slice S-B6: glazing g_perpendicular + frame_factor lookups (Tables 6b/6c)

Replaces the two hardcoded glazing defaults (g⊥=0.63, FF=0.7) in the
cert→inputs mapper with spec-driven lookups:

  - g_perpendicular by glazing_type (Table 6b):
      single → 0.85, double 2002+ → 0.72, low-E soft → 0.63,
      secondary → 0.76, triple → 0.68. Default 0.72 when missing.
  - frame_factor by frame_material (Table 6c):
      wood/PVC/composite → 0.70, aluminium/steel/metal → 0.83.

Measured values from window_transmission_details / SapWindow.frame_factor
still take precedence. Overshading factor stays at 0.77 ("average") since
RdSAP 10 doesn't lodge a per-window overshading code.

100-cert parity probe:
  MAE 5.65 → 5.70  (flat)
  exact-match within ±1: 18% → 20%
  bias +1.13 → +1.50

Slight bias drift toward over-prediction is expected — bigger solar
gains reduce predicted heating demand. Net: the engine is now more
spec-correct (more exact matches), but composition of errors elsewhere
needs the next slice to bring bias back toward 0.

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

packages/domain/src/domain/sap/rdsap/cert_to_inputs.py

@@ -88,6 +88,41 @@ _ORIENTATION_BY_CODE: Final[dict[int, Orientation]] = {
 }
 
 
+# SAP 10.3 Table 6b — g_perpendicular (solar transmittance at normal
+# incidence) by SAP10 glazing_type code. Default 0.72 (modern double
+# glazing, no low-E) when the cert's glazing_type is missing or
+# unrecognised — the modal RdSAP case.
+_G_PERPENDICULAR_BY_GLAZING_TYPE: Final[dict[int, float]] = {
+    1: 0.85,  # single
+    2: 0.72,  # double 2002-2022 (no low-E)
+    3: 0.72,  # double pre-2002
+    4: 0.63,  # double low-E soft coat
+    5: 0.76,  # secondary glazing
+    6: 0.68,  # triple
+}
+_G_PERPENDICULAR_DEFAULT: Final[float] = 0.72
+
+
+# SAP 10.3 Table 6c — frame factor (proportion of window area that is
+# glazed, not frame) by frame material. The cert lodges this as a free-
+# text string ("PVC", "Wood", "Metal", "Aluminium"); matching is case-
+# insensitive and substring-based because site-notes capitalisation
+# drifts.
+_FRAME_FACTOR_BY_MATERIAL: Final[tuple[tuple[str, float], ...]] = (
+    ("metal with thermal break", 0.80),
+    ("metal", 0.83),
+    ("aluminium with thermal break", 0.80),
+    ("aluminium", 0.83),
+    ("steel", 0.83),
+    ("wood", 0.70),
+    ("timber", 0.70),
+    ("pvc", 0.70),
+    ("upvc", 0.70),
+    ("composite", 0.70),
+)
+_FRAME_FACTOR_DEFAULT: Final[float] = 0.70
+
+
 # SAP 10.3 Table 12 CO2 emission factors (kg CO2 / kWh delivered).
 # Keys are SAP 10.2 Table 32 fuel codes (the existing fuel-price keys);
 # anything not listed cascades to mains-gas baseline.
@@ -206,14 +241,39 @@ def _living_area_fraction(habitable_rooms_count: Optional[int]) -> float:
     return _LIVING_AREA_FRACTION_MIN
 
 
+def _g_perpendicular(w: SapWindow) -> float:
+    """Solar transmittance at normal incidence per SAP 10.3 Table 6b.
+    Prefer the cert's measured value (`window_transmission_details`);
+    otherwise look up by `glazing_type`."""
+    if w.window_transmission_details is not None:
+        return float(w.window_transmission_details.solar_transmittance)
+    if isinstance(w.glazing_type, int) and w.glazing_type in _G_PERPENDICULAR_BY_GLAZING_TYPE:
+        return _G_PERPENDICULAR_BY_GLAZING_TYPE[w.glazing_type]
+    return _G_PERPENDICULAR_DEFAULT
+
+
+def _frame_factor(w: SapWindow) -> float:
+    """SAP 10.3 Table 6c frame factor. Prefer the cert's measured value
+    (`SapWindow.frame_factor`); otherwise look up by `frame_material`."""
+    if w.frame_factor is not None:
+        return float(w.frame_factor)
+    material = (w.frame_material or "").lower()
+    for needle, ff in _FRAME_FACTOR_BY_MATERIAL:
+        if needle in material:
+            return ff
+    return _FRAME_FACTOR_DEFAULT
+
+
 def _window_inputs(windows: list[SapWindow]) -> tuple[WindowInput, ...]:
     """Map each cert window with a known SAP octant to a `WindowInput`.
 
-    Defaults for the optical / shading factors are SAP 10.3 Table 6b/6c/6d
-    typicals (low-e double-glazing, PVC frame, average overshading) — the
-    cert rarely carries these directly. Pitch = 90° (vertical windows).
-    Windows whose orientation isn't in 1-8 are dropped, matching the live
-    ML feature-builder convention.
+    `g_perpendicular` follows SAP 10.3 Table 6b (by glazing_type when no
+    measured transmission details), `frame_factor` follows Table 6c (by
+    frame_material when no measured value). Overshading factor stays at
+    SAP's "average" default 0.77 because the cert doesn't lodge a per-
+    window overshading code in RdSAP 10. Pitch = 90° (vertical windows).
+    Windows whose orientation isn't in 1-8 are dropped, matching the
+    live ML feature-builder convention.
     """
     out: list[WindowInput] = []
     for w in windows:
@@ -221,19 +281,13 @@ def _window_inputs(windows: list[SapWindow]) -> tuple[WindowInput, ...]:
         if orientation_code is None or orientation_code not in _ORIENTATION_BY_CODE:
             continue
         area = float(w.window_width) * float(w.window_height)
-        g = (
-            float(w.window_transmission_details.solar_transmittance)
-            if w.window_transmission_details is not None
-            else 0.63
-        )
-        ff = float(w.frame_factor) if w.frame_factor is not None else 0.7
         out.append(
             WindowInput(
                 area_m2=area,
                 orientation=_ORIENTATION_BY_CODE[orientation_code],
                 pitch_deg=90.0,
-                g_perpendicular=g,
-                frame_factor=ff,
+                g_perpendicular=_g_perpendicular(w),
+                frame_factor=_frame_factor(w),
                 overshading_factor=0.77,
             )
         )

packages/domain/src/domain/sap/rdsap/tests/test_cert_to_inputs.py

@@ -253,6 +253,42 @@ def test_main_heating_control_code_maps_to_sap_control_type() -> None:
     assert type_3.control_type == 3
 
 
+def test_window_g_perpendicular_uses_table_6b_by_glazing_type() -> None:
+    # Arrange — SAP 10.3 Table 6b: g⊥ depends on the glazing type when
+    # transmission details aren't measured. Single (code 1) → 0.85;
+    # double low-E soft coat (code 4) → 0.63; triple (code 6) → 0.68.
+    single = make_window(orientation=5, glazing_type=1, frame_material="PVC")
+    triple = make_window(orientation=5, glazing_type=6, frame_material="PVC")
+    low_e_double = make_window(orientation=5, glazing_type=4, frame_material="PVC")
+    base = _typical_semi_detached_epc()
+    base.sap_windows = [single, triple, low_e_double]
+
+    # Act
+    inputs = cert_to_inputs(base)
+
+    # Assert — same orientation, three different glazing types.
+    g_values = sorted(w.g_perpendicular for w in inputs.windows)
+    assert g_values == [0.63, 0.68, 0.85]
+
+
+def test_window_frame_factor_uses_table_6c_by_frame_material() -> None:
+    # Arrange — Table 6c: PVC/Wood = 0.70; aluminium / steel = 0.83
+    # (no thermal break). Metal-with-thermal-break would be 0.80 but
+    # not tested here since cert strings rarely carry that distinction.
+    pvc = make_window(orientation=5, frame_material="PVC")
+    wood = make_window(orientation=5, frame_material="Wood")
+    aluminium = make_window(orientation=5, frame_material="Aluminium")
+    base = _typical_semi_detached_epc()
+    base.sap_windows = [pvc, wood, aluminium]
+
+    # Act
+    inputs = cert_to_inputs(base)
+
+    # Assert
+    ff_values = sorted(w.frame_factor for w in inputs.windows)
+    assert ff_values == [0.70, 0.70, 0.83]
+
+
 def test_electric_storage_heater_space_heating_at_off_peak_rate() -> None:
     # Arrange — RdSAP convention: when the main heating is electric-
     # storage (code 401-409) or direct-electric (191-196), space heating