S0380.217: capture wall_insulation_thermal_conductivity (was dropped)

Second silently-dropped field from the 2130 audit: the schema-21
SapBuildingPart never declared `wall_insulation_thermal_conductivity`, so
`from_dict` discarded it. Captured it through schema 21.0.0/21.0.1 → domain
SapBuildingPart → API mapper, and wired it into u_wall's RdSAP 10 §5.8
documentary-evidence R-value calc (both the solid-brick §5.7/§5.8 path and
the cavity-composite path), replacing the bare 0.04 λ constant with a
resolved λ.

Resolver: absent / "Unknown" → the §5.8 default 0.04 W/m·K (mineral wool /
EPS); a mapped code → its λ; an unmapped integer code RAISES so the enum is
confirmed against a worksheet rather than silently mis-factored (same
incremental-coverage discipline as the glazing-type map). Only code 1
(= the default 0.04) is mapped — the sole observed value (cert 2130 Ext1).

Zero cascade effect today: the λ path fires only for solid-brick/cavity
walls with a *measured* wall thickness, and 2130 Ext1 lodges no wall
thickness, so its conductivity is captured-but-unused; all existing §5.8
certs lodge no conductivity → 0.04 default unchanged. The point is to stop
dropping lodged data and make λ correct when a future cert exercises it.

Suite: 2523 passed (1 pre-existing TFA fail); sap10_ml 237 passed (2
pre-existing stone-formula fails). Zero new pyright errors (46=46).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

datatypes/epc/domain/epc_property_data.py

@@ -477,6 +477,10 @@ class SapBuildingPart:
     # separate measured field), else the lodged string ("NI", a numeric
     # string, etc.). Mirrors `roof_insulation_thickness`.
     wall_insulation_thickness: Optional[Union[str, int]] = None
+    # RdSAP 10 §5.8 thermal-conductivity code for measured wall insulation
+    # (λ = 0.04 / 0.03 / 0.025 W/m·K). Used by the documentary-evidence
+    # R-value path when a measured wall thickness is lodged alongside it.
+    wall_insulation_thermal_conductivity: Optional[Union[str, int]] = None
     sap_alternative_wall_1: Optional[SapAlternativeWall] = None
     sap_alternative_wall_2: Optional[SapAlternativeWall] = None
 

datatypes/epc/domain/mapper.py

@@ -564,6 +564,9 @@ class EpcPropertyDataMapper:
                         bp.wall_insulation_thickness,
                         getattr(bp, "wall_insulation_thickness_measured", None),
                     ),
+                    wall_insulation_thermal_conductivity=getattr(
+                        bp, "wall_insulation_thermal_conductivity", None
+                    ),
                     floor_heat_loss=bp.floor_heat_loss,
                     floor_insulation_thickness=None,
                     roof_construction=bp.roof_construction,
@@ -700,6 +703,9 @@ class EpcPropertyDataMapper:
                         bp.wall_insulation_thickness,
                         getattr(bp, "wall_insulation_thickness_measured", None),
                     ),
+                    wall_insulation_thermal_conductivity=getattr(
+                        bp, "wall_insulation_thermal_conductivity", None
+                    ),
                     floor_heat_loss=bp.floor_heat_loss,
                     floor_insulation_thickness=None,
                     roof_construction=bp.roof_construction,
@@ -836,6 +842,9 @@ class EpcPropertyDataMapper:
                         bp.wall_insulation_thickness,
                         getattr(bp, "wall_insulation_thickness_measured", None),
                     ),
+                    wall_insulation_thermal_conductivity=getattr(
+                        bp, "wall_insulation_thermal_conductivity", None
+                    ),
                     floor_heat_loss=bp.floor_heat_loss,
                     # API certs commonly lodge "NI" (no measured
                     # thickness) on floors that aren't actually
@@ -998,6 +1007,9 @@ class EpcPropertyDataMapper:
                         bp.wall_insulation_thickness,
                         getattr(bp, "wall_insulation_thickness_measured", None),
                     ),
+                    wall_insulation_thermal_conductivity=getattr(
+                        bp, "wall_insulation_thermal_conductivity", None
+                    ),
                     floor_heat_loss=bp.floor_heat_loss,
                     # API certs commonly lodge "NI" (no measured
                     # thickness) on floors that aren't actually
@@ -1177,6 +1189,9 @@ class EpcPropertyDataMapper:
                         bp.wall_insulation_thickness,
                         getattr(bp, "wall_insulation_thickness_measured", None),
                     ),
+                    wall_insulation_thermal_conductivity=getattr(
+                        bp, "wall_insulation_thermal_conductivity", None
+                    ),
                     floor_heat_loss=bp.floor_heat_loss,
                     # API certs commonly lodge "NI" (no measured
                     # thickness) on floors that aren't actually
@@ -1397,6 +1412,9 @@ class EpcPropertyDataMapper:
                         bp.wall_insulation_thickness,
                         getattr(bp, "wall_insulation_thickness_measured", None),
                     ),
+                    wall_insulation_thermal_conductivity=getattr(
+                        bp, "wall_insulation_thermal_conductivity", None
+                    ),
                     floor_heat_loss=bp.floor_heat_loss,
                     # API certs commonly lodge "NI" (no measured
                     # thickness) on floors that aren't actually
@@ -1662,6 +1680,9 @@ class EpcPropertyDataMapper:
                         bp.wall_insulation_thickness,
                         getattr(bp, "wall_insulation_thickness_measured", None),
                     ),
+                    wall_insulation_thermal_conductivity=getattr(
+                        bp, "wall_insulation_thermal_conductivity", None
+                    ),
                     floor_heat_loss=bp.floor_heat_loss,
                     # API certs commonly lodge "NI" (no measured
                     # thickness) on floors that aren't actually

datatypes/epc/schema/rdsap_schema_21_0_0.py

@@ -246,6 +246,11 @@ class SapBuildingPart:
     # undeclared, so `from_dict` silently dropped it and the cascade fell
     # back to the 50 mm "insulation present, unknown thickness" default.
     wall_insulation_thickness_measured: Optional[Union[str, int]] = None
+    # Lodged thermal-conductivity code for measured wall insulation
+    # (RdSAP 10 §5.8: λ = 0.04 / 0.03 / 0.025 W/m·K). Previously undeclared
+    # → dropped by `from_dict`. Consumed by `u_wall`'s documentary-evidence
+    # R-value path when a measured wall thickness is also lodged.
+    wall_insulation_thermal_conductivity: Optional[Union[str, int]] = None
     floor_insulation_thickness: Optional[str] = None
     flat_roof_insulation_thickness: Optional[Union[str, int]] = None
 

datatypes/epc/schema/rdsap_schema_21_0_1.py

@@ -284,6 +284,11 @@ class SapBuildingPart:
     # undeclared, so `from_dict` silently dropped it and the cascade fell
     # back to the 50 mm "insulation present, unknown thickness" default.
     wall_insulation_thickness_measured: Optional[Union[str, int]] = None
+    # Lodged thermal-conductivity code for measured wall insulation
+    # (RdSAP 10 §5.8: λ = 0.04 / 0.03 / 0.025 W/m·K). Previously undeclared
+    # → dropped by `from_dict`. Consumed by `u_wall`'s documentary-evidence
+    # R-value path when a measured wall thickness is also lodged.
+    wall_insulation_thermal_conductivity: Optional[Union[str, int]] = None
     floor_insulation_thickness: Optional[str] = None
     flat_roof_insulation_thickness: Optional[Union[str, int]] = None
 

domain/sap10_calculator/worksheet/heat_transmission.py

@@ -750,6 +750,10 @@ def heat_transmission_from_cert(
                 # insulation_type combination doesn't match the formula
                 # path's preconditions.
                 wall_thickness_mm=part.wall_thickness_mm,
+                # RdSAP 10 §5.8 — lodged insulation thermal-conductivity
+                # code feeds the documentary-evidence R-value calc when a
+                # measured wall thickness is also present (else ignored).
+                wall_insulation_thermal_conductivity=part.wall_insulation_thermal_conductivity,
             )
         # When the per-bp `roof_insulation_thickness` is explicitly lodged
         # as 0 (uninsulated — e.g. cert 001479 Ext2 PS sloping ceiling

domain/sap10_ml/rdsap_uvalues.py

@@ -177,6 +177,43 @@ WALL_INSULATION_CAVITY_PLUS_INTERNAL: Final[int] = 7
 # (cavity + external/internal insulation).
 _WALL_INSULATION_LAMBDA_W_PER_MK: Final[float] = 0.04
 
+# RdSAP 10 §5.8 (page 41) — when documentary evidence lodges the insulation
+# thermal conductivity, the R-value calc uses it instead of the 0.04 default.
+# The spec offers three λ: 0.04 (mineral wool / EPS, the default), 0.03 (XPS),
+# 0.025 (PUR / PIR / phenolic). The GOV.UK API surfaces a coded value
+# (`wall_insulation_thermal_conductivity`); code 1 = the default 0.04 (the
+# only code observed — cert 2130 Ext1, whose documentary-evidence path does
+# not fire as no wall thickness is lodged, so the value is captured but
+# unused there). Other codes raise until a worksheet-backed fixture confirms
+# their λ — the same incremental-coverage discipline as the glazing-type map.
+_WALL_INSULATION_CONDUCTIVITY_CODE_TO_LAMBDA: Final[dict[int, float]] = {
+    1: 0.04,
+}
+
+
+def _resolve_wall_insulation_lambda_w_per_mk(
+    conductivity: "str | int | None",
+) -> float:
+    """Resolve the insulation λ (W/m·K) for the §5.8 documentary-evidence
+    R-value calc. Absent / "Unknown" → the 0.04 default; a mapped integer
+    code → its λ; an unmapped integer code raises so the enum is confirmed
+    against a worksheet rather than silently mis-factored."""
+    if conductivity is None:
+        return _WALL_INSULATION_LAMBDA_W_PER_MK
+    if isinstance(conductivity, str):
+        text = conductivity.strip()
+        if not text or text.lower() == "unknown" or not text.isdigit():
+            return _WALL_INSULATION_LAMBDA_W_PER_MK
+        conductivity = int(text)
+    lam = _WALL_INSULATION_CONDUCTIVITY_CODE_TO_LAMBDA.get(conductivity)
+    if lam is None:
+        raise ValueError(
+            "unmapped wall_insulation_thermal_conductivity code "
+            f"{conductivity!r}; add its RdSAP 10 §5.8 λ "
+            "(0.04 / 0.03 / 0.025 W/m·K) once a worksheet confirms it"
+        )
+    return lam
+
 # RdSAP10 §5.8 final note + Table 14 page 41: "For drylining including
 # laths and plaster use Rinsulation = 0.17 m²K/W." Applied additively to
 # the base U-value of an otherwise-uninsulated wall when the cert lodges
@@ -489,6 +526,7 @@ def u_wall(
     dry_lined: bool = False,
     curtain_wall_age: Optional[str] = None,
     wall_thickness_mm: Optional[int] = None,
+    wall_insulation_thermal_conductivity: "str | int | None" = None,
 ) -> float:
     """RdSAP10 wall U-value in W/m^2K, never null.
 
@@ -601,7 +639,10 @@ def u_wall(
     ):
         u0 = _u_brick_thin_wall_age_a_to_e(wall_thickness_mm)
         r_ins = _r_insulation_table_14(
-            insulation_thickness_mm, _WALL_INSULATION_LAMBDA_W_PER_MK,
+            insulation_thickness_mm,
+            _resolve_wall_insulation_lambda_w_per_mk(
+                wall_insulation_thermal_conductivity
+            ),
         )
         u_unrounded = 1.0 / (1.0 / u0 + r_ins)
         return float(
@@ -623,7 +664,9 @@ def u_wall(
         # for column alignment). Cascade-internal HLC then uses the
         # rounded U so net wall HLC matches `A × U_2dp` exactly.
         u_filled = _CAVITY_FILLED_ENG[age_idx]
-        r_ins = (insulation_thickness_mm / 1000.0) / _WALL_INSULATION_LAMBDA_W_PER_MK
+        r_ins = (insulation_thickness_mm / 1000.0) / _resolve_wall_insulation_lambda_w_per_mk(
+            wall_insulation_thermal_conductivity
+        )
         u_unrounded = 1.0 / (1.0 / u_filled + r_ins)
         # Half-up 2-d.p. round so 0.2545 → 0.25, matching the dr87
         # worksheet's column-display behaviour (used downstream in A×U).

domain/sap10_ml/tests/test_rdsap_uvalues.py

@@ -1870,3 +1870,59 @@ def test_u_floor_matches_section_5_12_formula_for_cohort_geometry(
 
     # Assert
     assert abs(u - expected_u) < 1e-4
+
+
+def test_resolve_wall_insulation_lambda_absent_uses_default() -> None:
+    # Arrange — no lodged conductivity → RdSAP 10 §5.8 default 0.04 W/m·K.
+    from domain.sap10_ml.rdsap_uvalues import (
+        _resolve_wall_insulation_lambda_w_per_mk,
+    )
+
+    # Act
+    lam = _resolve_wall_insulation_lambda_w_per_mk(None)
+
+    # Assert
+    assert abs(lam - 0.04) <= 1e-9
+
+
+def test_resolve_wall_insulation_lambda_unknown_string_uses_default() -> None:
+    # Arrange — a non-numeric "Unknown" lodgement defers to the default.
+    from domain.sap10_ml.rdsap_uvalues import (
+        _resolve_wall_insulation_lambda_w_per_mk,
+    )
+
+    # Act
+    lam = _resolve_wall_insulation_lambda_w_per_mk("Unknown")
+
+    # Assert
+    assert abs(lam - 0.04) <= 1e-9
+
+
+def test_resolve_wall_insulation_lambda_code_1_is_default_mineral_wool() -> None:
+    # Arrange — code 1 = the §5.8 default λ=0.04 (mineral wool / EPS);
+    # cert 2130 Ext1 lodges this. Numeric-string form resolves identically.
+    from domain.sap10_ml.rdsap_uvalues import (
+        _resolve_wall_insulation_lambda_w_per_mk,
+    )
+
+    # Act
+    lam_int = _resolve_wall_insulation_lambda_w_per_mk(1)
+    lam_str = _resolve_wall_insulation_lambda_w_per_mk("1")
+
+    # Assert
+    assert abs(lam_int - 0.04) <= 1e-9
+    assert abs(lam_str - 0.04) <= 1e-9
+
+
+def test_resolve_wall_insulation_lambda_unmapped_code_raises() -> None:
+    # Arrange — an unmapped code must raise (incremental-coverage gate)
+    # rather than silently mis-factor the R-value.
+    import pytest as _pytest
+
+    from domain.sap10_ml.rdsap_uvalues import (
+        _resolve_wall_insulation_lambda_w_per_mk,
+    )
+
+    # Act / Assert
+    with _pytest.raises(ValueError):
+        _resolve_wall_insulation_lambda_w_per_mk(2)