by_fraction_203_at_own_efficiencies() -> None:
+    """Spec §9a (203)/(204)/(205) two-main split: when a second main
+    system supplies (203) of the main heating, (204)=(202)×(1−(203)) goes
+    to system 1 at (206) and (205)=(202)×(203) to system 2 at (207). With
+    no secondary ((202)=1), (203)=0.49, eff1=79%, eff2=84%, Σ(98c)=4400:
+      Σ(211) = 4400 × 0.51 × 100/79 = 2840.5063 kWh
+      Σ(213) = 4400 × 0.49 × 100/84 = 2566.6667 kWh
+    Mirrors simulated case 6 (oil boiler, radiators 51% + underfloor 49%)
+    and cert 0240 (identical-efficiency systems collapse to the single-
+    main total)."""
+    # Arrange
+    monthly_space_heating = (
+        1000.0, 800.0, 600.0, 400.0, 200.0, 0.0,
+        0.0, 0.0, 0.0, 200.0, 400.0, 800.0,
+    )
+
+    # Act
+    result = space_heating_fuel_monthly_kwh(
+        space_heating_monthly_kwh=monthly_space_heating,
+        secondary_heating_fraction=0.0,
+        main_heating_efficiency_pct=79.0,
+        secondary_heating_efficiency_pct=0.0,
+        main_2_of_main_fraction=0.49,
+        main_2_efficiency_pct=84.0,
+    )
+
+    # Assert
+    assert abs(result.main_2_of_main_fraction - 0.49) <= 1e-12
+    assert abs(result.main_1_of_total_fraction - 0.51) <= 1e-12
+    assert abs(result.main_2_of_total_fraction - 0.49) <= 1e-12
+    assert abs(result.main_1_fuel_kwh_per_yr - 4400.0 * 0.51 * 100.0 / 79.0) <= 1e-9
+    assert abs(result.main_2_fuel_kwh_per_yr - 4400.0 * 0.49 * 100.0 / 84.0) <= 1e-9
+
+
 def test_per_month_fuel_preserves_summer_clamp_zeros_from_98c() -> None:
     """The §8 Table 9c summer clamp zeros (98c)m for Jun..Sep. §9a's per-
     month (211)m / (215)m tuples are linear in (98c)m so they inherit the

tests/domain/sap10_calculator/worksheet/test_heat_transmission.py

@@ -36,11 +36,36 @@ from domain.sap10_calculator.worksheet.heat_transmission import (
     heat_transmission_from_cert,
 )
 from domain.sap10_calculator.worksheet.heat_transmission import (
+    _part_geometry,  # pyright: ignore[reportPrivateUsage]
     _round_half_up,  # pyright: ignore[reportPrivateUsage]
     _window_bp_index,  # pyright: ignore[reportPrivateUsage]
 )
 
 
+def test_part_geometry_floorless_part_honours_full_key_contract() -> None:
+    # Arrange — a building part lodged with NO sap_floor_dimensions (e.g.
+    # a party-wall-only or RR-only extension; observed on 5 certs in a
+    # 2026 API sample). `_part_geometry`'s early return must expose the
+    # same dict keys as its full return: the §3.9 RR contribution block
+    # reads geom["rr_common_wall_area_m2"] / ["rr_gable_area_m2"] for
+    # EVERY part, so a missing key raises KeyError and blocks the cert.
+    floorless = make_building_part(floor_dimensions=[])
+    with_floors = make_building_part(
+        floor_dimensions=[make_floor_dimension(total_floor_area_m2=50.0)]
+    )
+
+    # Act
+    early = _part_geometry(floorless)
+    full = _part_geometry(with_floors)
+
+    # Assert — identical key contract; the RR/cantilever geometry is 0.0
+    # for a floorless part (no floor area ⇒ no RR shell or cantilever).
+    assert set(early.keys()) == set(full.keys())
+    assert early["rr_common_wall_area_m2"] == 0.0
+    assert early["rr_gable_area_m2"] == 0.0
+    assert early["cantilever_floor_area_m2"] == 0.0
+
+
 def test_roof_insulated_assumed_with_ni_thickness_uses_50mm_per_section_5_11_4() -> None:
     # Arrange — 346 corpus certs lodge roof_insulation_thickness="NI"
     # with descriptions like "Pitched, insulated (assumed)". The
@@ -168,21 +193,26 @@ def test_floor_insulated_assumed_with_ni_thickness_uses_50mm_per_table19_footnot
     assert result.floor_w_per_k == pytest.approx(31.0, abs=2.0)
 
 
-def test_solid_brick_as_built_insulated_assumed_uses_50mm_row_per_table6_footnote() -> None:
-    # Arrange — 128 corpus certs lodge solid-brick walls with
-    # wall_insulation_type=4 ("as-built / assumed") AND description
-    # "Solid brick, as built, insulated (assumed)". The description
-    # signals retrofit insulation that the assessor hasn't measured the
-    # thickness of; RdSAP 10 Table 6 footnote routes this to the 50 mm
-    # row. Without the description signal, type=4 alone would set
-    # wall_ins_present=False and the cascade would return the as-built
-    # U=1.7. With it, U = 0.55 at band B.
+def test_solid_brick_as_built_insulated_assumed_uses_as_built_row_per_table9_footnote() -> None:
+    # Arrange — an "as built, insulated (assumed)" description only renders
+    # on RECENT age bands (where as-built construction already includes
+    # insulation per Building Regs); an old band renders "no insulation
+    # (assumed)". RdSAP 10 Table 8/9 footnote routes to the 50 mm row only
+    # when insulation is "known to have been increased subsequently
+    # (otherwise 'as built' applies)" — an age-band assumption is NOT
+    # known retrofit, so the as-built row applies.
+    #
+    # Worksheet-validated: simulated case 9 (sandstone, band J, As Built
+    # → U 0.35) and case 10 (solid brick, band J, As Built → U 0.35) both
+    # return the as-built row, NOT the 50 mm bucket (which would give
+    # U=0.25). This was previously asserted at 55 W/K via an IMPOSSIBLE
+    # band-B + "insulated (assumed)" combination.
     # Geometry: 100 m² floor, 40 m perimeter, 2.5 m height, single
-    # storey → gross_wall = 100 m². walls_w_per_k expected = 0.55 × 100
-    # = 55 W/K.
+    # storey → gross_wall = 100 m². walls_w_per_k expected = 0.35 × 100
+    # = 35 W/K.
     main = make_building_part(
         identifier="Main Dwelling",
-        construction_age_band="B",
+        construction_age_band="J",
         wall_construction=3,
         wall_insulation_type=4,
         party_wall_construction=1,
@@ -211,7 +241,7 @@ def test_solid_brick_as_built_insulated_assumed_uses_50mm_row_per_table6_footnot
     result = heat_transmission_from_cert(epc)
 
     # Assert
-    assert result.walls_w_per_k == pytest.approx(55.0, abs=1.0)
+    assert result.walls_w_per_k == pytest.approx(35.0, abs=1.0)
 
 
 def test_solid_brick_as_built_no_insulation_assumed_stays_at_table6_as_built_row() -> None:
@@ -302,6 +332,58 @@ def test_cavity_as_built_insulated_assumed_uses_filled_cavity_row() -> None:
     assert result.walls_w_per_k == pytest.approx(70.0, abs=1.0)
 
 
+def test_cavity_as_built_partial_insulation_assumed_uses_as_built_row() -> None:
+    # Arrange — the EPC renders a cavity wall lodged wall_insulation_type=4
+    # (as-built / assumed) with description "Cavity wall, as built, partial
+    # insulation (assumed)" for age bands where the as-built construction
+    # carries only partial cavity fill. "Partial insulation" is the as-built
+    # thermal state of the age band, NOT a retrofit cavity fill — the spec
+    # routes it to the "Cavity as built" row, not "Filled cavity":
+    # RdSAP 10 Table 6 (England) "Cavity as built" band F = 1.0 vs
+    # "Filled cavity" band F = 0.40. A genuine fill renders the distinct
+    # "Cavity wall, filled cavity" description (wall_insulation_type=2),
+    # caught separately. Contrast the "insulated (assumed)" variant above,
+    # which the assessor judges as filled.
+    #
+    # Real-cert evidence: golden cert 0390-2954-3640 (detached, band F,
+    # cavity type 4, "partial insulation (assumed)") closes all four SAP
+    # metrics (PE/SAP/CO2/cost) on the as-built 1.0 row — at the filled
+    # 0.40 row its PE under-counts by ~28 kWh/m².
+    # Geometry: 100 m² floor, 40 m perimeter, 2.5 m height, single storey
+    # → gross_wall = 100 m². walls_w_per_k expected = 1.0 × 100 = 100 W/K.
+    main = make_building_part(
+        construction_age_band="F",
+        wall_construction=4,
+        wall_insulation_type=4,
+        party_wall_construction=1,
+        roof_construction=4,
+        floor_dimensions=[
+            make_floor_dimension(
+                total_floor_area_m2=100.0, room_height_m=2.5,
+                party_wall_length_m=0.0, heat_loss_perimeter_m=40.0, floor=0,
+            ),
+        ],
+    )
+    epc = make_minimal_sap10_epc(
+        total_floor_area_m2=100.0,
+        country_code="ENG",
+        sap_building_parts=[main],
+    )
+    epc.walls = [
+        EnergyElement(
+            description="Cavity wall, as built, partial insulation (assumed)",
+            energy_efficiency_rating=3,
+            environmental_efficiency_rating=3,
+        ),
+    ]
+
+    # Act
+    result = heat_transmission_from_cert(epc)
+
+    # Assert — U=1.0 × 100 m² gross wall = 100 W/K (as-built, not filled 70).
+    assert abs(result.walls_w_per_k - 100.0) <= 1.0
+
+
 def test_walls_description_measured_transmittance_overrides_construction_cascade() -> None:
     # Arrange — a full-SAP (not RdSAP) cert lodges the wall U-value
     # directly in walls[i].description ("Average thermal transmittance
@@ -1140,6 +1222,138 @@ def test_sap_building_part_has_basement_detects_main_wall_and_alt_wall_codes() -
     assert alt_is_basement.main_wall_is_basement is False  # main is still wc=4
 
 
+def test_explicit_wall_is_basement_flag_disambiguates_system_built_from_basement() -> None:
+    """RdSAP10 `wall_construction == 6` is canonically SYSTEM-BUILT
+    (`WALL_SYSTEM_BUILT`), but the gov-EPC basement heuristic hijacked it
+    (Elmhurst lodges both "SY System build" and "B Basement wall" as
+    code 6). The explicit `wall_is_basement` flag — set by the Elmhurst
+    mapper from the distinct "SY"/"B" codes — disambiguates:
+        - flag True  → basement (drives §5.17 u_basement_wall)
+        - flag False → system-built (drives the u_wall code-6 table)
+        - flag None  → fall back to the gov-EPC API code-6 heuristic
+    so the API path (which lodges basement as integer 6 with no flag) is
+    unchanged."""
+    from dataclasses import replace
+    # Arrange — three parts, all wall_construction=6, differing only in flag.
+    plain = make_building_part(
+        identifier=BuildingPartIdentifier.MAIN,
+        construction_age_band="G",
+        wall_construction=6, wall_insulation_type=4,
+        party_wall_construction=1, roof_construction=4,
+        floor_dimensions=[
+            make_floor_dimension(
+                total_floor_area_m2=80.0, room_height_m=2.5,
+                party_wall_length_m=0.0, heat_loss_perimeter_m=35.0, floor=0,
+            ),
+        ],
+    )
+    system_built = replace(plain, wall_is_basement=False)
+    basement = replace(plain, wall_is_basement=True)
+    api_code_6 = replace(plain, wall_is_basement=None)
+
+    # Act / Assert
+    assert system_built.main_wall_is_basement is False
+    assert basement.main_wall_is_basement is True
+    assert api_code_6.main_wall_is_basement is True  # API heuristic preserved
+
+    # Alt-wall mirror — same Optional disambiguation on SapAlternativeWall.
+    alt_system_built = SapAlternativeWall(
+        wall_area=14.24, wall_dry_lined="N", wall_construction=6,
+        wall_insulation_type=4, wall_thickness_measured="Y", is_basement=False,
+    )
+    alt_basement = SapAlternativeWall(
+        wall_area=14.24, wall_dry_lined="N", wall_construction=6,
+        wall_insulation_type=4, wall_thickness_measured="Y", is_basement=True,
+    )
+    alt_api_code_6 = SapAlternativeWall(
+        wall_area=14.24, wall_dry_lined="N", wall_construction=6,
+        wall_insulation_type=4, wall_thickness_measured="Y",
+    )
+    assert alt_system_built.is_basement_wall is False
+    assert alt_basement.is_basement_wall is True
+    assert alt_api_code_6.is_basement_wall is True
+
+
+def test_system_build_property_derives_from_main_wall_construction_type() -> None:
+    # Arrange — system-built is a WALL TYPE: RdSAP10 WALL_SYSTEM_BUILT=6
+    # on the MAIN wall. It shares the integer with basement, so a code-6
+    # main wall is system-built only when it is NOT flagged basement. The
+    # `system_build` property reads the wall type (wall_construction) + the
+    # dedicated basement flag — it does not need a separate dwelling-level
+    # field.
+    from dataclasses import replace
+    base_main = make_building_part(
+        identifier=BuildingPartIdentifier.MAIN,
+        construction_age_band="G",
+        wall_construction=6, wall_insulation_type=4,
+        party_wall_construction=1, roof_construction=4,
+        floor_dimensions=[
+            make_floor_dimension(
+                total_floor_area_m2=80.0, room_height_m=2.5,
+                party_wall_length_m=0.0, heat_loss_perimeter_m=35.0, floor=0,
+            ),
+        ],
+    )
+    system_built = make_minimal_sap10_epc(
+        sap_building_parts=[replace(base_main, wall_is_basement=False)],
+    )
+    basement = make_minimal_sap10_epc(
+        sap_building_parts=[replace(base_main, wall_is_basement=True)],
+    )
+    cavity = make_minimal_sap10_epc(
+        sap_building_parts=[replace(base_main, wall_construction=4)],
+    )
+    no_main = make_minimal_sap10_epc(sap_building_parts=[])
+
+    # Act / Assert — code 6 + not basement → system-built; code 6 + basement
+    # → not system-built; a non-6 wall type → not system-built; no main → None.
+    assert system_built.system_build is True
+    assert basement.system_build is False
+    assert cavity.system_build is False
+    assert no_main.system_build is None
+
+
+def test_system_built_addendum_clears_basement_on_code_6_walls_api_path() -> None:
+    # Arrange — gov-EPC API system-built cert: the per-wall code 6 can't be
+    # told from a basement at lodging time, so once the cert addendum marks
+    # the dwelling system-built, `from_api_response` clears the code-6
+    # basement heuristic. A genuine basement (no addendum signal) keeps it.
+    from dataclasses import replace
+
+    from datatypes.epc.domain.epc_property_data import Addendum
+    from datatypes.epc.domain.mapper import _clear_basement_flag_when_system_built  # pyright: ignore[reportPrivateUsage]
+
+    code_6_main = make_building_part(
+        identifier=BuildingPartIdentifier.MAIN,
+        construction_age_band="G",
+        wall_construction=6, wall_insulation_type=4,
+        party_wall_construction=1, roof_construction=4,
+        floor_dimensions=[
+            make_floor_dimension(
+                total_floor_area_m2=80.0, room_height_m=2.5,
+                party_wall_length_m=0.0, heat_loss_perimeter_m=35.0, floor=0,
+            ),
+        ],
+    )
+    system_built_cert = replace(
+        make_minimal_sap10_epc(sap_building_parts=[code_6_main]),
+        addendum=Addendum(system_build=True),
+    )
+    genuine_basement_cert = make_minimal_sap10_epc(sap_building_parts=[code_6_main])
+
+    # Act
+    cleared = _clear_basement_flag_when_system_built(system_built_cert)
+    untouched = _clear_basement_flag_when_system_built(genuine_basement_cert)
+
+    # Assert — system-built cert: code-6 main wall is no longer basement,
+    # and the wall-type-derived system_build reads True. Genuine basement
+    # (no addendum) is unchanged → still basement.
+    assert cleared.sap_building_parts[0].main_wall_is_basement is False
+    assert cleared.system_build is True
+    assert untouched.sap_building_parts[0].main_wall_is_basement is True
+    assert untouched.system_build is False
+
+
 def test_basement_alt_wall_uses_table_23_u_value_not_cascade() -> None:
     """RdSAP §5.17 / Table 23 governs basement-wall U-values: 0.7 for age
     A-F, 0.6 for G-H, 0.45 for I, 0.35 for J, ..., 0.26 for M. The

tests/domain/sap10_calculator/worksheet/test_section_cascade_pins.py

@@ -42,6 +42,7 @@ from tests.domain.sap10_calculator.worksheet import (
     _elmhurst_worksheet_000487 as _w000487,
     _elmhurst_worksheet_000490 as _w000490,
     _elmhurst_worksheet_000516 as _w000516,
+    _elmhurst_worksheet_001431_case6 as _w001431_case6,
 )
 
 
@@ -248,6 +249,152 @@ def test_section_3_line_refs_match_pdf(
     _pin(actual, expected, f"§3 {fixture_attr} {fixture_name}")
 
 
+def test_section_3_roof_windows_case6_match_pdf() -> None:
+    """§3 (27a) roof-window pin for simulated case 6 — the 6 room-in-roof
+    rooflights (window_wall_type=4 on the API side / "Roof of Room"
+    location on the site-notes side) must bill on (27a) at U_eff 2.1062,
+    not on (27) as vertical glazing. Validates the S0380.198/199 roof-
+    window routing against a real worksheet. Case 6 is pinned only on the
+    §3 window line refs (not added to `_FIXTURES`) because its dual main
+    heating system makes the §10/§12 per-system lines non-comparable —
+    see the fixture module docstring."""
+    # Arrange
+    epc = _w001431_case6.build_epc()
+
+    # Act
+    ht = heat_transmission_section_from_cert(epc)
+
+    # Assert
+    _pin(ht.windows_w_per_k, _w001431_case6.LINE_27_WINDOWS_W_PER_K, "§3 (27) case6")
+    _pin(
+        ht.roof_windows_w_per_k,
+        _w001431_case6.LINE_27A_ROOF_WINDOWS_W_PER_K,
+        "§3 (27a) case6",
+    )
+    _pin(
+        ht.total_external_element_area_m2,
+        _w001431_case6.LINE_31_TOTAL_EXTERNAL_AREA_M2,
+        "§3 (31) case6",
+    )
+    _pin(
+        ht.roof_w_per_k,
+        _w001431_case6.LINE_30_ROOF_W_PER_K,
+        "§3 (30) case6",
+    )
+
+
+def test_case6_main_2_emitter_and_control_extracted() -> None:
+    """Simulated case 6's §14.1 Main Heating2 lodges its OWN emitter
+    ("Underfloor Heating") and control ("SAP code 2110, ...") — the two
+    main systems heat different parts (Main 1 radiators/2106 living, Main
+    2 underfloor/2110 elsewhere). Pre-S0380.204 the extractor + mapper
+    dropped both (emitter='' / control=''), so the SAP 10.2 p.186 two-
+    systems-different-parts MIT could not read system 2's responsiveness
+    (underfloor → emitter 2 → R=0.75) or control type (2110 → type 3)."""
+    # Arrange / Act
+    epc = _w001431_case6.build_epc()
+    main_2 = epc.sap_heating.main_heating_details[1]
+
+    # Assert — emitter 2 (underfloor in screed → Table 4d R=0.75) +
+    # control 2110 (Table 4e type 3 zone control).
+    assert main_2.heat_emitter_type == 2
+    assert main_2.main_heating_control == 2110
+
+
+def test_section_4_hot_water_fuel_case6_match_pdf() -> None:
+    """(219) water-heating fuel for simulated case 6. The DHW boiler (Main
+    1, WHC 901) provides only 51% of space heating, so SAP 10.2 Appendix D
+    §D2.1(2) Equation D1 must weight η_winter by Main 1's (204) share, not
+    the dwelling total (202). Pre-S0380.206 the cascade fed Eq D1 the full
+    dwelling space load → over-weighted η_winter → HW −78 kWh."""
+    # Arrange / Act — real cascade (the §2.4 helper skips the cylinder gate).
+    ci = cert_to_inputs(_w001431_case6.build_epc())
+
+    # Assert
+    _pin(
+        ci.hot_water_kwh_per_yr,
+        _w001431_case6.LINE_219_HOT_WATER_FUEL_KWH,
+        "§4 (219) case6",
+    )
+
+
+def test_section_9a_per_system_fuel_case6_match_pdf() -> None:
+    """(211)/(213) per-system space-heating fuel for simulated case 6. The
+    dual oil boiler heats different parts (Main 1 radiators/2106 living,
+    Main 2 underfloor/2110 elsewhere), so SAP 10.2 p.186 applies the
+    two-systems-different-parts MIT: weighted responsiveness R = 0.51·1.0
+    + 0.49·0.75 = 0.8775 (Table 9b) and a rest-of-dwelling temperature
+    blended from each system's control schedule. That lands (98c) demand
+    11991.96 exact, so the per-system fuels pin. Pre-S0380.205 the cascade
+    used Main 1's control + R=1.0 for the whole dwelling → MIT +0.037 °C →
+    demand +61 kWh → both legs ~+1.3 % high."""
+    # Arrange / Act — pin the REAL cascade (the §2.4 section helper skips
+    # the interlock penalty + two-system MIT params, so use cert_to_inputs).
+    er = cert_to_inputs(_w001431_case6.build_epc()).energy_requirements
+
+    # Assert
+    _pin(
+        er.main_1_fuel_kwh_per_yr,
+        _w001431_case6.LINE_211_MAIN_1_FUEL_KWH,
+        "§9a (211) case6",
+    )
+    _pin(
+        er.main_2_fuel_kwh_per_yr,
+        _w001431_case6.LINE_213_MAIN_2_FUEL_KWH,
+        "§9a (213) case6",
+    )
+
+
+def test_section_4f_pumps_fans_case6_match_pdf() -> None:
+    """(231) pumps/fans pin for simulated case 6 — a DUAL-oil-boiler
+    detached dwelling. Worksheet (231) = 356 = (230c) central heating
+    pump 156 + (230d) oil boiler pump 200. (230c) is itself the two-
+    main-system circulation-pump pair per SAP 10.2 Table 4f note c
+    ("Where there are two main heating systems include two figures from
+    this table"): Main 1 41 kWh (pump age "2013 or later") + Main 2 115
+    kWh (pump age unknown). The pre-S0380.201 cascade summed only Main 1's
+    circulation pump (41) and gave (231) = 241."""
+    from domain.sap10_calculator.calculator import calculate_sap_from_inputs
+
+    # Arrange
+    epc = _w001431_case6.build_epc()
+
+    # Act
+    result = calculate_sap_from_inputs(cert_to_inputs(epc))
+
+    # Assert
+    _pin(
+        result.pumps_fans_kwh_per_yr,
+        _w001431_case6.LINE_231_PUMPS_FANS_KWH,
+        "§4f (231) case6",
+    )
+
+
+def test_section_5_pumps_fans_gains_case6_match_pdf() -> None:
+    """(70) pumps/fans internal-gain pin for simulated case 6. The dual oil
+    boiler serves different parts (51% radiators + 49% underfloor), so SAP
+    10.2 Table 5a note a) ("Where there are two main heating systems serving
+    different parts of the dwelling, assume each has its own circulation
+    pump and therefore include two figures from this table") bills TWO
+    central-heating-pump gains: Main 1 "2013 or later" (3 W) + Main 2
+    unknown date (7 W) = 10 W in the 8 heating months. The pre-S0380.202
+    cascade billed a single Main 1 pump (3 W)."""
+    # Arrange
+    epc = _w001431_case6.build_epc()
+
+    # Act
+    ig = internal_gains_section_from_cert(epc)
+
+    # Assert
+    assert ig is not None
+    for m in range(12):
+        _pin(
+            ig.pumps_fans_monthly_w[m],
+            _w001431_case6.LINE_70_PUMPS_FANS_GAINS_W[m],
+            f"§5 (70) case6 month {m + 1}",
+        )
+
+
 # ============================================================================
 # §4 Water heating — LINE_42..LINE_65 scalar + monthly tuples
 # ============================================================================

tests/repositories/epc/test_epc_round_trip.py

@@ -48,3 +48,37 @@ def test_epc_property_data_round_trips(schema_dir: str, db_engine: Engine) -> No
 
     # Assert
     assert reloaded == original
+
+
+def test_building_part_wall_insulation_thickness_preserves_int(
+    db_engine: Engine,
+) -> None:
+    # SAP 10.2 §5.7/Table 8: when the API lodges
+    # `wall_insulation_thickness == "measured"`, the mapper resolves the
+    # value to an int mm. The `epc_building_part.wall_insulation_thickness`
+    # column must therefore preserve int vs str on round-trip (JSONB), like
+    # its `roof_insulation_thickness` sibling — a plain str column would
+    # round-trip the int 100 back as "100" and corrupt the Table 8 lookup.
+    from dataclasses import replace
+
+    # Arrange — take a green fixture and force the measured-int case.
+    original = _load_epc("RdSAP-Schema-21.0.0")
+    assert original.sap_building_parts, "fixture must have a building part"
+    bp0 = replace(original.sap_building_parts[0], wall_insulation_thickness=100)
+    original = replace(
+        original,
+        sap_building_parts=[bp0, *original.sap_building_parts[1:]],
+    )
+
+    # Act
+    with Session(db_engine) as session:
+        epc_property_id = EpcPostgresRepository(session).save(original)
+        session.commit()
+    with Session(db_engine) as session:
+        reloaded = EpcPostgresRepository(session).get(epc_property_id)
+
+    # Assert — the int survives as an int, not the string "100".
+    assert reloaded is not None
+    value = reloaded.sap_building_parts[0].wall_insulation_thickness
+    assert value == 100
+    assert isinstance(value, int)