Slice S0380.85: Curtain Wall §5.18 dispatch closes BP[2] Ext2 cascade gap

RdSAP 10 §5.18 (PDF p.48) "Curtain wall - U-value and other parameters":

  "If documentary evidence is available, use calculated U-value of the
   whole curtain wall. Otherwise for the purpose of RdSAP, U= 2.0 W/m²K
   for pre-2023 curtain walls, And for post-2023 (2024 in Scotland)
   U-values as for windows given in Notes below Table 24."

Table 24 row "Double or triple glazed England/Wales: 2022 or later"
PVC/wood column = 1.4 W/m²K. Whole-wall curtain walls use Frame
Factor=1 per the §5.18 closer.

Pre-S0380.85 `WALL_CURTAIN=9` was defined at rdsap_uvalues.py:116 but
NOT included in `known_types`, so `u_wall(construction=9)` fell through
to `_DEFAULT_WALL_BY_AGE.get(band, WALL_CAVITY)` → cavity table at age
H = 0.60. Cert 000565 BP[2] Ext2 lodges `Type: CW Curtain Wall` +
`Curtain Wall Age: Post 2023` per Summary PDF §7; worksheet pins U=1.40
(matching the §5.18 Post-2023 PVC/wood row). Cascade under-counted
walls by Δ U=0.80 × area = −112.2 W/K on this BP — 70% of the
post-S0380.84 BP main-wall residual (−161 W/K total).

§5.18 keys the curtain-wall U-value on the per-BP installation age,
NOT on the dwelling-wide `construction_age_band` — cert 000565 is
age H (1991-1995) but the curtain wall itself was installed
Post-2023. Plumb a new optional field through the extractor → datatype
→ mapper → cascade so the §5.18 dispatch sees it.

Files touched (5-layer slice span):

  - backend/documents_parser/elmhurst_extractor.py:
      `_wall_details_from_lines` reads "Curtain Wall Age" via
      `_local_val` so absent lines stay None (not "").
  - datatypes/epc/surveys/elmhurst_site_notes.py:WallDetails:
      `curtain_wall_age: Optional[str] = None` field added.
  - datatypes/epc/domain/epc_property_data.py:SapBuildingPart:
      `curtain_wall_age: Optional[str] = None` field added.
  - datatypes/epc/domain/mapper.py:_map_elmhurst_building_part:
      threads `walls.curtain_wall_age` onto SapBuildingPart.
  - domain/sap10_ml/rdsap_uvalues.py:
      new `_u_curtain_wall(curtain_wall_age)` helper + WALL_CURTAIN
      dispatch in `u_wall` before the `known_types` lookup.
      "Post 2023" / "Post-2023" → 1.4; everything else (incl. None)
      → 2.0 per §5.18 fallback.
  - domain/sap10_calculator/worksheet/heat_transmission.py:
      passes `curtain_wall_age=part.curtain_wall_age` to `u_wall`
      on the main-wall path. (Alt-wall path unchanged — cert 000565
      lodges CW only as a main wall, never as an alt sub-area; alt
      coverage is a follow-up slice if a future cert exercises it.)

Tests (6 new, AAA-structure):

  - 3 in domain/sap10_ml/tests/test_rdsap_uvalues.py — `u_wall` direct
    unit tests for Post 2023 (1.4), Pre 2023 (2.0), and absent
    lodging fallback (2.0).
  - 3 in backend/documents_parser/tests/test_summary_pdf_mapper_chain
    .py — extractor pin (BP[2] Ext2 surfaces "Post 2023", non-CW BPs
    stay None), mapper pin (curtain_wall_age threaded to BP[2]
    SapBuildingPart), cascade pin (`heat_transmission_from_cert`
    walls subtotal ≥ 540 W/K — pre-S0380.85 was 443).

Cert 000565 cascade walls: 443 → 555.93 W/K (worksheet 604.07; 70%
closer). Test baseline: 558 pass (was 555 + 3 new) + 9 expected
`test_sap_result_pin[000565-*]` fails unchanged.

Per [[feedback-verify-handover-claims]]: the post-S0380.84 handover
predicted SH residual would close +2591 → ~+800 kWh after this slice,
but the cascade is actually OVER-counting SH despite walls being
UNDER-counted. Closing the wall under-count makes the SH residual
*larger* (+2591 → +6348). The wall fix is spec-correct; the SH
over-count is a separate channel that surfaces more sharply now. Per
[[feedback-spec-citation-in-commits]] + [[feedback-spec-floor-skepticism]]
+ the S0380.84 precedent, ship the spec-correct change and document
the surfaced gap for the next slice rather than reverting to the
compensating-bugs state.

Pyright net-zero on every touched file (existing pre-existing errors
unchanged). Cohort + golden + cert 9501 unaffected — curtain_wall_age
defaults to None on those certs and `u_wall` ignores it unless
`construction == WALL_CURTAIN`.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/documents_parser/elmhurst_extractor.py

@@ -268,6 +268,14 @@ class ElmhurstSiteNotesExtractor:
             thickness_mm=thickness_mm,
             insulation_thickness_mm=insulation_thickness_mm,
             alternative_walls=self._alternative_walls_from_lines(lines),
+            # Summary §7 lodges the per-BP "Curtain Wall Age" line only
+            # when `Type: CW Curtain Wall`. Per RdSAP 10 §5.18 (PDF
+            # p.48) this drives the curtain-wall U-value (Post 2023 →
+            # 1.4; Pre 2023 → 2.0) independent of the dwelling-wide
+            # age band. Use `_local_val` (Optional[str]) so absent
+            # lines surface as None, not the empty-string sentinel
+            # `_local_str` returns.
+            curtain_wall_age=self._local_val(lines, "Curtain Wall Age"),
         )
 
     def _alternative_walls_from_lines(self, lines: List[str]) -> List[AlternativeWall]:

backend/documents_parser/tests/test_summary_pdf_mapper_chain.py

@@ -1340,6 +1340,126 @@ def test_summary_000565_ext3_ext4_wall_constructions_route_to_basement_code_6()
     assert epc.sap_building_parts[4].main_wall_is_basement is True
 
 
+def test_summary_000565_extractor_finds_curtain_wall_age_post_2023_on_bp_2_ext2() -> None:
+    """Summary §7 per-BP Wall block carries a `Curtain Wall Age` line
+    when `Type: CW Curtain Wall` is lodged. Cert 000565 Ext2 (BP[2])
+    is the cohort fixture: it lodges
+
+        Type CW Curtain Wall
+        Curtain Wall Age Post 2023
+        U-value Known No
+
+    Per RdSAP 10 §5.18 (PDF p.48), the U-value of a curtain wall is
+    keyed on the per-BP `Curtain Wall Age` (Post 2023 → Table 24
+    window row; Pre 2023 → 2.0 W/m²K), NOT on the dwelling-wide
+    `construction_age_band`. The extractor must surface this field
+    so the mapper + cascade can dispatch correctly. Pre-S0380.85 the
+    line was silently dropped and `wall_construction=9` fell through
+    to the cavity-default Table 6 row.
+
+    Pure extractor data-completion step — downstream cascade impact
+    lands when the mapper threads the new field through and `u_wall`
+    grows a Curtain Wall branch (follow-up sub-step in the same slice).
+    """
+    # Arrange
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_000565_PDF)
+
+    # Act
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+
+    # Assert — BP[2] is Ext2 (index 1 in `extensions`).
+    ext2_walls = site_notes.extensions[1].walls
+    assert ext2_walls.wall_type == "CW Curtain Wall", (
+        f"Ext2 wall_type = {ext2_walls.wall_type!r}; expected 'CW Curtain Wall'"
+    )
+    assert ext2_walls.curtain_wall_age == "Post 2023", (
+        f"Ext2 curtain_wall_age = {ext2_walls.curtain_wall_age!r}; "
+        f"expected 'Post 2023'"
+    )
+    # Negative case — BPs without Curtain Wall don't have a Curtain
+    # Wall Age line; the field must be None (not the empty-string
+    # sentinel `_local_str` returns).
+    main_walls = site_notes.walls
+    assert main_walls.curtain_wall_age is None, (
+        f"Main wall (non-CW) curtain_wall_age = "
+        f"{main_walls.curtain_wall_age!r}; expected None"
+    )
+
+
+def test_summary_000565_mapper_threads_curtain_wall_age_post_2023_to_bp_2_sap_building_part() -> None:
+    """The Elmhurst mapper builds a `SapBuildingPart` per BP from the
+    extracted `WallDetails`. `curtain_wall_age` must be threaded
+    through so the heat-transmission cascade can dispatch on it (per
+    [[reference-unmapped-api-code]] strict-plumbing pattern). Cert
+    000565 BP[2] Ext2 is the fixture: `wall_construction=9`
+    (WALL_CURTAIN) + `curtain_wall_age="Post 2023"`.
+
+    Per RdSAP 10 §5.18 + §1.5: a curtain wall can be a main wall, an
+    alt wall, or absorbed into the prevailing wall when <10% area.
+    This slice scopes to the main-wall path (cert 000565 lodges CW
+    only as the BP[2] main wall, never as an alt sub-area).
+    """
+    # Arrange
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_000565_PDF)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+
+    # Act
+    epc = EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)
+
+    # Assert
+    bp_2 = epc.sap_building_parts[2]
+    assert bp_2.wall_construction == 9, (
+        f"BP[2] wall_construction = {bp_2.wall_construction!r}; "
+        f"expected 9 (WALL_CURTAIN)"
+    )
+    assert bp_2.curtain_wall_age == "Post 2023", (
+        f"BP[2] curtain_wall_age = {bp_2.curtain_wall_age!r}; "
+        f"expected 'Post 2023'"
+    )
+    # Non-CW BPs preserve curtain_wall_age=None (no per-BP signal).
+    assert epc.sap_building_parts[0].curtain_wall_age is None
+    assert epc.sap_building_parts[1].curtain_wall_age is None
+
+
+def test_summary_000565_ext2_curtain_wall_routes_to_u_value_1p4_per_rdsap_10_section_5_18() -> None:
+    """End-to-end cascade pin: with `curtain_wall_age="Post 2023"` plumbed
+    through extractor + mapper + `u_wall` `WALL_CURTAIN` branch, the
+    `heat_transmission_from_cert` walls subtotal on cert 000565 must
+    reflect the §5.18 Curtain Wall U=1.4 W/m²K on BP[2] Ext2.
+
+    Pre-S0380.85: BP[2] cascade U=0.60 (Cavity default, age H), Δ −0.80
+    W/m²K vs worksheet U=1.40. The BP[2] Ext2 gross wall area on cert
+    000565 multiplied by this U-delta accounts for the documented
+    −112.2 W/K contribution to the walls subtotal residual.
+
+    Asserts the cascade walls subtotal moves materially toward the
+    worksheet target 604.07 W/K (from pre-S0380.85's 443 W/K). The
+    remaining ~50 W/K gap is the BP[0] Main alt1 thin-wall stone
+    granite cascade gap — out of scope for this slice; closes in
+    follow-up S0380.86.
+    """
+    # Arrange
+    from domain.sap10_calculator.worksheet.heat_transmission import (
+        heat_transmission_from_cert,
+    )
+
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_000565_PDF)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+    epc = EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)
+
+    # Act
+    ht = heat_transmission_from_cert(epc)
+
+    # Assert — pre-S0380.85 cascade had walls 443 W/K. Curtain Wall
+    # closure adds ~112 W/K (worksheet target 604 W/K). Lower-bound
+    # 540 W/K is a robust gate that still leaves headroom for the
+    # remaining BP[0] alt1 thin-wall gap; the cascade reaches ~555.
+    assert ht.walls_w_per_k >= 540.0, (
+        f"walls_w_per_k = {ht.walls_w_per_k:.2f}; expected ≥540 after "
+        f"Curtain Wall §5.18 dispatch (pre-S0380.85 baseline was 443)"
+    )
+
+
 def test_summary_000565_ext1_party_wall_routes_to_cavity_filled_code_4() -> None:
     # Arrange — RdSAP 10 Table 15 row 3 "Cavity masonry filled":
     # cert 000565 Ext1 lodges "CF Cavity masonry filled". Routes

datatypes/epc/domain/epc_property_data.py

@@ -435,6 +435,13 @@ class SapBuildingPart:
         None  # TODO: make enum/mapping?
     )
     sap_room_in_roof: Optional[SapRoomInRoof] = None
+    # Per RdSAP 10 §5.18 (PDF p.48), a curtain wall (wall_construction
+    # =WALL_CURTAIN=9) takes its U-value from the per-BP installation
+    # age — "Post 2023" routes to the Table 24 window row (1.4 W/m²K
+    # PVC/wood), anything else (incl. None) defaults to U=2.0 W/m²K.
+    # The dwelling-wide `construction_age_band` does NOT govern curtain
+    # walls; this field decouples them per spec.
+    curtain_wall_age: Optional[str] = None
 
     @property
     def main_wall_is_basement(self) -> bool:

datatypes/epc/domain/mapper.py

@@ -3121,6 +3121,12 @@ def _map_elmhurst_building_part(
         sap_room_in_roof=room_in_roof,
         sap_alternative_wall_1=alt_walls[0],
         sap_alternative_wall_2=alt_walls[1],
+        # RdSAP 10 §5.18 (PDF p.48) — curtain-wall U-value is keyed on
+        # the per-BP `Curtain Wall Age` lodging, not on the dwelling-
+        # wide age band. Thread the extractor's optional field through
+        # so heat_transmission's `u_wall(curtain_wall_age=...)` can
+        # dispatch. None for non-curtain-wall BPs.
+        curtain_wall_age=walls.curtain_wall_age,
     )
 
 

datatypes/epc/surveys/elmhurst_site_notes.py

@@ -89,6 +89,13 @@ class WallDetails:
     # "Insulation Thickness" / "100 mm" line pair when a composite or
     # retrofit insulation is recorded. None when the PDF omits the line.
     insulation_thickness_mm: Optional[int] = None
+    # Per-BP curtain-wall installation age, lodged in Summary §7 as
+    # "Curtain Wall Age" when `wall_type` is "CW Curtain Wall". Per
+    # RdSAP 10 §5.18 (PDF p.48) the curtain-wall U-value keys on this
+    # field (Post 2023 → Table 24 window row; Pre 2023 → 2.0 W/m²K),
+    # NOT on the dwelling-wide `construction_age_band`. None when the
+    # BP is not a curtain wall.
+    curtain_wall_age: Optional[str] = None
 
 
 @dataclass

domain/sap10_calculator/worksheet/heat_transmission.py

@@ -647,6 +647,11 @@ def heat_transmission_from_cert(
                 insulation_present=wall_ins_present,
                 description=wall_description,
                 wall_insulation_type=wall_ins_type,
+                # RdSAP 10 §5.18 (PDF p.48) — curtain walls dispatch
+                # on the per-BP installation age, not the dwelling age
+                # band. None for non-curtain-wall parts (ignored by
+                # `u_wall` unless wall_construction == WALL_CURTAIN).
+                curtain_wall_age=part.curtain_wall_age,
             )
         # When the per-bp `roof_insulation_thickness` is explicitly lodged
         # as 0 (uninsulated — e.g. cert 001479 Ext2 PS sloping ceiling

domain/sap10_ml/rdsap_uvalues.py

@@ -144,6 +144,39 @@ _WALL_INSULATION_LAMBDA_W_PER_MK: Final[float] = 0.04
 _DRY_LINING_RESISTANCE_M2K_PER_W: Final[float] = 0.17
 
 
+# RdSAP 10 §5.18 (PDF p.48) — curtain-wall U-values.
+#
+#   "If documentary evidence is available, use calculated U-value of the
+#    whole curtain wall. Otherwise for the purpose of RdSAP, U= 2.0 W/m²K
+#    for pre-2023 curtain walls, And for post-2023 (2024 in Scotland)
+#    U-values as for windows given in Notes below Table 24."
+#
+# Table 24 row "Double or triple glazed, England/Wales: 2022 or later"
+# is the matching post-2023 row: U = 1.4 (PVC/wood) / 1.6 (metal). The
+# Frame Factor for a whole-wall curtain wall is 1 per the §5.18 closer.
+#
+# Empirical pin: cert 000565 BP[2] Ext2 lodges `Curtain Wall Age: Post
+# 2023` and the U985 worksheet uses U=1.40 for this BP — matching the
+# PVC/wood row (the §5.18 default since curtain-wall frame material is
+# not separately surfaced on the Elmhurst Summary).
+_CURTAIN_WALL_U_PRE_2023: Final[float] = 2.0
+_CURTAIN_WALL_U_POST_2023: Final[float] = 1.4
+_CURTAIN_WALL_POST_2023_LODGEMENTS: Final[frozenset[str]] = frozenset({
+    "Post 2023",
+    "Post-2023",
+})
+
+
+def _u_curtain_wall(curtain_wall_age: Optional[str]) -> float:
+    """RdSAP 10 §5.18 curtain-wall U-value. Keyed on the per-BP
+    `Curtain Wall Age` lodgement (Summary §7), NOT on the dwelling-wide
+    `construction_age_band`. Unknown / absent → pre-2023 default per
+    the spec's "U= 2.0 W/m²K for pre-2023 curtain walls" sentence."""
+    if curtain_wall_age is not None and curtain_wall_age.strip() in _CURTAIN_WALL_POST_2023_LODGEMENTS:
+        return _CURTAIN_WALL_U_POST_2023
+    return _CURTAIN_WALL_U_PRE_2023
+
+
 _AGE_BANDS: Final[tuple[str, ...]] = tuple("ABCDEFGHIJKLM")
 
 
@@ -336,6 +369,7 @@ def u_wall(
     description: Optional[str] = None,
     wall_insulation_type: Optional[int] = None,
     dry_lined: bool = False,
+    curtain_wall_age: Optional[str] = None,
 ) -> float:
     """RdSAP10 wall U-value in W/m^2K, never null.
 
@@ -361,12 +395,23 @@ def u_wall(
     insulation stack. Cohort fixture: cert 7700 Alt 1 cavity-as-built
     age C with Dry-lining: Yes — base U=1.5 → adjusted U=1.20 (2 d.p.,
     matching worksheet `CavityWallPlasterOnDabsDenseBlock`).
+
+    `curtain_wall_age` keys the RdSAP 10 §5.18 (PDF p.48) curtain-wall
+    dispatch. Applies only when `construction == WALL_CURTAIN`; ignored
+    for all other constructions. The dwelling-wide `age_band` does NOT
+    govern curtain walls per §5.18 — the installation age does.
     """
     measured = _measured_u_from_description(description)
     if measured is not None:
         return measured
     if country is None and age_band is None and construction is None and insulation_thickness_mm is None and not insulation_present:
         return 1.5
+    # RdSAP 10 §5.18 (PDF p.48) — curtain walls bypass the Table 6/7/8/9
+    # cascade entirely; their U-value keys solely on the per-BP
+    # `Curtain Wall Age` lodging. Place the dispatch before `known_types`
+    # so an explicit `construction=WALL_CURTAIN` always routes here.
+    if construction == WALL_CURTAIN:
+        return _u_curtain_wall(curtain_wall_age)
     ctry = country if country is not None else Country.ENG
     age_idx = _age_index(age_band)
     band = _AGE_BANDS[age_idx]

domain/sap10_ml/tests/test_rdsap_uvalues.py

@@ -23,6 +23,7 @@ import pytest
 from domain.sap10_ml.rdsap_uvalues import (
     Country,
     WALL_CAVITY,
+    WALL_CURTAIN,
     WALL_INSULATION_FILLED_CAVITY,
     WALL_SOLID_BRICK,
     WALL_STONE_GRANITE,
@@ -537,6 +538,75 @@ def test_u_wall_uses_rdsap_unknown_thickness_default_of_50mm_when_insulated_but_
     assert result == pytest.approx(0.35, abs=0.001)
 
 
+def test_u_wall_curtain_wall_post_2023_routes_to_window_table_24_u_1p4_per_rdsap_5_18() -> None:
+    # Arrange — RdSAP 10 §5.18 (PDF p.48): "Otherwise for the purpose of
+    # RdSAP, U= 2.0 W/m²K for pre-2023 curtain walls, And for post-2023
+    # (2024 in Scotland) U-values as for windows given in Notes below
+    # Table 24." Table 24 row "Double or triple glazed England/Wales:
+    # 2022 or later" PVC/wood column = 1.4 W/m²K. Cert 000565 BP[2]
+    # Ext2 lodges `Type: CW Curtain Wall` + `Curtain Wall Age: Post 2023`
+    # — worksheet pins U=1.40 for this BP.
+    #
+    # Pre-S0380.85: `WALL_CURTAIN=9` was defined but not in `known_types`
+    # at u_wall:373-376, so the dispatch fell through to
+    # `_DEFAULT_WALL_BY_AGE.get(band, WALL_CAVITY)` → cavity table at age
+    # H = 0.60. Cascade walls subtotal under-counted by ~112 W/K on
+    # this BP.
+
+    # Act
+    result = u_wall(
+        country=Country.ENG,
+        age_band="H",
+        construction=WALL_CURTAIN,
+        insulation_thickness_mm=None,
+        curtain_wall_age="Post 2023",
+    )
+
+    # Assert
+    assert abs(result - 1.4) <= 1e-9
+
+
+def test_u_wall_curtain_wall_pre_2023_uses_rdsap_5_18_default_u_2p0() -> None:
+    # Arrange — RdSAP 10 §5.18 (PDF p.48) fallback for curtain walls
+    # built before 2023 (or installed-age unknown): U = 2.0 W/m²K.
+    # Independent of construction age band — §5.18 keys solely on the
+    # curtain-wall-age lodging (Post 2023 vs everything else), not on
+    # the dwelling-wide `construction_age_band`.
+
+    # Act
+    result = u_wall(
+        country=Country.ENG,
+        age_band="H",
+        construction=WALL_CURTAIN,
+        insulation_thickness_mm=None,
+        curtain_wall_age="Pre 2023",
+    )
+
+    # Assert
+    assert abs(result - 2.0) <= 1e-9
+
+
+def test_u_wall_curtain_wall_missing_age_lodgement_defaults_to_pre_2023_u_2p0_per_rdsap_5_18() -> None:
+    # Arrange — when the cert lodges `Type: CW Curtain Wall` but no
+    # `Curtain Wall Age` line (older Elmhurst Summary PDFs, or API EPCs
+    # without the per-BP curtain_wall_age field), apply the §5.18
+    # default. The §5.18 sentence "U= 2.0 W/m²K for pre-2023 curtain
+    # walls" applies as the unknown-age fallback — matches the spec's
+    # "assume as-built" convention elsewhere in the cascade.
+
+    # Act
+    result = u_wall(
+        country=Country.ENG,
+        age_band="H",
+        construction=WALL_CURTAIN,
+        insulation_thickness_mm=None,
+        curtain_wall_age=None,
+    )
+
+    # Assert
+    assert abs(result - 2.0) <= 1e-9
+
+
 # ----- Roofs -----