Slice 40: room_in_roof_type_1 gable lengths flow through schema-21 to EpcPropertyData

Schema-21.0.0/0.1's SapRoomInRoof dataclass declared only floor_area
and construction_age_band. Real certs lodge gable wall lengths under
sap_room_in_roof.room_in_roof_type_1 (RdSAP §3.9.1 Simplified Type 1).
from_dict silently dropped the whole block at deserialization, so the
mapper never had a chance to surface the lengths on EpcPropertyData.

Fix: add RoomInRoofType1 dataclass to both schema-21 variants;
extend SapRoomInRoof with `room_in_roof_type_1: Optional[...]`;
update the mapper to populate EpcPropertyData.SapRoomInRoof
gable_1_length_m / gable_2_length_m from the new field.

Calculator behaviour unchanged this slice: heat_transmission.py:243
requires BOTH length AND height to contribute gable area, and the
cert lodges length only (RdSAP §3.9.1 uses a default 2.45 m storey
height — not yet plumbed). Cert 0240's −12 SAP residual unchanged.

Schema scope: both 21.0.0 and 21.0.1 schemas (identical SapBuildingPart
mapper code, kept consistent). Older schemas (17/18/19/20) don't carry
this RR shape on their dataclasses and are out of scope per the prior
cohort scope decision.

Unblocks the follow-up slices that close the RR cascade: default
H_gable in calculator or mapper, parse "Roof room(s), insulated
(assumed)" description for the U-value override, etc.

930/930 Elmhurst cascade green. 14/14 golden cohort green at pinned
residuals (no shift, as expected). 76/76 mapper tests green.
Pyright net-zero (32 errors before and after).

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

datatypes/epc/domain/mapper.py

@@ -1233,6 +1233,19 @@ class EpcPropertyDataMapper:
                         SapRoomInRoof(
                             floor_area=_measurement_value(bp.sap_room_in_roof.floor_area),
                             construction_age_band=bp.sap_room_in_roof.construction_age_band,
+                            # RdSAP §3.9.1 Simplified Type 1: gable lengths
+                            # only (no heights — the cascade applies the
+                            # 2.45 m default storey height per §3.9.1).
+                            gable_1_length_m=(
+                                bp.sap_room_in_roof.room_in_roof_type_1.gable_wall_length_1
+                                if bp.sap_room_in_roof.room_in_roof_type_1 is not None
+                                else None
+                            ),
+                            gable_2_length_m=(
+                                bp.sap_room_in_roof.room_in_roof_type_1.gable_wall_length_2
+                                if bp.sap_room_in_roof.room_in_roof_type_1 is not None
+                                else None
+                            ),
                         )
                         if bp.sap_room_in_roof
                         else None
@@ -1478,6 +1491,19 @@ class EpcPropertyDataMapper:
                         SapRoomInRoof(
                             floor_area=_measurement_value(bp.sap_room_in_roof.floor_area),
                             construction_age_band=bp.sap_room_in_roof.construction_age_band,
+                            # RdSAP §3.9.1 Simplified Type 1: gable lengths
+                            # only (no heights — the cascade applies the
+                            # 2.45 m default storey height per §3.9.1).
+                            gable_1_length_m=(
+                                bp.sap_room_in_roof.room_in_roof_type_1.gable_wall_length_1
+                                if bp.sap_room_in_roof.room_in_roof_type_1 is not None
+                                else None
+                            ),
+                            gable_2_length_m=(
+                                bp.sap_room_in_roof.room_in_roof_type_1.gable_wall_length_2
+                                if bp.sap_room_in_roof.room_in_roof_type_1 is not None
+                                else None
+                            ),
                         )
                         if bp.sap_room_in_roof
                         else None

datatypes/epc/domain/tests/test_from_rdsap_schema.py

@@ -587,6 +587,25 @@ class TestFromRdSapSchema21_0_1:
     def test_party_wall_length(self, result: EpcPropertyData) -> None:
         assert result.sap_building_parts[0].sap_floor_dimensions[0].party_wall_length_m == 7.9
 
+    # --- room-in-roof (sap_room_in_roof.room_in_roof_type_1) ---
+
+    def test_sap_room_in_roof_gable_lengths_extracted_from_room_in_roof_type_1(
+        self, result: EpcPropertyData
+    ) -> None:
+        # Arrange — schema-21.0.1 lodges Simplified Type 1 gable lengths
+        # under sap_room_in_roof.room_in_roof_type_1. The cascade requires
+        # them on EpcPropertyData.SapRoomInRoof.gable_1_length_m /
+        # gable_2_length_m for the §3.9.2 area cascade. Without this the
+        # length data is silently dropped at deserialization.
+
+        # Act
+        rir = result.sap_building_parts[0].sap_room_in_roof
+
+        # Assert
+        assert rir is not None
+        assert rir.gable_1_length_m == 6.4
+        assert rir.gable_2_length_m == 6.4
+
     # --- ventilation (sap_ventilation) ---
 
     def test_sap_ventilation_extract_fans_count_flows_through_to_calculator_input(

datatypes/epc/schema/rdsap_schema_21_0_0.py

@@ -166,11 +166,26 @@ class SapFloorDimension:
     floor_construction: Optional[int] = None
 
 
+@dataclass
+class RoomInRoofType1:
+    """RdSAP §3.9.1 Simplified Type 1 RR — gable lengths only.
+
+    `gable_wall_type_*` is the Table 4 gable variant (0 = external, etc.;
+    full enum not yet mapped). `gable_wall_length_*` is the run of the
+    external gable in metres. Heights are NOT lodged here — the cascade
+    applies the §3.9.1 default storey height (2.45 m)."""
+    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
+
+
 @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
 
 
 @dataclass

datatypes/epc/schema/rdsap_schema_21_0_1.py

@@ -176,10 +176,25 @@ class SapFloorDimension:
     floor_construction: Optional[int] = None
 
 
+@dataclass
+class RoomInRoofType1:
+    """RdSAP §3.9.1 Simplified Type 1 RR — gable lengths only.
+
+    `gable_wall_type_*` is the Table 4 gable variant (0 = external, etc.;
+    full enum not yet mapped). `gable_wall_length_*` is the run of the
+    external gable in metres. Heights are NOT lodged here — the cascade
+    applies the §3.9.1 default storey height (2.45 m)."""
+    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
+
+
 @dataclass
 class SapRoomInRoof:
     floor_area: Union[int, float]
     construction_age_band: str
+    room_in_roof_type_1: Optional[RoomInRoofType1] = None
 
 
 @dataclass

datatypes/epc/schema/tests/fixtures/21_0_1.json

@@ -126,7 +126,16 @@
       "identifier": "Main Dwelling",
       "wall_dry_lined": "N",
       "floor_heat_loss": 7,
-      "sap_room_in_roof": {"floor_area": 100, "construction_age_band": "B"},
+      "sap_room_in_roof": {
+        "floor_area": 100,
+        "construction_age_band": "B",
+        "room_in_roof_type_1": {
+          "gable_wall_type_1": 0,
+          "gable_wall_type_2": 0,
+          "gable_wall_length_1": 6.4,
+          "gable_wall_length_2": 6.4
+        }
+      },
       "roof_construction": 4,
       "wall_construction": 4,
       "building_part_number": 1,