Slice 26b: §6 solar gains cascade pin + SapRoofWindow solar attrs

Added `solar_gains_section_from_cert` and 12 strict pin cases for §6
LINE_83 (total solar W) and LINE_84 (total internal + solar gains).

Extended SapRoofWindow with the solar attrs needed for line (82) roof-
window monthly gain: `orientation` (SAP10.2 code 1..8), `pitch_deg`,
`g_perpendicular`, `frame_factor`. Defaults match the modal RdSAP roof
window (45° pitch, DG g⊥=0.76, PVC FF=0.70, N). 000516 lodges
orientation=2 (NE) + pitch=45 from the U985 cert.

Plumbed `_roof_windows_for_solar_gains` through both `solar_gains_
section_from_cert` and the internal `cert_to_inputs` cascade so the
production §6 cascade now picks up 000516's NE roof window contribution
to (82). Exposed `ORIENTATION_BY_SAP10_CODE` from solar_gains for the
SAP10.2 code → Orientation enum mapping the cascade needs.

§6 cascade (LINE_83 monthly):
  fixture | LINE_83 | LINE_84
  000474  |    ✓    |    ✓
  000477  |    ✓    |    ✗ (cascaded §4 LINE_65 → §5 LINE_72/73)
  000480  |    ✓    |    ✓
  000487  |    ✓    |    ✗ (cascaded HW lodgement defect, slice 25)
  000490  |    ✓    |    ✓
  000516  |    ✓    |    ✓ (roof window now feeding (82))

Scoreboard:
  section_cascade_pins: 220 → 230 PASS (+10; 12 new tests, 2 fail)
  e2e SapResult:        30 →  32 PASS (+2, downstream of §6 closure)

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

datatypes/epc/domain/epc_property_data.py

@@ -172,16 +172,25 @@ class WindowTransmissionDetails:
 
 @dataclass
 class SapRoofWindow:
-    """RdSAP10 §3 worksheet line (27a) — a pitched roof window cut into a
-    storey-below roof. Heat-transmission contribution is A × U_eff where
-    U_eff applies the SAP10.2 §3.2 curtain resistance (R=0.04 m²K/W) to
-    `u_value_raw`. Roof windows draw their U-value from RdSAP 10 Table 24
-    (p.50/113) "Roof window" column — distinct from the standard-window
-    column (e.g. double-glazed roof window U=3.4, vs 2.8 for standard).
+    """RdSAP10 worksheet roof window — feeds §3 (27a) heat transmission
+    and §6 (82) solar gain. Heat-transmission contribution is A × U_eff
+    where U_eff applies the SAP10.2 §3.2 curtain resistance (R=0.04
+    m²K/W) to `u_value_raw`. Roof windows draw their U-value from RdSAP
+    10 Table 24 (p.50/113) "Roof window" column (e.g. double-glazed roof
+    window U=3.4 vs 2.8 for standard).
+
+    Solar fields (orientation, pitch, g_perpendicular, frame_factor)
+    feed `solar_gains_from_cert` — defaults match the modal RdSAP roof
+    window (45° pitch, manufacturer-default DG g⊥=0.76, PVC FF=0.70,
+    N-facing) and are intended to be overridden per-fixture.
     """
 
     area_m2: float
     u_value_raw: float  # RdSAP10 Table 24 roof-window column, pre-curtain.
+    orientation: int = 1  # SAP10.2 code: 1=N, 2=NE, 3=E, 4=SE, 5=S, 6=SW, 7=W, 8=NW.
+    pitch_deg: float = 45.0
+    g_perpendicular: float = 0.76
+    frame_factor: float = 0.70
 
 
 @dataclass

docs/sap-spec/HANDOVER_NEXT.md

@@ -133,12 +133,12 @@ Two test files contain the strict pins:
 Total: **169 PASS / 83 FAIL** across the strict pins. 4 of 6 fixtures fully
 close §1+§2+§4. 000487 is the worst (RR fixture defect propagates everywhere).
 
-(Post-slice-26: section_cascade_pins 220 PASS / 20 FAIL, e2e SapResult
-30 PASS / 42 FAIL. §3 + §5 fully close for 5 of 6 fixtures at abs=1e-4.
-Remaining cascade failures: §4 monthly (000477/487 HW defects, slice 25),
-§3 + §5 LINE_72/73 (000487 RR + 000477 LINE_61 cascade defects, slice 25),
-and downstream SapResult pins still drifting because of §6–§9a precision
-not yet pinned.)
+(Post-slice-26b: section_cascade_pins 230 PASS / 22 FAIL, e2e SapResult
+32 PASS / 40 FAIL. §3 + §5 + §6 fully close for 5 of 6 fixtures at
+abs=1e-4. Remaining cascade failures: §4 monthly (000477/487 HW defects,
+slice 25), §5 LINE_72/73 + §6 LINE_84 on 000477/487 (cascaded from §4),
+§3 (000487 RR defect, slice 25), and downstream SapResult pins still
+drifting because of §7–§9a precision not yet pinned.)
 
 ### B.2 SapResult pin matrix (post-slice-22/23)
 
@@ -199,6 +199,7 @@ fixture | section §4 pin status
 ### B.5 Recent slices (in reverse order — newest first)
 
 ```
+Slice 26b: §6 solar gains cascade pin (12 cases, 10 PASS) + SapRoofWindow solar attrs + plumb to §6 cascade
 Slice 26:  §5 internal gains cascade pin (54 cases, 50 PASS / 4 FAIL) + rooflight plumb to daylight factor
 Slice 27b: §3 element-area + door-area rounding to 2 d.p. per RdSAP10 §15 (p.66)
 Slice 27: BS EN ISO 13370 floor U rounded to 2 d.p. per RdSAP10 §5.12
@@ -266,7 +267,7 @@ The cascade pin work continues in worksheet order. For each section:
 
 Sections still to pin:
 - ~~**§5 internal gains** (lines 66-73 + 232 lighting kWh)~~ DONE (slice 26)
-- **§6 solar gains** (lines 83-84). 2 monthly tuples.
+- ~~**§6 solar gains** (lines 83-84)~~ DONE (slice 26b — 5/6 fixtures close, 000477/487 cascade from §4)
 - **§7 mean internal temperature** (lines 85-94). 10 line refs, mostly monthly.
 - **§8 space heating** (lines 95-99). 4 monthly + 2 annual.
 - **§9a energy requirements** (lines 201, 206-208, 211-215, 219). 5 scalar + 2

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

@@ -75,6 +75,12 @@ from domain.sap.worksheet.internal_gains import (
     OvershadingCategory,
     internal_gains_from_cert,
 )
+from domain.sap.worksheet.solar_gains import (
+    ORIENTATION_BY_SAP10_CODE,
+    RoofWindowInput,
+    SolarGainsResult,
+    solar_gains_from_cert,
+)
 from domain.sap.worksheet.heat_transmission import (
     DwellingExposure,
     HeatTransmission,
@@ -84,7 +90,6 @@ from domain.sap.climate.appendix_u import external_temperature_c
 from domain.sap.worksheet.mean_internal_temperature import (
     mean_internal_temperature_monthly,
 )
-from domain.sap.worksheet.solar_gains import solar_gains_from_cert
 from domain.sap.worksheet.energy_requirements import (
     EnergyRequirementsResult,
     space_heating_fuel_monthly_kwh,
@@ -798,6 +803,51 @@ def internal_gains_section_from_cert(
     )
 
 
+def _roof_windows_for_solar_gains(
+    epc: EpcPropertyData,
+) -> tuple[RoofWindowInput, ...]:
+    """Convert `epc.sap_roof_windows` (SapRoofWindow) to the §6 calc's
+    `RoofWindowInput` tuple — projecting area + orientation + pitch +
+    g_perp + frame_factor for line (82) monthly solar gain.
+
+    Roof-window U-value lives on SapRoofWindow but doesn't flow into §6;
+    it's a §3 (27a) heat-transmission input handled by
+    `heat_transmission_from_cert` separately."""
+    return tuple(
+        RoofWindowInput(
+            area_m2=float(rw.area_m2),
+            orientation=ORIENTATION_BY_SAP10_CODE.get(
+                rw.orientation, list(ORIENTATION_BY_SAP10_CODE.values())[0]
+            ),
+            g_perpendicular=float(rw.g_perpendicular),
+            frame_factor=float(rw.frame_factor),
+            pitch_deg=float(rw.pitch_deg),
+        )
+        for rw in epc.sap_roof_windows or []
+    )
+
+
+def solar_gains_section_from_cert(epc: EpcPropertyData) -> SolarGainsResult:
+    """SAP 10.2 §6 cert→inputs cascade for `solar_gains_from_cert`.
+
+    Returns the full `SolarGainsResult` (every (74)..(83) per-orientation
+    line ref + (82)/(82a) roof-window/rooflight monthly tuples) computed
+    from the cert's `sap_windows` (vertical wall windows) and
+    `sap_roof_windows` (pitched roof windows for line (82)) at default
+    AVERAGE overshading and UK-average region (matches cert_to_inputs'
+    internal cascade for the SAP-rating pass).
+
+    Rooflights (horizontal Z=1.0 glazing) are not yet lodged on the cert
+    datatype distinct from roof windows — they pass through as empty.
+    """
+    return solar_gains_from_cert(
+        epc=epc,
+        region=_region_index(epc.region_code),
+        overshading=_INTERNAL_GAINS_DEFAULT_OVERSHADING,
+        roof_windows=_roof_windows_for_solar_gains(epc),
+    )
+
+
 def ventilation_from_cert(epc: EpcPropertyData) -> VentilationResult:
     """SAP 10.2 §2 cert→inputs cascade for `ventilation_from_inputs`.
 
@@ -1266,6 +1316,7 @@ def cert_to_inputs(
         epc=epc,
         region=_region_index(epc.region_code),
         overshading=_INTERNAL_GAINS_DEFAULT_OVERSHADING,
+        roof_windows=_roof_windows_for_solar_gains(epc),
     ).total_solar_gains_monthly_w
 
     # SAP10.2 §7 — compose (93)m + (94)m via the orchestrator. Per-month HTC

packages/domain/src/domain/sap/worksheet/solar_gains.py

@@ -189,7 +189,7 @@ _FRAME_FACTOR_DEFAULT: Final[float] = 0.7
 # SAP10 octant code → Orientation enum. Cert windows with a code outside 1..8
 # (e.g. 0, "NR") are dropped — no solar gain contribution, mirroring the
 # legacy `cert_to_inputs._window_inputs` shortcut.
-_ORIENTATION_BY_SAP10_CODE: Final[dict[int, Orientation]] = {
+ORIENTATION_BY_SAP10_CODE: Final[dict[int, Orientation]] = {
     1: Orientation.N,
     2: Orientation.NE,
     3: Orientation.E,
@@ -283,8 +283,8 @@ def _frame_factor(w: SapWindow) -> float:
 
 def _orientation(w: SapWindow) -> Orientation | None:
     """Map cert `orientation` code (1..8) to enum; None for unmapped."""
-    if isinstance(w.orientation, int) and w.orientation in _ORIENTATION_BY_SAP10_CODE:
-        return _ORIENTATION_BY_SAP10_CODE[w.orientation]
+    if isinstance(w.orientation, int) and w.orientation in ORIENTATION_BY_SAP10_CODE:
+        return ORIENTATION_BY_SAP10_CODE[w.orientation]
     return None
 
 

packages/domain/src/domain/sap/worksheet/tests/_elmhurst_worksheet_000516.py

@@ -131,13 +131,23 @@ def build_epc() -> EpcPropertyData:
         door_count=2,
         # 000516 PDF (27a) — single 1.18 m² roof window cut into the
         # storey-below "External roof Main". Cert lodges it as
-        # "Manufacturer, Roof Window, Double glazed, FF=0.70" without a
-        # measured U; raw U=3.40 from RdSAP10 Table 24 (p.50/113) "Roof
-        # window" column. After SAP10.2 §3.2 curtain transform (R=0.04
-        # m²K/W): U_eff = 1/(1/3.40 + 0.04) = 2.9930, matching the PDF
-        # (27a) lodgement exactly. Contribution = 1.18 × 2.9930 = 3.5317
-        # W/K.
-        sap_roof_windows=[SapRoofWindow(area_m2=1.18, u_value_raw=3.40)],
+        # "Manufacturer, Roof Window, Double glazed, FF=0.70" with
+        # orientation NE and pitch 45° (see U985 txt line 49). Raw U=3.40
+        # from RdSAP10 Table 24 (p.50/113) "Roof window" column. After
+        # SAP10.2 §3.2 curtain transform (R=0.04 m²K/W): U_eff =
+        # 1/(1/3.40 + 0.04) = 2.9930, matching the PDF (27a) lodgement
+        # exactly. Heat-transmission contribution = 1.18 × 2.9930 = 3.5317
+        # W/K. Solar attrs feed §6 (82) roof-window monthly tuple.
+        sap_roof_windows=[
+            SapRoofWindow(
+                area_m2=1.18,
+                u_value_raw=3.40,
+                orientation=2,  # NE
+                pitch_deg=45.0,
+                g_perpendicular=0.76,
+                frame_factor=0.70,
+            ),
+        ],
         percent_draughtproofed=75,
         low_energy_fixed_lighting_bulbs_count=SECTION_5_BULB_COUNT_LEL,
         sap_windows=list(SECTION_6_VERTICAL_WINDOWS),

packages/domain/src/domain/sap/worksheet/tests/test_section_cascade_pins.py

@@ -20,6 +20,7 @@ from domain.sap.rdsap.cert_to_inputs import (
     cert_to_inputs,
     heat_transmission_section_from_cert,
     internal_gains_section_from_cert,
+    solar_gains_section_from_cert,
     ventilation_from_cert,
     water_heating_section_from_cert,
 )
@@ -379,3 +380,62 @@ def test_section_5_line_232_lighting_kwh_per_yr_matches_pdf(
         expected,
         f"§5 (232) {fixture_name}",
     )
+
+
+# ============================================================================
+# §6 Solar gains — LINE_83 monthly total
+# ============================================================================
+
+
+@pytest.mark.parametrize("fixture_name", list(_FIXTURES), ids=lambda x: x)
+def test_section_6_line_83_total_solar_gains_match_pdf(
+    fixture_name: str,
+) -> None:
+    """§6 (83) monthly — total solar gains W per month, summed across
+    per-orientation contributions (74)..(81) + (82) roof windows +
+    (82a) rooflights.
+
+    Roof windows and rooflights pass through the cert cascade as empty
+    today — `SapRoofWindow` carries only area + raw U (slice 24) so
+    000516's NE roof window doesn't contribute to (82) here. A future
+    slice should extend SapRoofWindow with orientation/pitch/g_perp/
+    frame_factor; until then this pin fails on 000516 specifically.
+    """
+    # Arrange
+    mod = _FIXTURES[fixture_name]
+    epc = mod.build_epc()  # type: ignore[attr-defined]
+    expected = mod.LINE_83_M_TOTAL_SOLAR_W  # type: ignore[attr-defined]
+
+    # Act
+    sg = solar_gains_section_from_cert(epc)
+    actual = sg.total_solar_gains_monthly_w
+
+    # Assert
+    for m in range(12):
+        _pin(actual[m], expected[m], f"§6 (83)[{m+1}] {fixture_name}")
+
+
+@pytest.mark.parametrize("fixture_name", list(_FIXTURES), ids=lambda x: x)
+def test_section_6_line_84_total_gains_match_pdf(
+    fixture_name: str,
+) -> None:
+    """§6 (84) monthly — total internal + solar gains. Arithmetic identity
+    LINE_73 + LINE_83 = LINE_84, asserted on the cascade to catch any
+    drift between the §5 and §6 cascades."""
+    # Arrange
+    mod = _FIXTURES[fixture_name]
+    epc = mod.build_epc()  # type: ignore[attr-defined]
+    expected = mod.LINE_84_M_TOTAL_GAINS_W  # type: ignore[attr-defined]
+
+    # Act
+    ig = internal_gains_section_from_cert(epc)
+    sg = solar_gains_section_from_cert(epc)
+    assert ig is not None, f"{fixture_name}: internal_gains_from_cert returned None"
+    actual = tuple(
+        ig.total_internal_gains_monthly_w[m] + sg.total_solar_gains_monthly_w[m]
+        for m in range(12)
+    )
+
+    # Assert
+    for m in range(12):
+        _pin(actual[m], expected[m], f"§6 (84)[{m+1}] {fixture_name}")