diff --git a/backend/documents_parser/elmhurst_extractor.py b/backend/documents_parser/elmhurst_extractor.py
index a8c9e596..196291b4 100644
--- a/backend/documents_parser/elmhurst_extractor.py
+++ b/backend/documents_parser/elmhurst_extractor.py
@@ -7,6 +7,7 @@ from datatypes.epc.surveys.elmhurst_site_notes import (
     BathsAndShowers,
     BuildingPartDimensions,
     CommunityHeating,
+    Conservatory,
     ElmhurstSiteNotes,
     ExtensionPart,
     FloorDetails,
@@ -30,6 +31,17 @@ from datatypes.epc.surveys.elmhurst_site_notes import (
 )
 
 
+def _parse_conservatory_storeys(raw: Optional[str]) -> float:
+    """Parse the §5 "Room Height" lodgement ("1 Storey", "1.5 Storey",
+    "1½ Storey") into the equivalent-storey count RdSAP 10 §6.1 translates
+    to a metre height. Defaults to 1.0 (single storey) when unparseable."""
+    if not raw:
+        return 1.0
+    text = raw.replace("½", ".5")
+    m = re.search(r"\d+(?:\.\d+)?", text)
+    return float(m.group(0)) if m else 1.0
+
+
 def _parse_solar_pitch_deg(raw: Optional[str]) -> Optional[int]:
     """Parse the §16.0 "Collector elevation" lodgement (e.g. "30°", "60°",
     or a bare integer). Returns None when absent or unparseable."""
@@ -81,6 +93,13 @@ class ElmhurstSiteNotesExtractor:
         except (ValueError, IndexError):
             return 0
 
+    def _float_val(self, label: str) -> Optional[float]:
+        v = self._next_val(label)
+        if not v:
+            return None
+        m = re.search(r"-?\d+(?:\.\d+)?", v)
+        return float(m.group(0)) if m else None
+
     def _date_val(self, label: str) -> date:
         v = self._next_val(label)
         if not v:
@@ -179,8 +198,39 @@ class ElmhurstSiteNotesExtractor:
         v = self._local_val(lines, label)
         return v is not None and v.lower() == "yes"
 
+    def _local_float(self, lines: List[str], label: str) -> Optional[float]:
+        v = self._local_val(lines, label)
+        if not v:
+            return None
+        m = re.search(r"-?\d+(?:\.\d+)?", v)
+        return float(m.group(0)) if m else None
+
     # --- section extractors ---
 
+    def _extract_conservatory(self) -> Optional[Conservatory]:
+        """Summary §5.0 — geometry of a conservatory (RdSAP 10 §6, PDF
+        p.49). Returns None when none is lodged. Scoped to the §5 block
+        so the generic labels ("Floor Area", "Room Height") can't collide
+        with §4 dimensions. A separated conservatory is still returned
+        (with `thermally_separated=True`); the mapper drops it per §6.2."""
+        if not self._bool_val("Is there a conservatory?"):
+            return None
+        lines = self._section_lines_first_end(
+            "5.0 Conservatory", ("7.0 Walls", "6.0 ", "Summary Information"),
+        )
+        return Conservatory(
+            thermally_separated=self._local_bool(
+                lines, "Is it thermally separated?"
+            ),
+            floor_area_m2=self._local_float(lines, "Floor Area [m2]") or 0.0,
+            double_glazed=self._local_bool(lines, "Double Glazed"),
+            glazed_perimeter_m=self._local_float(lines, "Glazed Perimeter [m]")
+            or 0.0,
+            room_height_storeys=_parse_conservatory_storeys(
+                self._local_val(lines, "Room Height")
+            ),
+        )
+
     def _extract_surveyor_info(self) -> SurveyorInfo:
         return SurveyorInfo(
             surveyor_code=self._str_val("Surveyor"),
@@ -1302,6 +1352,10 @@ class ElmhurstSiteNotesExtractor:
                 air_permeability_ap4_m3_h_m2 = float(ap4_raw.split()[0])
             except (ValueError, IndexError):
                 air_permeability_ap4_m3_h_m2 = None
+        # SAP 10.2 §2 (17) "Measured/design AP50" from a Blower Door test.
+        # Routes the cascade's (18) via `AP50 / 20 + (8)` (preferred over
+        # AP4). Absent when the test method is "Not available".
+        ap50_raw = self._local_float(pressure_lines, "Pressure Test Result (AP50)")
         # Summary §12.1 "Mechanical Ventilation Type" — scoped to §12.1
         # body so the global "Type" labels in §14 / §15 can't shadow it.
         mv_lines = self._section_lines(
@@ -1350,6 +1404,7 @@ class ElmhurstSiteNotesExtractor:
             mechanical_ventilation=self._bool_val("Mechanical Ventilation"),
             pressure_test_method=self._str_val("Test Method"),
             air_permeability_ap4_m3_h_m2=air_permeability_ap4_m3_h_m2,
+            air_permeability_ap50_m3_h_m2=ap50_raw,
             mechanical_ventilation_type=mechanical_ventilation_type,
             mechanical_ventilation_pcdf_reference=mev_pcdf_reference,
             wet_rooms_count=wet_rooms_count,
@@ -1820,6 +1875,7 @@ class ElmhurstSiteNotesExtractor:
             construction_age_band=self._extract_main_age_band(),
             dimensions=self._extract_dimensions(),
             has_conservatory=self._bool_val("Is there a conservatory?"),
+            conservatory=self._extract_conservatory(),
             walls=self._extract_walls(),
             roof=self._extract_roof(),
             floor=self._extract_floor(),
diff --git a/backend/documents_parser/tests/fixtures/Summary_001431_case44.pdf b/backend/documents_parser/tests/fixtures/Summary_001431_case44.pdf
new file mode 100644
index 00000000..4312e6c1
Binary files /dev/null and b/backend/documents_parser/tests/fixtures/Summary_001431_case44.pdf differ
diff --git a/datatypes/epc/domain/epc_property_data.py b/datatypes/epc/domain/epc_property_data.py
index baf1db00..f69ede90 100644
--- a/datatypes/epc/domain/epc_property_data.py
+++ b/datatypes/epc/domain/epc_property_data.py
@@ -202,6 +202,10 @@ class SapVentilation:
     # Pulse pressure test, m³/h per m² of envelope area. When present the
     # cascade routes (18) via the AP4 formula `0.263 × AP4^0.924 + (8)`.
     air_permeability_ap4_m3_h_m2: Optional[float] = None
+    # SAP 10.2 §2 (17) — air permeability at 50 Pa from a Blower Door test,
+    # m³/h per m² of envelope area. When present the cascade routes (18)
+    # via `AP50 / 20 + (8)` (preferred over AP4).
+    air_permeability_ap50_m3_h_m2: Optional[float] = None
     # SAP 10.2 §2 (23a)/(24a..d) — Elmhurst "Mechanical Ventilation Type"
     # string mapped to the `MechanicalVentilationKind` enum name (e.g.
     # "EXTRACT_OR_PIV_OUTSIDE" for MEV decentralised). The cascade uses
@@ -261,6 +265,33 @@ class SapRoofWindow:
     window_location: Union[int, str] = 0
 
 
+@dataclass(frozen=True)
+class SapConservatory:
+    """RdSAP 10 §6.1 (PDF p.49) — a NON-SEPARATED (heated) conservatory.
+
+    Its floor area and volume are added to the dwelling total (TFA (4),
+    volume (5)); its fully-glazed walls bill as a window (27) and its
+    fully-glazed roof as a rooflight (27a); the floor adds a ground-loss
+    term (28a). U-values come from RdSAP 10 Table 25 (p.51): double 6 mm
+    window 3.1 / roof 3.4 / g 0.76; single window 4.8 / roof 5.3 / g 0.85.
+
+    `room_height_storeys` is the equivalent number of storey heights of
+    the dwelling to the nearest half (Summary §5 "Room Height", gov-API
+    glazed building part), translated to a metre height per §6.1:
+    1 storey → ground-floor room height; 1½ → ground + 0.25 + 0.5×first;
+    2 → ground + 0.25 + first; etc.
+
+    A SEPARATED conservatory (§6.2) is disregarded entirely and is never
+    represented here (`thermally_separated` stays a guard for the cascade).
+    """
+
+    floor_area_m2: float
+    glazed_perimeter_m: float
+    double_glazed: bool
+    thermally_separated: bool
+    room_height_storeys: float
+
+
 @dataclass
 class SapWindow:
     frame_material: Optional[str]
@@ -774,6 +805,10 @@ class EpcPropertyData:
     # has no roof windows; for cert-cascade fixtures the bootstrap path
     # lodges per-window area + raw U.
     sap_roof_windows: Optional[List[SapRoofWindow]] = None
+    # RdSAP 10 §6.1 — geometry of a non-separated (heated) conservatory.
+    # None when no conservatory is lodged or it is thermally separated
+    # (§6.2 disregards separated conservatories).
+    sap_conservatory: Optional[SapConservatory] = None
     calculation_software_version: Optional[str] = None  # Do we care about this?
     mechanical_vent_duct_placement: Optional[int] = None
     mechanical_vent_duct_insulation: Optional[int] = None
diff --git a/datatypes/epc/domain/mapper.py b/datatypes/epc/domain/mapper.py
index 159c0f92..448abaff 100644
--- a/datatypes/epc/domain/mapper.py
+++ b/datatypes/epc/domain/mapper.py
@@ -25,6 +25,7 @@ from datatypes.epc.domain.epc_property_data import (
     SapEnergySource,
     SapFlatDetails,
     SapFloorDimension,
+    SapConservatory,
     SapHeating,
     SapRoofWindow,
     SapRoomInRoof,
@@ -69,6 +70,7 @@ from datatypes.epc.surveys.elmhurst_site_notes import (
     AlternativeWall as ElmhurstAlternativeWall,
     BuildingPartDimensions as ElmhurstBuildingPartDimensions,
     CommunityHeating,
+    Conservatory as ElmhurstConservatory,
     ElmhurstSiteNotes,
     FloorDetails as ElmhurstFloorDetails,
     MainHeating as ElmhurstMainHeating,
@@ -415,12 +417,25 @@ class EpcPropertyDataMapper:
                     ext.room_in_roof.floor_area_m2
                     for ext in survey.extensions
                     if ext.room_in_roof is not None
+                )
+                # RdSAP 10 §6.1 (PDF p.49) — a non-separated conservatory's
+                # floor area is added to the dwelling total floor area. TFA
+                # drives occupancy → §5 internal gains + §4 hot-water demand,
+                # so it must include the conservatory (the worksheet's (4) =
+                # 95.38 carries it). Separated conservatories (§6.2) are
+                # disregarded.
+                + (
+                    survey.conservatory.floor_area_m2
+                    if survey.conservatory is not None
+                    and not survey.conservatory.thermally_separated
+                    else 0.0
                 ),
                 2,
             ),
             built_form=built_form,
             property_type=property_type,
             has_conservatory=survey.has_conservatory,
+            sap_conservatory=_map_elmhurst_conservatory(survey.conservatory),
             blocked_chimneys_count=survey.ventilation.blocked_chimneys_count,
             number_of_storeys=survey.number_of_storeys,
             hydro=survey.renewables.hydro_electricity_generated_kwh > 0,
@@ -2077,8 +2092,14 @@ class EpcPropertyDataMapper:
                         else None
                     ),
                 )
+                # RdSAP 10 §6.1 — exclude the glazed conservatory BP from the
+                # fabric loop; it is carried as `sap_conservatory` below and
+                # billed by the §6.1 cascade (window/rooflight/floor), not as
+                # a dwelling building part.
                 for bp in schema.sap_building_parts
+                if getattr(bp, "glazed_perimeter", None) is None
             ],
+            sap_conservatory=_api_sap_conservatory(schema.sap_building_parts),
             renewable_heat_incentive=RenewableHeatIncentive(
                 space_heating_kwh=float(
                     schema.renewable_heat_incentive.space_heating_existing_dwelling
@@ -2483,6 +2504,33 @@ def _measurement_value(field: Any) -> float:
     return float(field)
 
 
+def _api_sap_conservatory(building_parts: Any) -> Optional[SapConservatory]:
+    """Build the domain `SapConservatory` from the gov-API glazed
+    conservatory building part — the part the API uses for a NON-SEPARATED
+    conservatory (RdSAP 10 §6.1, PDF p.49), identified by a lodged
+    `glazed_perimeter` (real dwelling parts carry fabric + floor dimensions
+    instead, never `glazed_perimeter`). Only type-4 (non-separated)
+    conservatories lodge this BP; separated ones (§6.2) lodge nothing, so
+    its presence is the §6.1 signal. Mirror of `_map_elmhurst_conservatory`
+    for the API path — proven equivalent by cross-mapper parity (the cascade
+    reads `epc.sap_conservatory` identically). Returns None when absent."""
+    if not building_parts:
+        return None
+    for bp in building_parts:
+        if getattr(bp, "glazed_perimeter", None) is None:
+            continue
+        return SapConservatory(
+            floor_area_m2=_measurement_value(bp.floor_area),
+            glazed_perimeter_m=_measurement_value(bp.glazed_perimeter),
+            double_glazed=bp.double_glazed == "Y",
+            # The gov API only lodges this glazed BP for NON-separated
+            # (type-4) conservatories; separated ones (§6.2) lodge no BP.
+            thermally_separated=False,
+            room_height_storeys=float(_measurement_value(bp.room_height)),
+        )
+    return None
+
+
 def _total_floor_area_from_building_parts(building_parts: Any) -> Optional[float]:
     """Sum per-bp `sap_floor_dimensions[*].total_floor_area` (plus each bp's
     `sap_room_in_roof.floor_area` when present) to recover the precise
@@ -2507,6 +2555,13 @@ def _total_floor_area_from_building_parts(building_parts: Any) -> Optional[float
     total = 0.0
     found = False
     for bp in building_parts:
+        # RdSAP 10 §6.1 — a non-separated conservatory's glazed BP (no floor
+        # dimensions) adds its floor area to the dwelling TFA. TFA drives
+        # occupancy → §4/§5 demand, so the conservatory must be in the sum.
+        if getattr(bp, "glazed_perimeter", None) is not None:
+            total += _measurement_value(bp.floor_area)
+            found = True
+            continue
         floor_dims: Any = bp.sap_floor_dimensions or []
         for fd in floor_dims:
             total += _measurement_value(fd.total_floor_area)
@@ -4003,12 +4058,88 @@ def _api_build_room_in_roof(
         # §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)
+    type_2 = getattr(bp_rir, "room_in_roof_type_2", None)
+    if type_2 is not None:
+        rir.detailed_surfaces = _api_type_2_surfaces(type_2)
     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)
     return rir
 
 
+def _api_type_2_surfaces(
+    type_2: Any,
+) -> Optional[List[SapRoomInRoofSurface]]:
+    """Translate the §3.9.2 Simplified Type 2 block into the per-surface
+    list the cascade's Detailed-RR branch consumes — MIRRORING the
+    worksheet-validated Summary path (`_map_elmhurst_rir_surface`,
+    is_simplified, validated to 1e-4 by cohort cert 000565). Unlike the
+    Type 1 block (gable lengths only, billed raw L × 2.45), Type 2 lodges
+    gable + common-wall lengths AND heights, so the spec's §3.9.2 areas
+    apply:
+      common wall  → `L × (0.25 + H)`                      (billed at uw)
+      gable        → `L × (0.25 + H_gable)
+                      − Σ_each_common (H_gable − H_common,n)² / 2`
+    The gable correction is taken over ALL common walls for an exposed/
+    party/sheltered gable (the worksheet evaluates it literally, incl. the
+    H_gable=0 absent-gable case → a negative area that deducts from the
+    A_RR residual without billing a physical wall); a Connected gable
+    (Table 4 row 4, U=0) sums only the common walls it overtops, matching
+    the Summary's connected-gable branch. The `gable_wall_type_*` code
+    routes the kind (0 Party / 1 Exposed / 2 Sheltered / 3 Connected) via
+    `_api_type_1_gable_kind`; U-values are left to the cascade (no per-
+    gable U is lodged on the API path)."""
+    cw_heights = [
+        float(h)
+        for length, h in (
+            (type_2.common_wall_length_1, type_2.common_wall_height_1),
+            (type_2.common_wall_length_2, type_2.common_wall_height_2),
+        )
+        if length is not None and h is not None and length > 0 and h > 0
+    ]
+    surfaces: List[SapRoomInRoofSurface] = []
+    gable_specs = (
+        (type_2.gable_wall_type_1, type_2.gable_wall_length_1,
+         type_2.gable_wall_height_1),
+        (type_2.gable_wall_type_2, type_2.gable_wall_length_2,
+         type_2.gable_wall_height_2),
+    )
+    for gable_type, length, height in gable_specs:
+        # Length is mandatory; H may be 0 for the §3.9.2 absent-gable
+        # quadratic (only when common walls drive the correction).
+        if length is None or length <= 0 or height is None:
+            continue
+        if height <= 0 and not cw_heights:
+            continue
+        kind = _api_type_1_gable_kind(gable_type)
+        length_m, height_m = float(length), float(height)
+        if cw_heights:
+            if kind == "connected_wall":
+                correction = sum(
+                    ((height_m - h) ** 2) / 2.0 for h in cw_heights if height_m > h
+                )
+            else:
+                correction = sum(((height_m - h) ** 2) / 2.0 for h in cw_heights)
+            area = _round_half_up_2dp(1.0, length_m * (0.25 + height_m) - correction)
+        else:
+            area = _round_half_up_2dp(length_m, height_m)
+        surfaces.append(SapRoomInRoofSurface(kind=kind, area_m2=area))
+    common_specs = (
+        (type_2.common_wall_length_1, type_2.common_wall_height_1),
+        (type_2.common_wall_length_2, type_2.common_wall_height_2),
+    )
+    for length, height in common_specs:
+        if length is None or height is None or length <= 0 or height <= 0:
+            continue
+        surfaces.append(
+            SapRoomInRoofSurface(
+                kind="common_wall",
+                area_m2=_round_half_up_2dp(float(length), 0.25 + float(height)),
+            )
+        )
+    return surfaces or None
+
+
 def _api_rir_detailed_surfaces(
     details: Any,
     *,
@@ -5222,6 +5353,24 @@ def _elmhurst_roof_window_u_value(w: ElmhurstWindow) -> float:
     return w.u_value + _ELMHURST_ROOF_WINDOW_INCLINATION_ADJUSTMENT_W_PER_M2K
 
 
+def _map_elmhurst_conservatory(
+    cons: Optional[ElmhurstConservatory],
+) -> Optional[SapConservatory]:
+    """RdSAP 10 §6 — translate the Summary §5 conservatory geometry into
+    the domain `SapConservatory`. A SEPARATED conservatory (§6.2, PDF
+    p.49) is disregarded entirely, so it maps to None (the cascade adds
+    nothing). Returns None when no conservatory is lodged."""
+    if cons is None or cons.thermally_separated:
+        return None
+    return SapConservatory(
+        floor_area_m2=cons.floor_area_m2,
+        glazed_perimeter_m=cons.glazed_perimeter_m,
+        double_glazed=cons.double_glazed,
+        thermally_separated=cons.thermally_separated,
+        room_height_storeys=cons.room_height_storeys,
+    )
+
+
 def _map_elmhurst_roof_window(w: ElmhurstWindow) -> SapRoofWindow:
     return SapRoofWindow(
         area_m2=w.area_m2,
@@ -6893,5 +7042,6 @@ def _map_elmhurst_ventilation(
             else (False if has_suspended_timber_floor else None)
         ),
         air_permeability_ap4_m3_h_m2=v.air_permeability_ap4_m3_h_m2,
+        air_permeability_ap50_m3_h_m2=v.air_permeability_ap50_m3_h_m2,
         mechanical_ventilation_kind=_elmhurst_mv_kind(v.mechanical_ventilation_type),
     )
diff --git a/datatypes/epc/domain/tests/test_from_rdsap_schema.py b/datatypes/epc/domain/tests/test_from_rdsap_schema.py
index 054e9864..77be7628 100644
--- a/datatypes/epc/domain/tests/test_from_rdsap_schema.py
+++ b/datatypes/epc/domain/tests/test_from_rdsap_schema.py
@@ -2228,3 +2228,132 @@ class TestRoomInRoofDetailedSlopeAndStudWall:
         assert studs[0].insulation_thickness_mm == 75
         assert abs(commons[0].area_m2 - 10.32) <= 1e-9
         assert commons[0].insulation_thickness_mm is None
+
+
+class TestRoomInRoofType2SimplifiedQuadratic:
+    """RdSAP 10 §3.9.2 Simplified Type 2 RR — the gov API lodges gable +
+    common-wall lengths AND heights under `room_in_roof_type_2`. The block
+    was undeclared → dropped → the cascade billed the whole A_RR shell at
+    the Table-18-col-4 default (over-count → under-rate, 7 corpus certs at
+    signed −5.02). The mapper now MIRRORS the worksheet-validated Summary
+    §3.9.2 areas (cross-mapper parity, proven identical on cohort cert
+    000565): common walls L×(0.25+H), gables L×(0.25+H) − Σ(H−H_cw)²/2."""
+
+    def test_from_api_response_applies_3_9_2_gable_quadratic(self) -> None:
+        # Arrange — two common walls (L=8, H=1 → cw_heights [1,1]); an
+        # exposed gable (L=10, H=2) and a party gable (L=6, H=2).
+        #   common wall  = round(8 × (0.25+1))            = 10.00
+        #   exposed gable= round(10 × (0.25+2) − 2×(2−1)²/2) = round(22.5−1) = 21.50
+        #   party gable  = round(6 × (0.25+2) − 1.0)      = round(13.5−1)  = 12.50
+        cert = load("21_0_1.json")
+        rir = cert["sap_building_parts"][0]["sap_room_in_roof"]
+        rir.pop("room_in_roof_type_1", None)
+        rir["room_in_roof_type_2"] = {
+            "gable_wall_type_1": 1, "gable_wall_length_1": 10.0,
+            "gable_wall_height_1": 2.0,
+            "gable_wall_type_2": 0, "gable_wall_length_2": 6.0,
+            "gable_wall_height_2": 2.0,
+            "common_wall_length_1": 8.0, "common_wall_height_1": 1.0,
+            "common_wall_length_2": 8.0, "common_wall_height_2": 1.0,
+        }
+
+        # Act
+        result = EpcPropertyDataMapper.from_api_response(cert)
+
+        # Assert
+        rir_part = result.sap_building_parts[0].sap_room_in_roof
+        assert rir_part is not None
+        surfaces = rir_part.detailed_surfaces
+        assert surfaces is not None
+        ext = [s for s in surfaces if s.kind == "gable_wall_external"]
+        party = [s for s in surfaces if s.kind == "gable_wall"]
+        commons = [s for s in surfaces if s.kind == "common_wall"]
+        assert len(ext) == 1 and abs(ext[0].area_m2 - 21.50) <= 1e-9
+        assert len(party) == 1 and abs(party[0].area_m2 - 12.50) <= 1e-9
+        assert len(commons) == 2
+        assert abs(commons[0].area_m2 - 10.00) <= 1e-9
+
+
+class TestNonSeparatedConservatoryApiMirror:
+    """RdSAP 10 §6.1 (PDF p.49) — the gov API lodges a NON-SEPARATED
+    conservatory (conservatory_type=4) as a glazed "building part" carrying
+    only {floor_area, room_height, double_glazed, glazed_perimeter}. The
+    block was undeclared → `from_dict` dropped it → the conservatory was
+    silently lost (5 corpus certs over-rating). The mapper now splits it
+    into `EpcPropertyData.sap_conservatory`, excludes it from the fabric
+    building-part loop, and adds its floor area to TFA.
+
+    Validation is cross-mapper parity, NOT a corpus back-solve: the API
+    mapper feeds the SAME worksheet-validated §6.1 cascade
+    (`conservatory_geometry`, pinned to 1e-4 against the case-44 Summary)
+    as the Elmhurst path — so the API conservatory fabric is correct by
+    construction."""
+
+    def test_from_api_response_splits_out_conservatory_building_part(
+        self,
+    ) -> None:
+        # Arrange — a 1-BP dwelling (ground-floor room height 2.45 m) plus a
+        # non-separated double-glazed conservatory glazed BP.
+        from datatypes.epc.domain.epc_property_data import SapConservatory
+        from domain.sap10_calculator.worksheet.conservatory import (
+            conservatory_geometry,
+        )
+
+        baseline_tfa = EpcPropertyDataMapper.from_api_response(
+            load("21_0_1.json")
+        ).total_floor_area_m2
+
+        cert = load("21_0_1.json")
+        cert["conservatory_type"] = 4
+        cert["sap_building_parts"].append(
+            {
+                "floor_area": 12.0,
+                "room_height": 1,
+                "double_glazed": "Y",
+                "glazed_perimeter": 9.0,
+            }
+        )
+
+        # Act
+        epc = EpcPropertyDataMapper.from_api_response(cert)
+
+        # Assert — conservatory split out; the glazed BP is NOT a fabric part.
+        assert epc.sap_conservatory == SapConservatory(
+            floor_area_m2=12.0,
+            glazed_perimeter_m=9.0,
+            double_glazed=True,
+            thermally_separated=False,
+            room_height_storeys=1.0,
+        )
+        assert len(epc.sap_building_parts) == 1
+        # §6.1: the conservatory floor area joins TFA (drives occupancy).
+        assert abs(epc.total_floor_area_m2 - (baseline_tfa + 12.0)) <= 1e-9
+
+        # Cross-mapper parity: the shared §6.1 cascade derives the same
+        # surfaces it does for the case-44 Summary — glazed wall = exposed
+        # perimeter × ground-floor room height (9.0 × 2.45 = 22.05); glazed
+        # roof = floor / cos(20°) (12.0 / 0.9397 = 12.77); Table 25 double
+        # U_eff = 1/(1/3.1 + 0.04) = 2.758 (wall) / 1/(1/3.4 + 0.04) = 2.993.
+        geom = conservatory_geometry(epc)
+        assert geom is not None
+        assert abs(geom.glazed_wall_area_m2 - 22.05) <= 1e-4
+        assert abs(geom.glazed_roof_area_m2 - 12.77) <= 1e-4
+        assert abs(geom.wall_u_eff - 2.7580) <= 1e-4
+        assert abs(geom.roof_u_eff - 2.9930) <= 1e-4
+
+    def test_separated_conservatory_lodges_no_glazed_building_part(self) -> None:
+        # Arrange — a separated conservatory (type 2/3) lodges NO glazed BP
+        # (verified across the gov corpus); the dwelling is unchanged.
+        from domain.sap10_calculator.worksheet.conservatory import (
+            conservatory_geometry,
+        )
+
+        cert = load("21_0_1.json")
+        cert["conservatory_type"] = 2
+
+        # Act
+        epc = EpcPropertyDataMapper.from_api_response(cert)
+
+        # Assert — §6.2: disregarded; no conservatory geometry.
+        assert epc.sap_conservatory is None
+        assert conservatory_geometry(epc) is None
diff --git a/datatypes/epc/schema/rdsap_schema_21_0_0.py b/datatypes/epc/schema/rdsap_schema_21_0_0.py
index 4f7e7e40..c9565d9b 100644
--- a/datatypes/epc/schema/rdsap_schema_21_0_0.py
+++ b/datatypes/epc/schema/rdsap_schema_21_0_0.py
@@ -236,12 +236,29 @@ class RoomInRoofDetails:
     common_wall_height_2: Optional[float] = None
 
 
+@dataclass
+class RoomInRoofType2:
+    """RdSAP §3.9.2 Simplified Type 2 RR — gable + common-wall geometry.
+    See `rdsap_schema_21_0_1.RoomInRoofType2`. Previously dropped."""
+    gable_wall_type_1: Optional[int] = None
+    gable_wall_type_2: Optional[int] = None
+    gable_wall_length_1: Optional[float] = None
+    gable_wall_length_2: Optional[float] = None
+    gable_wall_height_1: Optional[float] = None
+    gable_wall_height_2: Optional[float] = None
+    common_wall_length_1: Optional[float] = None
+    common_wall_length_2: Optional[float] = None
+    common_wall_height_1: Optional[float] = None
+    common_wall_height_2: Optional[float] = None
+
+
 @dataclass
 class SapRoomInRoof:
     """Room-in-roof details. insulation and roof_room_connected removed in schema 21.0.0."""
     floor_area: Union[int, float]
     construction_age_band: str
     room_in_roof_type_1: Optional[RoomInRoofType1] = None
+    room_in_roof_type_2: Optional[RoomInRoofType2] = None
     room_in_roof_details: Optional[RoomInRoofDetails] = None
 
 
diff --git a/datatypes/epc/schema/rdsap_schema_21_0_1.py b/datatypes/epc/schema/rdsap_schema_21_0_1.py
index 37714034..45f1ee46 100644
--- a/datatypes/epc/schema/rdsap_schema_21_0_1.py
+++ b/datatypes/epc/schema/rdsap_schema_21_0_1.py
@@ -278,14 +278,38 @@ class RoomInRoofDetails:
     common_wall_height_2: Optional[float] = None
 
 
+@dataclass
+class RoomInRoofType2:
+    """RdSAP §3.9.2 Simplified Type 2 RR — a room-in-roof bounded by
+    continuous common walls (accessible common-wall height < 1.8 m, so the
+    space counts as RR not a separate storey). Lodges gable + common-wall
+    lengths AND heights (unlike Type 1, gable lengths only). `gable_wall_
+    type_*` is the Table 4 variant (0 Party / 1 Exposed / 2 Sheltered /
+    3 Connected). Previously undeclared → dropped by `from_dict`, so the
+    cascade billed the whole A_RR shell at the Table-18-col-4 default
+    (over-count → under-rate)."""
+    gable_wall_type_1: Optional[int] = None
+    gable_wall_type_2: Optional[int] = None
+    gable_wall_length_1: Optional[float] = None
+    gable_wall_length_2: Optional[float] = None
+    gable_wall_height_1: Optional[float] = None
+    gable_wall_height_2: Optional[float] = None
+    common_wall_length_1: Optional[float] = None
+    common_wall_length_2: Optional[float] = None
+    common_wall_height_1: Optional[float] = None
+    common_wall_height_2: Optional[float] = None
+
+
 @dataclass
 class SapRoomInRoof:
     floor_area: Union[int, float]
     construction_age_band: str
-    # Two real-API shapes coexist: older certs (cohort 6035, 0240, test
-    # fixture 21_0_1.json) lodge the Simplified Type 1 wrapper; newer
-    # certs (9501) lodge the Detailed-RR block. Accept both.
+    # Three real-API shapes coexist: older certs (cohort 6035, 0240, test
+    # fixture 21_0_1.json) lodge the Simplified Type 1 wrapper; some lodge
+    # the §3.9.2 Simplified Type 2 wrapper (gable + common-wall geometry);
+    # newer certs (9501) lodge the Detailed-RR block. Accept all three.
     room_in_roof_type_1: Optional[RoomInRoofType1] = None
+    room_in_roof_type_2: Optional[RoomInRoofType2] = None
     room_in_roof_details: Optional[RoomInRoofDetails] = None
 
 
@@ -358,6 +382,16 @@ class SapBuildingPart:
     # redacts the backing insulation. Previously undeclared → dropped.
     wall_u_value: Optional[float] = None
     floor_u_value: Optional[float] = None
+    # RdSAP 10 §6.1 (PDF p.49) — a NON-SEPARATED conservatory is lodged by
+    # the gov API as a glazed "building part" carrying ONLY these four
+    # fields (no fabric, no floor dimensions); `conservatory_type == 4` at
+    # the property level. Previously undeclared → dropped by `from_dict`,
+    # so the conservatory was silently lost on the API path. The mapper
+    # splits this BP out into `EpcPropertyData.sap_conservatory`.
+    floor_area: Optional[Union[Measurement, int, float]] = None
+    room_height: Optional[Union[Measurement, int, float]] = None
+    double_glazed: Optional[str] = None
+    glazed_perimeter: Optional[Union[Measurement, int, float]] = None
 
 
 @dataclass
diff --git a/datatypes/epc/surveys/elmhurst_site_notes.py b/datatypes/epc/surveys/elmhurst_site_notes.py
index 4614d33c..3b179253 100644
--- a/datatypes/epc/surveys/elmhurst_site_notes.py
+++ b/datatypes/epc/surveys/elmhurst_site_notes.py
@@ -202,6 +202,9 @@ class VentilationAndCooling:
     # SAP 10.2 §2 (17a) AP4 reading from §12.2 "Pressure Test Result
     # (AP4)" — only present when `pressure_test_method == "Pulse"`.
     air_permeability_ap4_m3_h_m2: Optional[float] = None
+    # SAP 10.2 §2 (17) AP50 reading from §12.2 "Pressure Test Result
+    # (AP50)" — present for a Blower Door test. Routes (18) via AP50/20.
+    air_permeability_ap50_m3_h_m2: Optional[float] = None
     # Summary §12.1 "Mechanical Ventilation Type" — e.g. "Mechanical
     # extract, decentralised (MEV dc)". None when `mechanical_ventilation
     # is False` (no MV system).
@@ -478,6 +481,21 @@ class ExtensionPart:
     room_in_roof: Optional[RoomInRoof] = None
 
 
+@dataclass
+class Conservatory:
+    """Summary §5 geometry of a NON-SEPARATED conservatory (RdSAP 10
+    §6.1). `room_height_storeys` is the lodged equivalent-storey count
+    ("1 Storey" → 1.0, "1.5 Storey" → 1.5); the mapper/cascade translate
+    it to a metre height. A SEPARATED conservatory (§6.2) is disregarded,
+    so `thermally_separated=True` records are dropped before the cascade."""
+
+    thermally_separated: bool
+    floor_area_m2: float
+    double_glazed: bool
+    glazed_perimeter_m: float
+    room_height_storeys: float
+
+
 @dataclass
 class ElmhurstSiteNotes:
     surveyor_info: SurveyorInfo
@@ -560,3 +578,9 @@ class ElmhurstSiteNotes:
     # cold loft instead of a room-in-roof). The mapper translates the
     # surface table into a `SapRoomInRoof` attached to the Main bp.
     room_in_roof: Optional[RoomInRoof] = None
+
+    # §5.0 Conservatory geometry — None when the dwelling has no
+    # conservatory (`has_conservatory=False`). Populated (incl. for
+    # separated conservatories) so the mapper can apply the §6.1/§6.2
+    # rule; the mapper drops separated ones.
+    conservatory: Optional[Conservatory] = None
diff --git a/domain/sap10_calculator/rdsap/cert_to_inputs.py b/domain/sap10_calculator/rdsap/cert_to_inputs.py
index f4a86295..c8a59fcf 100644
--- a/domain/sap10_calculator/rdsap/cert_to_inputs.py
+++ b/domain/sap10_calculator/rdsap/cert_to_inputs.py
@@ -4986,6 +4986,9 @@ def ventilation_from_cert(
     # cascade's `(18) = 0.263 × AP4^0.924 + (8)` formula; absent value
     # falls through to the components-based (16) ach.
     ap4 = sv.air_permeability_ap4_m3_h_m2 if sv is not None else None
+    # SAP 10.2 §2 (17) — AP50 Blower Door reading routes (18) via
+    # `AP50 / 20 + (8)`, preferred over AP4 when both are lodged.
+    ap50 = sv.air_permeability_ap50_m3_h_m2 if sv is not None else None
     # SAP 10.2 §2 (23a)/(24a..d) — MV kind dispatch chooses the (25)m
     # effective-ach formula. The Elmhurst mapper translates the lodged
     # "Mechanical Ventilation Type" string to an enum *name*; resolve
@@ -5023,6 +5026,7 @@ def ventilation_from_cert(
         window_pct_draught_proofed=float(epc.percent_draughtproofed or 0),
         sheltered_sides=int(sv.sheltered_sides) if sv is not None and sv.sheltered_sides is not None else 2,
         air_permeability_ap4=ap4,
+        air_permeability_ap50=ap50,
         mv_kind=mv_kind,
         mv_system_ach=mv_system_ach,
         **wind_kwargs,
diff --git a/domain/sap10_calculator/worksheet/conservatory.py b/domain/sap10_calculator/worksheet/conservatory.py
new file mode 100644
index 00000000..b9729e1f
--- /dev/null
+++ b/domain/sap10_calculator/worksheet/conservatory.py
@@ -0,0 +1,149 @@
+"""RdSAP 10 §6.1 — non-separated (heated) conservatory geometry.
+
+A non-separated conservatory is treated as part of the dwelling
+(RdSAP 10 Specification, 9th June 2025, §6.1 + Table 25, pages 49-51):
+
+  - its floor area and volume are added to TFA (4) and volume (5);
+  - its fully-glazed walls bill as a window — line (27) — at the Table 25
+    "U-value of window"; its glazed roof bills as a rooflight — line (27a)
+    — at the Table 25 "U-value of roof window"; both U-values already
+    include the §3.2 curtain resistance (R=0.04 m²K/W);
+  - its floor adds a ground-loss term — line (28a) — via BS EN ISO 13370,
+    taken as an uninsulated solid floor with 300 mm walls (§5.12 note,
+    spec p.43), exposed perimeter = glazed perimeter;
+  - its glazed wall + glazed roof + floor areas count toward the total
+    exposed area (31) and hence thermal bridging (36); the fully-glazed
+    "structure" walls/roof themselves add nothing (the glazing IS the
+    window/rooflight).
+
+Its roof area is the floor area / cos(20°) and its wall area is the
+exposed perimeter × height; the height is translated from the lodged
+equivalent storey count (§6.1): 1 storey → ground-floor room height;
+1½ → ground + 0.25 + 0.5×first; 2 → ground + 0.25 + first; etc.
+
+A SEPARATED conservatory (§6.2) is disregarded entirely — the mapper
+maps it to None, so it never reaches this module.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from decimal import Decimal, ROUND_HALF_UP
+from math import cos, radians
+from typing import Final, Optional
+
+from datatypes.epc.domain.epc_property_data import EpcPropertyData
+
+# RdSAP 10 §6.1 — conservatory roof area = floor area / cos(20°); §6.1
+# also fixes the rooflight solar pitch at 20°.
+CONSERVATORY_ROOF_PITCH_DEG: Final[float] = 20.0
+_COS_ROOF_PITCH: Final[float] = cos(radians(CONSERVATORY_ROOF_PITCH_DEG))
+
+# RdSAP 10 Table 25 (PDF p.51) — default conservatory glazing U-values
+# (W/m²K, INCLUSIVE of the §3.2 curtain resistance) and g-values. The
+# Summary lodges only double vs single (no triple), so a bool selects the
+# row: True → double (6 mm gap), False → single.
+_TABLE_25_WALL_U: Final[dict[bool, float]] = {True: 3.1, False: 4.8}
+_TABLE_25_ROOF_U: Final[dict[bool, float]] = {True: 3.4, False: 5.3}
+_TABLE_25_G_VALUE: Final[dict[bool, float]] = {True: 0.76, False: 0.85}
+_TABLE_25_FRAME_FACTOR: Final[float] = 0.70  # Table 25 — wood/PVC frame
+
+# SAP 10.2 §3.2 formula (2) curtain/blind resistance. Table 25 U-values
+# are "adjusted for curtains" already, so the EFFECTIVE conduction U is
+# 1 / (1/U_table25 + 0.04) — the same transform `heat_transmission`
+# applies to regular windows/rooflights.
+_CURTAIN_RESISTANCE_M2K_PER_W: Final[float] = 0.04
+
+# RdSAP 10 §5.12 (spec p.43) — a non-separated conservatory floor is an
+# uninsulated solid ground floor with 300 mm walls.
+_CONSERVATORY_WALL_THICKNESS_MM: Final[int] = 300
+_AREA_ROUND_DP: Final[int] = 2
+
+
+def _round2(value: float) -> float:
+    """RdSAP 10 §15 (p.66): element areas + conservatory height → 2 d.p."""
+    return float(
+        Decimal(str(value)).quantize(Decimal("0.01"), rounding=ROUND_HALF_UP)
+    )
+
+
+@dataclass(frozen=True)
+class ConservatoryGeometry:
+    """Derived §6.1 geometry for one non-separated conservatory. Areas and
+    height are rounded to 2 d.p. per RdSAP 10 §15."""
+
+    height_m: float
+    floor_area_m2: float
+    glazed_wall_area_m2: float
+    glazed_roof_area_m2: float
+    glazed_perimeter_m: float
+    wall_u_raw: float          # Table 25 window U, pre-curtain
+    roof_u_raw: float          # Table 25 roof-window U, pre-curtain
+    wall_u_eff: float          # post-curtain conduction U for line (27)
+    roof_u_eff: float          # post-curtain conduction U for line (27a)
+    g_value: float
+    frame_factor: float
+    volume_m3: float
+
+
+def _conservatory_height_m(epc: EpcPropertyData, storeys: float) -> float:
+    """Translate the equivalent storey count into a metre height per
+    RdSAP 10 §6.1 using the dwelling's per-storey room heights:
+
+      1 storey  → ground-floor room height
+      1½ storey → ground + 0.25 + 0.5 × first-floor room height
+      2 storey  → ground + 0.25 + first-floor room height
+      etc.
+
+    Room heights are taken from the Main building part's floor
+    dimensions (floor 0 = ground, 1 = first, ...). Returns 0.0 when no
+    storeys are lodged (defensive; the conservatory then bills no walls)."""
+    parts = epc.sap_building_parts or []
+    heights: list[float] = []
+    if parts:
+        fds = sorted(
+            parts[0].sap_floor_dimensions,
+            key=lambda fd: fd.floor if fd.floor is not None else 0,
+        )
+        heights = [fd.room_height_m for fd in fds if fd.room_height_m]
+    if not heights:
+        return 0.0
+    n_full = int(storeys)
+    height = heights[0]
+    for s in range(1, n_full):
+        height += 0.25 + heights[min(s, len(heights) - 1)]
+    if storeys - n_full >= 0.5:
+        height += 0.25 + 0.5 * heights[min(n_full, len(heights) - 1)]
+    return _round2(height)
+
+
+def conservatory_geometry(
+    epc: EpcPropertyData,
+) -> Optional[ConservatoryGeometry]:
+    """Build the §6.1 conservatory geometry, or None when there is no
+    (non-separated) conservatory."""
+    cons = epc.sap_conservatory
+    if cons is None or cons.thermally_separated:
+        return None
+    height = _conservatory_height_m(epc, cons.room_height_storeys)
+    floor_area = cons.floor_area_m2
+    glazed_perimeter = cons.glazed_perimeter_m
+    glazed_wall = _round2(glazed_perimeter * height)
+    glazed_roof = _round2(floor_area / _COS_ROOF_PITCH)
+    dg = cons.double_glazed
+    wall_u_raw = _TABLE_25_WALL_U[dg]
+    roof_u_raw = _TABLE_25_ROOF_U[dg]
+    return ConservatoryGeometry(
+        height_m=height,
+        floor_area_m2=floor_area,
+        glazed_wall_area_m2=glazed_wall,
+        glazed_roof_area_m2=glazed_roof,
+        glazed_perimeter_m=glazed_perimeter,
+        wall_u_raw=wall_u_raw,
+        roof_u_raw=roof_u_raw,
+        wall_u_eff=1.0 / (1.0 / wall_u_raw + _CURTAIN_RESISTANCE_M2K_PER_W),
+        roof_u_eff=1.0 / (1.0 / roof_u_raw + _CURTAIN_RESISTANCE_M2K_PER_W),
+        g_value=_TABLE_25_G_VALUE[dg],
+        frame_factor=_TABLE_25_FRAME_FACTOR,
+        volume_m3=floor_area * height,
+    )
diff --git a/domain/sap10_calculator/worksheet/dimensions.py b/domain/sap10_calculator/worksheet/dimensions.py
index f48e24d5..792770b4 100644
--- a/domain/sap10_calculator/worksheet/dimensions.py
+++ b/domain/sap10_calculator/worksheet/dimensions.py
@@ -21,6 +21,7 @@ from dataclasses import dataclass
 from typing import Final
 
 from datatypes.epc.domain.epc_property_data import EpcPropertyData, SapBuildingPart
+from domain.sap10_calculator.worksheet.conservatory import conservatory_geometry
 
 _DEFAULT_STOREY_HEIGHT_M: Final[float] = 2.5
 
@@ -145,17 +146,28 @@ def dimensions_from_cert(epc: EpcPropertyData) -> Dimensions:
     total_storey_count = max(part_storey_counts) if part_storey_counts else 0
 
     has_storeys = sum_per_storey_area_m2 > 0
+    # `avg_height` (used by §2 (9) dwelling height → infiltration) is a
+    # property of the dwelling's storeys, so the conservatory is excluded
+    # from it. The conservatory IS added to TFA (4) and volume (5) per
+    # RdSAP 10 §6.1 ("The floor area and volume of a non-separated
+    # conservatory are added to the total floor area and volume of the
+    # dwelling") — it just doesn't form a storey.
     avg_height = (
         sum_per_storey_volume_m3 / sum_per_storey_area_m2
         if has_storeys
         else _DEFAULT_STOREY_HEIGHT_M
     )
+    cons = conservatory_geometry(epc)
+    cons_floor_area_m2 = cons.floor_area_m2 if cons is not None else 0.0
+    cons_volume_m3 = cons.volume_m3 if cons is not None else 0.0
     return Dimensions(
         total_floor_area_m2=(
-            sum_per_storey_area_m2 if has_storeys else epc.total_floor_area_m2
+            sum_per_storey_area_m2 + cons_floor_area_m2
+            if has_storeys
+            else epc.total_floor_area_m2
         ),
         volume_m3=(
-            sum_per_storey_volume_m3
+            sum_per_storey_volume_m3 + cons_volume_m3
             if has_storeys
             else epc.total_floor_area_m2 * _DEFAULT_STOREY_HEIGHT_M
         ),
diff --git a/domain/sap10_calculator/worksheet/heat_transmission.py b/domain/sap10_calculator/worksheet/heat_transmission.py
index 83668e6f..d12b7da9 100644
--- a/domain/sap10_calculator/worksheet/heat_transmission.py
+++ b/domain/sap10_calculator/worksheet/heat_transmission.py
@@ -71,6 +71,7 @@ from domain.sap10_ml.rdsap_uvalues import (
     u_wall,
     u_window,
 )
+from domain.sap10_calculator.worksheet.conservatory import conservatory_geometry
 from math import cos, floor, radians, sqrt
 
 
@@ -123,6 +124,9 @@ _DEFAULT_DOOR_AREA_M2: Final[float] = 1.85
 # deducts from that wall, not the main wall.
 _CORRIDOR_DOOR_U_W_PER_M2K: Final[float] = 1.4
 _DEFAULT_STOREY_HEIGHT_M: Final[float] = 2.5
+# RdSAP 10 §5.12 (spec p.43) — a non-separated conservatory floor is an
+# uninsulated solid ground floor with 300 mm walls.
+_CONSERVATORY_WALL_THICKNESS_MM: Final[int] = 300
 # SAP10.2 §3.2 curtain/blind thermal resistance applied to windows (and
 # roof windows) — turns raw window U into the worksheet's (27) effective U.
 _WINDOW_CURTAIN_RESISTANCE_M2K_PER_W: Final[float] = 0.04
@@ -396,6 +400,32 @@ def _joined_main_roof_descriptions(roofs: list[Any]) -> Optional[str]:
     return " | ".join(parts)
 
 
+def _main_roof_descriptions_by_kind(
+    roofs: list[Any],
+) -> tuple[Optional[str], Optional[str]]:
+    """Partition the non-RR roof descriptions into ``(pitched, flat)`` joins.
+
+    The deduplicated ``epc.roofs[]`` list cannot be indexed 1:1 against the
+    building parts (190/329 multi-part certs have len(roofs) != len(parts)),
+    so each part's ``u_roof`` historically consumed the SINGLE join of every
+    roof description. That leaks one part's insulation state onto another: a
+    "Flat, no insulation" extension dragged a "Pitched, insulated (assumed)"
+    main roof to the uninsulated 2.30, ~3x over-stating its heat loss (cert
+    100010129331: roof 110.5 -> ~28 W/K, +13 SAP). Splitting by flat vs
+    pitched/sloping lets each part match its own kind; the global join
+    (`_joined_main_roof_descriptions`) stays the fallback when a part's kind
+    has no matching entry. "Roof room(s)" entries are dropped (they carry
+    their own §3.9/§3.10 shell cascade)."""
+    pitched: list[str] = []
+    flat: list[str] = []
+    for e in roofs:
+        d = getattr(e, "description", "")
+        if not d or "roof room" in d.lower():
+            continue
+        (flat if "flat" in d.lower() else pitched).append(d)
+    return (" | ".join(pitched) or None, " | ".join(flat) or None)
+
+
 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
@@ -613,6 +643,9 @@ def heat_transmission_from_cert(
 
     country = Country.from_code(epc.country_code)
     roof_description = _joined_main_roof_descriptions(epc.roofs)
+    pitched_roof_description, flat_roof_description = (
+        _main_roof_descriptions_by_kind(epc.roofs)
+    )
     wall_description = _joined_descriptions(epc.walls)
     floor_description = _joined_descriptions(epc.floors)
 
@@ -884,8 +917,19 @@ def heat_transmission_from_cert(
         roof_thickness_explicitly_zero = (
             isinstance(raw_roof_thickness, int) and raw_roof_thickness == 0
         )
+        # RdSAP 10 §5.11 — match THIS part's roof to its own kind's lodged
+        # description (flat vs pitched/sloping) rather than the global join,
+        # so a flat "no insulation" part does not drag a pitched insulated
+        # part to the uninsulated 2.30. Fall back to the global join when the
+        # part's kind has no matching `epc.roofs[]` entry.
+        part_roof_is_flat = "flat" in (part.roof_construction_type or "").lower()
+        matched_roof_description = (
+            flat_roof_description if part_roof_is_flat else pitched_roof_description
+        )
+        if matched_roof_description is None:
+            matched_roof_description = roof_description
         effective_roof_description = (
-            None if roof_thickness_explicitly_zero else roof_description
+            None if roof_thickness_explicitly_zero else matched_roof_description
         )
         # RdSAP 10 §5.11 Table 18 page 45: column (3) "Flat roof" applies
         # when the per-bp roof construction lodges as a flat roof and the
@@ -1368,6 +1412,51 @@ def heat_transmission_from_cert(
     # door line.
     doors += _CORRIDOR_DOOR_U_W_PER_M2K * corridor_door_area
     roof_windows_w_per_k = roof_windows_w_per_k_total
+
+    # RdSAP 10 §6.1 (PDF p.49) + Table 25 (p.51) — a non-separated
+    # conservatory. Its fully-glazed walls bill as a window (27), its
+    # glazed roof as a rooflight (27a), and its floor adds a ground-loss
+    # term (28a) via BS EN ISO 13370 (uninsulated solid floor, 300 mm
+    # walls per §5.12; exposed perimeter = glazed perimeter). The glazed
+    # wall + roof + floor areas join (31)/(36) external area; the fully-
+    # glazed "structure" walls/roof add nothing (the glazing IS the
+    # window/rooflight). A separated conservatory (§6.2) is mapped to
+    # None upstream and never reaches here.
+    cons_geom = conservatory_geometry(epc)
+    cons_windows_w_per_k: float = 0.0
+    if cons_geom is not None:
+        cons_windows_w_per_k = (
+            cons_geom.glazed_wall_area_m2 * cons_geom.wall_u_eff
+        )
+        roof_windows_w_per_k += (
+            cons_geom.glazed_roof_area_m2 * cons_geom.roof_u_eff
+        )
+        u_cons_floor = u_floor(
+            country=country,
+            age_band=primary_age,
+            construction=None,
+            insulation_thickness_mm=0,
+            area_m2=cons_geom.floor_area_m2,
+            perimeter_m=cons_geom.glazed_perimeter_m,
+            wall_thickness_mm=_CONSERVATORY_WALL_THICKNESS_MM,
+            # Force the solid-floor branch of BS EN ISO 13370 regardless of
+            # age band (§5.12: conservatory floor is an uninsulated SOLID
+            # ground floor — the A/B suspended-timber default must not fire).
+            description="Solid",
+        )
+        floor += u_cons_floor * cons_geom.floor_area_m2
+        cons_external_area = (
+            cons_geom.glazed_wall_area_m2
+            + cons_geom.glazed_roof_area_m2
+            + cons_geom.floor_area_m2
+        )
+        total_external_area += cons_external_area
+        bridging += dwelling_y * cons_external_area
+    # Fold the conservatory glazed wall into the (27) window readout. The
+    # `windows` accumulator is partially-typed upstream (the per-window
+    # `u_value` arrives as `Any`); `float(...)` re-asserts the strict float
+    # type as we add the strictly-typed conservatory term.
+    windows = float(windows) + cons_windows_w_per_k
     fabric_heat_loss = (
         walls + roof + floor + party + windows + roof_windows_w_per_k + doors  # (33)
     )
diff --git a/domain/sap10_calculator/worksheet/solar_gains.py b/domain/sap10_calculator/worksheet/solar_gains.py
index 8d3d12a4..04de4982 100644
--- a/domain/sap10_calculator/worksheet/solar_gains.py
+++ b/domain/sap10_calculator/worksheet/solar_gains.py
@@ -36,6 +36,10 @@ from math import cos, radians, sin
 from typing import Final
 
 from datatypes.epc.domain.epc_property_data import EpcPropertyData, SapWindow
+from domain.sap10_calculator.worksheet.conservatory import (
+    CONSERVATORY_ROOF_PITCH_DEG,
+    conservatory_geometry,
+)
 from domain.sap10_calculator.tables.pcdb.postcode_weather import PostcodeClimate
 from domain.sap10_calculator.climate.appendix_u import (
     horizontal_solar_irradiance_w_per_m2,
@@ -435,6 +439,48 @@ def solar_gains_from_cert(
         o: _sum_tuples(*per_orientation[o]) for o in Orientation
     }
 
+    # RdSAP 10 §6.1 (PDF p.49) + Table 25 note (p.51): "The orientation of
+    # windows in a conservatory is not recorded, thus solar gains are
+    # calculated using the default solar flux (East/West orientation, with
+    # 20° pitch for roof windows)." Average overshading per §7 (Table 6d).
+    # The glazed wall bills onto the (76) East line (vertical, Z=z_vertical);
+    # the glazed roof onto the (82) roof-window line (20° pitch, Z=1.0).
+    cons = conservatory_geometry(epc)
+    if cons is not None:
+        cons_wall_monthly = tuple(
+            window_solar_gain_w(
+                area_m2=cons.glazed_wall_area_m2,
+                surface_flux_w_per_m2=surface_solar_flux_w_per_m2(
+                    orientation=Orientation.E, pitch_deg=90.0,
+                    region=region, month=m,
+                ),
+                g_perpendicular=cons.g_value,
+                frame_factor=cons.frame_factor,
+                overshading_factor=z_vertical,
+            )
+            for m in _MONTHS
+        )
+        cons_roof_monthly = tuple(
+            window_solar_gain_w(
+                area_m2=cons.glazed_roof_area_m2,
+                surface_flux_w_per_m2=surface_solar_flux_w_per_m2(
+                    orientation=Orientation.E,
+                    pitch_deg=CONSERVATORY_ROOF_PITCH_DEG,
+                    region=region, month=m,
+                ),
+                g_perpendicular=cons.g_value,
+                frame_factor=cons.frame_factor,
+                overshading_factor=_HORIZONTAL_Z,
+            )
+            for m in _MONTHS
+        )
+        per_orientation_summed[Orientation.E] = _sum_tuples(
+            per_orientation_summed[Orientation.E], cons_wall_monthly,
+        )
+        roof_windows_monthly = _sum_tuples(
+            roof_windows_monthly, cons_roof_monthly,
+        )
+
     total = _sum_tuples(
         *per_orientation_summed.values(),
         roof_windows_monthly,
diff --git a/domain/sap10_ml/rdsap_uvalues.py b/domain/sap10_ml/rdsap_uvalues.py
index b2e76b8f..33b9741c 100644
--- a/domain/sap10_ml/rdsap_uvalues.py
+++ b/domain/sap10_ml/rdsap_uvalues.py
@@ -589,6 +589,35 @@ def u_wall(
     ):
         u0 = _u_stone_thin_wall_age_a_to_e(construction, wall_thickness_mm)
         if u0 is not None:
+            # RdSAP 10 §5.8 + Table 14 (PDF p.41-42) — added External/Internal
+            # insulation on a stone wall: U = 1/(1/U₀ + R_ins), with U₀ the
+            # RAW §5.6 stone result (the Table-6 footnote (a) 1.7 cap does NOT
+            # apply to the insulated path — same rule the brick branch below
+            # and the dry-lined granite pin 000565 follow). λ defaults to
+            # 0.04 W/m·K per §5.8 final note. Mirrors the WALL_SOLID_BRICK
+            # insulated branch; without it a stone wall lodging code 1/3 +
+            # a thickness was billed at its UNINSULATED U (e.g. sandstone
+            # 520 mm + 100 mm internal: 1.64 → 0.30), the dominant cause of
+            # the wall_insulation_type=3 corpus under-rate cluster.
+            if (
+                wall_insulation_type in (
+                    _WALL_INSULATION_EXTERNAL, _WALL_INSULATION_INTERNAL,
+                )
+                and insulation_thickness_mm is not None
+                and insulation_thickness_mm > 0
+            ):
+                r_ins = _r_insulation_table_14(
+                    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(
+                    Decimal(str(u_unrounded)).quantize(
+                        Decimal("0.01"), rounding=ROUND_HALF_UP
+                    )
+                )
             if dry_lined:
                 # Round to 2 d.p. — worksheet (29a) A×U product uses
                 # the 2-d.p.-displayed U (cf. 000565 Main alt_wall_1:
diff --git a/domain/sap10_ml/tests/test_rdsap_uvalues.py b/domain/sap10_ml/tests/test_rdsap_uvalues.py
index 8d4e3612..38efc93c 100644
--- a/domain/sap10_ml/tests/test_rdsap_uvalues.py
+++ b/domain/sap10_ml/tests/test_rdsap_uvalues.py
@@ -725,6 +725,80 @@ def test_u_wall_stone_sandstone_thin_wall_age_a_120mm_uses_5_6_sandstone_formula
     assert abs(result - 3.7408) <= 1e-3
 
 
+def test_u_wall_stone_sandstone_with_internal_insulation_applies_5_8_table_14_r_value() -> None:
+    # Arrange — RdSAP 10 §5.8 + Table 14 (PDF p.41-42): a stone wall lodging
+    # External/Internal insulation (wall_insulation_type 1/3) + a thickness
+    # gets the same R-value adjustment as solid brick, applied to the RAW §5.6
+    # U₀. Mirrors corpus cert 100052159386 (Sandstone, 520 mm, 100 mm internal):
+    #   U₀ = 54.876 × 520^(-0.561) = 1.6433
+    #   R  = 0.025 × 100 + 0.25    = 2.75   (Table 14, λ = 0.04)
+    #   U  = 1 / (1/1.6433 + 2.75) = 0.2977 → 0.30 (2 d.p.)
+    # Before this branch the wall was billed at its UNINSULATED U (≈1.64),
+    # the dominant cause of the wall_insulation_type=3 corpus under-rate cluster.
+
+    # Act
+    result = u_wall(
+        country=Country.ENG,
+        age_band="A",
+        construction=WALL_STONE_SANDSTONE,
+        insulation_thickness_mm=100,
+        insulation_present=True,
+        wall_insulation_type=3,
+        dry_lined=False,
+        wall_thickness_mm=520,
+    )
+
+    # Assert
+    assert abs(result - 0.30) <= 1e-4
+
+
+def test_u_wall_stone_sandstone_insulated_feeds_raw_u0_not_table_6_cap() -> None:
+    # Arrange — the Table-6 footnote (a) 1.7 cap applies ONLY to the as-built
+    # row; the insulated §5.8 path takes the RAW §5.6 U₀ (same rule the brick
+    # branch and the dry-lined granite pin 000565 follow). At W=120 mm the raw
+    # sandstone U₀ = 3.7408 (> 1.7), so the 100 mm internal result must be
+    #   1 / (1/3.7408 + 2.75) = 0.331 → 0.33   (raw),
+    # NOT the capped 1 / (1/1.7 + 2.75) = 0.30. The 0.33 vs 0.30 split proves
+    # the cap is bypassed on the insulated path.
+
+    # Act
+    result = u_wall(
+        country=Country.ENG,
+        age_band="A",
+        construction=WALL_STONE_SANDSTONE,
+        insulation_thickness_mm=100,
+        insulation_present=True,
+        wall_insulation_type=3,
+        dry_lined=False,
+        wall_thickness_mm=120,
+    )
+
+    # Assert
+    assert abs(result - 0.33) <= 1e-4
+
+
+def test_u_wall_stone_granite_with_external_insulation_applies_5_8_table_14_r_value() -> None:
+    # Arrange — granite/whinstone §5.6 formula + §5.8 external insulation:
+    #   U₀ = 45.315 × 120^(-0.513) = 3.8871
+    #   R  = 0.025 × 50 + 0.25     = 1.50   (Table 14, λ = 0.04)
+    #   U  = 1 / (1/3.8871 + 1.50) = 0.567 → 0.57 (2 d.p.)
+
+    # Act
+    result = u_wall(
+        country=Country.ENG,
+        age_band="A",
+        construction=WALL_STONE_GRANITE,
+        insulation_thickness_mm=50,
+        insulation_present=True,
+        wall_insulation_type=1,
+        dry_lined=False,
+        wall_thickness_mm=120,
+    )
+
+    # Assert
+    assert abs(result - 0.57) <= 1e-4
+
+
 def test_u_wall_stone_granite_age_g_with_wall_thickness_ignores_5_6_formula_per_age_a_to_e_gate() -> None:
     # Arrange — §5.6 (PDF p.40) heading explicitly scopes the formula
     # to "age bands A to E". For age F onwards Table 6 gives literal
diff --git a/tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_001431_case44.py b/tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_001431_case44.py
new file mode 100644
index 00000000..49318a42
--- /dev/null
+++ b/tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_001431_case44.py
@@ -0,0 +1,144 @@
+"""Mapper-driven cascade pin against the Elmhurst P960-0001-001431
+"simulated case 44" worksheet — a 2-storey mid-terrace with a NON-SEPARATED
+(heated, type-4) DOUBLE-glazed CONSERVATORY.
+
+Case 44 is the 1e-4 oracle for RdSAP 10 §6.1 (PDF p.49) + Table 25 (p.51).
+The Summary §5 lodges: Floor Area 12.00 m², Glazed Perimeter 9.00 m,
+Double Glazed Yes, thermally separated No, Room Height 1 Storey. From that
+the §6.1 cascade derives (all verified against the P960 §3 to 1e-4):
+
+  - conservatory height = ground-floor room height = 2.60 m (1 storey);
+  - glazed WALL → window (27): A = perimeter × height = 9.0 × 2.60 = 23.40,
+    U = 1/(1/3.1 + 0.04) = 2.758 (Table 25 double 3.1 + §3.2 curtain);
+  - glazed ROOF → rooflight (27a): A = floor_area / cos(20°) = 12.77,
+    U = 1/(1/3.4 + 0.04) = 2.993 (Table 25 roof 3.4 + curtain);
+  - FLOOR → ground floor (28a): A = 12.00, U = 0.89 via BS EN ISO 13370
+    (uninsulated solid, 300 mm walls, P = glazed perimeter 9.0);
+  - the fully-glazed structure walls/roof bill at U=0 (the glazing IS the
+    window/rooflight) — they contribute nothing but DO count their glazed
+    area toward (31)/(36);
+  - TFA (4) += 12.00 → 95.38; volume (5) += 12.00 × 2.60 = 31.20 → 257.16.
+
+Like the other `_elmhurst_worksheet_001431_case*` fixtures this does NOT
+hand-build the EpcPropertyData: it routes the Summary PDF through
+ElmhurstSiteNotesExtractor + from_elmhurst_site_notes so the pin exercises
+the WHOLE extractor + mapper + calculator pipeline.
+
+Source: user-simulated PDFs at `sap worksheets/golden fixture debugging/
+simulated case 44/`. The Summary is mirrored into the tracked
+`backend/documents_parser/tests/fixtures/Summary_001431_case44.pdf` so the
+test runs without depending on the unstaged workspace.
+
+Worksheet pin targets (P960-0001-001431, "11a. SAP rating" UK-average
+rating block our cascade reproduces):
+- (4)   TFA, m²                                = 95.3800
+- (5)   Dwelling volume, m³                     = 257.1630
+- (27)  Windows (31.5795 main + 64.5374 cons)   = 96.1169
+- (27a) Roof windows (conservatory glazed roof) = 38.2201
+- (28a) Ground floor (10.7364 main + 10.6800)   = 21.4164
+- (29a) External walls                          = 35.5852
+- (30)  External roof                           = 7.4688
+- (31)  Total net area of external elements     = 294.2900
+- (33)  Fabric heat loss, W/K                    = 207.3274
+- (36)  Thermal bridges (0.080 × (31))           = 23.5432
+
+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_case44.pdf"
+)
+
+LINE_4_TFA_M2: Final[float] = 95.3800
+LINE_5_VOLUME_M3: Final[float] = 257.1630
+LINE_27_WINDOWS_W_PER_K: Final[float] = 96.1169
+LINE_27A_ROOF_WINDOWS_W_PER_K: Final[float] = 38.2201
+LINE_28A_FLOOR_W_PER_K: Final[float] = 21.4164
+LINE_29A_WALLS_W_PER_K: Final[float] = 35.5852
+LINE_30_ROOF_W_PER_K: Final[float] = 7.4688
+LINE_31_EXTERNAL_AREA_M2: Final[float] = 294.2900
+LINE_33_FABRIC_W_PER_K: Final[float] = 207.3274
+LINE_36_THERMAL_BRIDGING_W_PER_K: Final[float] = 23.5432
+
+# Demand-side line refs (Jan column, UK-average rating block). These
+# integrate the WHOLE §6.1 conservatory chain end-to-end:
+#  - (73) internal gains — the conservatory floor area enters TFA (4),
+#    which drives occupancy → §5 appliance/cooking/metabolic gains;
+#  - (83) solar gains — the glazed wall (E/W flux, 90° pitch) + glazed
+#    roof (E/W flux, 20° pitch) at Table 25 g=0.76, FF=0.70;
+#  - (95) useful gains = (84) total gains × the §7 utilisation factor —
+#    matches only when fabric (33), ventilation (38) AND gains (84) all
+#    agree, so it is the single tightest end-to-end conservatory pin;
+#  - (99) space heating per m² = (98c)/(4) — the integrated demand.
+LINE_73_INTERNAL_GAINS_JAN_W: Final[float] = 625.1759
+LINE_83_SOLAR_GAINS_JAN_W: Final[float] = 495.8655
+LINE_95_USEFUL_GAINS_JAN_W: Final[float] = 1079.6510
+LINE_99_SPACE_HEATING_PER_M2_KWH: Final[float] = 89.8073
+
+# NB — the full SAP value (72.9517) + (272) CO2 (3241.8656) are NOT pinned
+# here. The case-44 Summary PDF omits the House-Coal secondary heater
+# (SAP 633, 60% eff) that the P960 worksheet's descriptor block carries
+# (the same secondary as case 43); routed through the extractor the
+# Summary therefore yields NO secondary system, and the residual SAP/CO2
+# gap is exactly that missing secondary (main+secondary CO2 1927.31 +
+# 563.92 = 2491.23 vs cascade 2141.46 → +349.77 ≈ the 350 kg deficit).
+# This is a Summary-input defect, independent of §6.1 — every
+# conservatory-affected line ref above reproduces the P960 EXACTLY.
+
+
+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/value token sequences).
+    Mirror of the helper in the other `_elmhurst_worksheet_*` fixtures.
+    """
+    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-44 Summary through extractor + mapper.
+    No hand-built EpcPropertyData — the extractor and mapper are part of
+    the test target. This module is a pin PROVIDER (build_epc + LINE_*
+    constants); the collected assertions live in
+    `test_section_cascade_pins`."""
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_PDF)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+    return EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)
diff --git a/tests/domain/sap10_calculator/worksheet/test_heat_transmission.py b/tests/domain/sap10_calculator/worksheet/test_heat_transmission.py
index d1ed0c92..d841746e 100644
--- a/tests/domain/sap10_calculator/worksheet/test_heat_transmission.py
+++ b/tests/domain/sap10_calculator/worksheet/test_heat_transmission.py
@@ -38,6 +38,7 @@ from domain.sap10_calculator.worksheet.heat_transmission import (
 from domain.sap10_calculator.worksheet.heat_transmission import (
     _alt_wall_w_per_k,  # pyright: ignore[reportPrivateUsage]
     _joined_main_roof_descriptions,  # pyright: ignore[reportPrivateUsage]
+    _main_roof_descriptions_by_kind,  # pyright: ignore[reportPrivateUsage]
     _part_geometry,  # pyright: ignore[reportPrivateUsage]
     _round_half_up,  # pyright: ignore[reportPrivateUsage]
     _window_bp_index,  # pyright: ignore[reportPrivateUsage]
@@ -82,6 +83,80 @@ def test_joined_main_roof_descriptions_keeps_pure_rr_fallback() -> None:
     assert result == "Roof room(s), no insulation (assumed)"
 
 
+def test_main_roof_descriptions_by_kind_splits_flat_from_pitched() -> None:
+    # Arrange — a cert with a pitched insulated main roof + a flat
+    # uninsulated extension. The deduplicated epc.roofs[] cannot be indexed
+    # 1:1 against the parts, so each part must match its own KIND's
+    # description: the flat part's "no insulation" must not leak onto the
+    # pitched part (which would force the whole pitched roof to U=2.30).
+    roofs = [
+        _Desc("Pitched, insulated (assumed)"),
+        _Desc("Flat, no insulation"),
+        _Desc("Roof room(s), no insulation (assumed)"),
+    ]
+
+    # Act
+    pitched, flat = _main_roof_descriptions_by_kind(roofs)
+
+    # Assert — RR dropped; flat and pitched kept apart.
+    assert pitched == "Pitched, insulated (assumed)"
+    assert flat == "Flat, no insulation"
+
+
+def test_mixed_flat_pitched_roof_does_not_contaminate_pitched_u_value() -> None:
+    # Arrange — 2-part dwelling: a 100 m² pitched insulated-assumed main
+    # roof (U=0.40) + a 2 m² flat uninsulated extension (U=2.30). Before the
+    # per-kind split, the joined "Pitched, insulated (assumed) | Flat, no
+    # insulation" description leaked the flat's "no insulation" onto the
+    # pitched part, billing the WHOLE roof at 2.30 (100×2.30 + 2×2.30 =
+    # 234.6 W/K). Correct: 100×0.40 + 2×2.30 = 44.6 W/K. Mirrors corpus
+    # cert 100010129331 (roof 110.5 -> 31.3 W/K, +13 -> 0 SAP).
+    main = make_building_part(
+        identifier=BuildingPartIdentifier.MAIN,
+        construction_age_band="C",
+        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,
+            ),
+        ],
+    )
+    ext = make_building_part(
+        identifier=BuildingPartIdentifier.EXTENSION_1,
+        construction_age_band="C",
+        roof_construction=5,
+        floor_dimensions=[
+            make_floor_dimension(
+                total_floor_area_m2=2.0, room_height_m=2.5,
+                party_wall_length_m=0.0, heat_loss_perimeter_m=6.0, floor=0,
+            ),
+        ],
+    )
+    ext.roof_construction_type = "Flat"
+    epc = make_minimal_sap10_epc(
+        total_floor_area_m2=102.0,
+        country_code="ENG",
+        sap_building_parts=[main, ext],
+    )
+    epc.roofs = [
+        EnergyElement(
+            description="Pitched, insulated (assumed)",
+            energy_efficiency_rating=4, environmental_efficiency_rating=4,
+        ),
+        EnergyElement(
+            description="Flat, no insulation",
+            energy_efficiency_rating=1, environmental_efficiency_rating=1,
+        ),
+    ]
+
+    # Act
+    result = heat_transmission_from_cert(epc)
+
+    # Assert — pitched main billed at its insulated U, not the flat's 2.30.
+    assert abs(result.roof_w_per_k - 44.6) <= 2.0
+
+
 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
diff --git a/tests/domain/sap10_calculator/worksheet/test_section_cascade_pins.py b/tests/domain/sap10_calculator/worksheet/test_section_cascade_pins.py
index 4e7336e3..6547a585 100644
--- a/tests/domain/sap10_calculator/worksheet/test_section_cascade_pins.py
+++ b/tests/domain/sap10_calculator/worksheet/test_section_cascade_pins.py
@@ -45,6 +45,7 @@ from tests.domain.sap10_calculator.worksheet import (
     _elmhurst_worksheet_001431_case6 as _w001431_case6,
     _elmhurst_worksheet_001431_case21 as _w001431_case21,
     _elmhurst_worksheet_001431_case43 as _w001431_case43,
+    _elmhurst_worksheet_001431_case44 as _w001431_case44,
 )
 
 
@@ -370,6 +371,126 @@ def test_case43_detailed_rr_dryline_and_mixed_roof_match_pdf() -> None:
     )
 
 
+def test_case44_non_separated_conservatory_fabric_matches_pdf() -> None:
+    """§3 fabric pin for simulated case 44 — a non-separated DOUBLE-glazed
+    conservatory (RdSAP 10 §6.1 + Table 25). The conservatory's glazed wall
+    bills as a window (27), its glazed roof as a rooflight (27a), its floor
+    adds a ground-loss term (28a), and its glazed wall + roof + floor areas
+    join (31)/(36); TFA (4) and volume (5) absorb its floor area + volume.
+    The main dwelling's walls (29a) / roof (30) are untouched — pinned to
+    guard against the conservatory leaking into the wrong element."""
+    # Arrange
+    epc = _w001431_case44.build_epc()
+
+    # Act
+    ht = heat_transmission_section_from_cert(epc)
+    dim = dimensions_from_cert(epc)
+
+    # Assert — §1 totals + §3 fabric, each at abs=1e-4.
+    _pin(dim.total_floor_area_m2, _w001431_case44.LINE_4_TFA_M2, "§1 (4) case44")
+    _pin(dim.volume_m3, _w001431_case44.LINE_5_VOLUME_M3, "§1 (5) case44")
+    _pin(
+        ht.windows_w_per_k,
+        _w001431_case44.LINE_27_WINDOWS_W_PER_K,
+        "§3 (27) case44",
+    )
+    _pin(
+        ht.roof_windows_w_per_k,
+        _w001431_case44.LINE_27A_ROOF_WINDOWS_W_PER_K,
+        "§3 (27a) case44",
+    )
+    _pin(
+        ht.floor_w_per_k,
+        _w001431_case44.LINE_28A_FLOOR_W_PER_K,
+        "§3 (28a) case44",
+    )
+    _pin(
+        ht.walls_w_per_k,
+        _w001431_case44.LINE_29A_WALLS_W_PER_K,
+        "§3 (29a) case44",
+    )
+    _pin(ht.roof_w_per_k, _w001431_case44.LINE_30_ROOF_W_PER_K, "§3 (30) case44")
+    _pin(
+        ht.total_external_element_area_m2,
+        _w001431_case44.LINE_31_EXTERNAL_AREA_M2,
+        "§3 (31) case44",
+    )
+    _pin(
+        ht.fabric_heat_loss_w_per_k,
+        _w001431_case44.LINE_33_FABRIC_W_PER_K,
+        "§3 (33) case44",
+    )
+    _pin(
+        ht.thermal_bridging_w_per_k,
+        _w001431_case44.LINE_36_THERMAL_BRIDGING_W_PER_K,
+        "§3 (36) case44",
+    )
+
+
+def test_case44_conservatory_demand_side_matches_pdf() -> None:
+    """End-to-end §6.1 conservatory demand pin for simulated case 44.
+    Beyond the §3 fabric, the conservatory ripples through the demand
+    cascade: its floor area enters TFA (4) → occupancy → §5 internal
+    gains (73); its glazing contributes §6 solar gains (83) at the
+    default E/W flux (Table 25 g=0.76, FF=0.70, 20° roof pitch); fabric
+    + ventilation + gains combine into the §7 useful gains (95) and the
+    space-heating demand (99). Every line ref reproduces the P960 to 1e-4.
+
+    The full SAP/CO2 is NOT asserted: the case-44 Summary omits the
+    House-Coal secondary heater the P960 carries (see the provider's NB) —
+    a Summary-input defect downstream of, and independent of, §6.1."""
+    # Arrange
+    epc = _w001431_case44.build_epc()
+
+    # Act
+    ig = internal_gains_section_from_cert(epc)
+    sg = solar_gains_section_from_cert(epc)
+    sh = space_heating_section_from_cert(epc)
+    assert ig is not None  # TFA present ⇒ §5 helper returns a result
+
+    # Assert — §5/§6/§7 demand line refs, each at abs=1e-4.
+    _pin(
+        ig.total_internal_gains_monthly_w[0],
+        _w001431_case44.LINE_73_INTERNAL_GAINS_JAN_W,
+        "§5 (73) case44",
+    )
+    _pin(
+        sg.total_solar_gains_monthly_w[0],
+        _w001431_case44.LINE_83_SOLAR_GAINS_JAN_W,
+        "§6 (83) case44",
+    )
+    _pin(
+        sh.useful_gains_monthly_w[0],
+        _w001431_case44.LINE_95_USEFUL_GAINS_JAN_W,
+        "§7 (95) case44",
+    )
+    _pin(
+        sh.space_heating_per_m2_kwh,
+        _w001431_case44.LINE_99_SPACE_HEATING_PER_M2_KWH,
+        "§7 (99) case44",
+    )
+
+
+def test_case44_blower_door_pressure_test_matches_pdf() -> None:
+    """Simulated case 44 lodges a Blower Door air-pressure test
+    (§12.2 "Pressure Test Result (AP50) 4.50"). SAP 10.2 §2 (17)-(18):
+    the AP50 reading routes infiltration via `(18) = AP50/20 + (8)` =
+    4.5/20 + 0.1167 = 0.3417, in preference to the components-based (16)
+    estimate. The extractor previously read only the AP4 (Pulse) column,
+    so a Blower Door result fell through to the structural-infiltration
+    default (effective ach 0.81 vs the worksheet's 0.58 → ventilation
+    heat loss over-counted by ~38%)."""
+    # Arrange
+    epc = _w001431_case44.build_epc()
+
+    # Act
+    vent = ventilation_from_cert(epc)
+
+    # Assert — (18) infiltration + (25) Jan effective ach, at abs=1e-4.
+    _pin(vent.pressure_test_ach, 0.3417, "§2 (18) case44")
+    _pin(vent.effective_monthly_ach[0], 0.5812, "§2 (25) Jan case44")
+
+
 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
diff --git a/tests/infrastructure/epc_client/test_sap_accuracy_corpus.py b/tests/infrastructure/epc_client/test_sap_accuracy_corpus.py
index aa05c9af..9aed0f34 100644
--- a/tests/infrastructure/epc_client/test_sap_accuracy_corpus.py
+++ b/tests/infrastructure/epc_client/test_sap_accuracy_corpus.py
@@ -95,10 +95,34 @@ _CORPUS = Path(
 # 67.3% -> 67.5% (MAE 1.020 -> 0.987). The follow-on `common_wall_*` Detailed-RR
 # surfaces (billed at main-wall U, deducted from the §3.10.1 residual) took the
 # 6-cert detailed-common-wall cohort 2.43 -> 1.25; corpus -> 67.6% (MAE 0.979).
-_MIN_WITHIN_HALF_SAP = 0.67
-_MAX_SAP_MAE = 0.99
-_MAX_CO2_MAE_TONNES = 0.35      # t CO2 / yr vs co2_emissions_current
-_MAX_PE_PER_M2_MAE = 16.0       # kWh / m2 / yr vs energy_consumption_current
+# The §3.9.2 Simplified Type-2 RR mapper (room_in_roof_type_2: gable quadratic +
+# common-wall L×(0.25+H), MIRRORING the worksheet-validated Summary path,
+# cross-mapper-parity-exact on cert 000565) -> 67.9% (MAE 0.959).
+# The §6.1 non-separated conservatory mapper (the gov API's glazed building
+# part → SapConservatory → §6.1 window/rooflight/floor cascade + TFA, MIRRORING
+# the case-44 Summary path pinned to 1e-4) -> 68.6% (MAE 0.942). 5 type-4
+# certs were over-rating (conservatory dropped → too little heat loss).
+# STONE WALL + INTERNAL/EXTERNAL INSULATION (RdSAP 10 §5.8 + Table 14, p.41-42):
+# the §5.8 added-insulation R-value adjustment was applied ONLY to WALL_SOLID_
+# BRICK; a stone (granite/sandstone) wall lodging wall_insulation_type 1/3 + a
+# thickness fell through the §5.6 branch and was billed at its UNINSULATED U
+# (e.g. sandstone 520 mm + 100 mm internal: 1.64 instead of 0.30 → 5× wall heat
+# loss). Mirroring the brick branch into the stone block recovered the worst of
+# the wall_insulation_type=3 under-rate cluster (cert 100052159386 -26.2 -> -4.1
+# SAP, walls 300 -> 55 W/K). within-0.5 68.6% -> 68.8% (MAE 0.942 -> 0.888;
+# PE MAE 14.3 -> 13.9; CO2 MAE 0.27 -> 0.26). Unit-pinned in test_rdsap_uvalues.
+# PER-PART ROOF DESCRIPTION (RdSAP 10 §5.11): the deduplicated epc.roofs[] list
+# was joined into ONE description fed to EVERY building part's u_roof, so a flat
+# "no insulation" extension dragged a pitched "insulated (assumed)" main roof to
+# the uninsulated 2.30 (3-part certs systematically under-rated: 56% within,
+# -0.79 mean). Matching each part to its own kind (flat vs pitched) fixed cert
+# 100010129331 (roof 110.5 -> 31.3 W/K, +13.1 -> -0.05 SAP). within-0.5
+# 68.8% -> 69.5% (MAE 0.888 -> 0.859; PE 13.9 -> 13.6); 3-part cohort 56% ->
+# 61%. Pinned in test_heat_transmission (by_kind split + no-contamination).
+_MIN_WITHIN_HALF_SAP = 0.69
+_MAX_SAP_MAE = 0.86
+_MAX_CO2_MAE_TONNES = 0.30      # t CO2 / yr vs co2_emissions_current
+_MAX_PE_PER_M2_MAE = 14.0       # kWh / m2 / yr vs energy_consumption_current
 
 
 def _load_corpus() -> list[dict[str, Any]]: