diff --git a/datatypes/epc/domain/epc_property_data.py b/datatypes/epc/domain/epc_property_data.py
index 328397e82..d55aa1593 100644
--- a/datatypes/epc/domain/epc_property_data.py
+++ b/datatypes/epc/domain/epc_property_data.py
@@ -39,12 +39,13 @@ class BuildingPartIdentifier(Enum):
         cls, api_identifier: Optional[object]
     ) -> "BuildingPartIdentifier":
         """Map a gov-EPC API `BuildingPart.identifier` to its canonical
-        member. "Main Dwelling" → MAIN; "Extension N" → EXTENSION_N
+        member. "Main Dwelling" / "Main building" (the 2011-era LIG-lodged
+        SAP-Schema-15.0 wording) → MAIN; "Extension N" → EXTENSION_N
         (for N in 1..4). `None` (permitted by the 21_0_1 schema), a non-string
         identifier (some SAP-16.x certs lodge a bare int), and anything else
         unrecognised fall to OTHER.
         """
-        if api_identifier == "Main Dwelling":
+        if api_identifier in ("Main Dwelling", "Main building"):
             return cls.MAIN
         if isinstance(api_identifier, str):
             match = _API_EXTENSION.match(api_identifier)
diff --git a/tests/datatypes/epc/domain/test_building_part_identifier.py b/tests/datatypes/epc/domain/test_building_part_identifier.py
index d792f45a0..e3a725694 100644
--- a/tests/datatypes/epc/domain/test_building_part_identifier.py
+++ b/tests/datatypes/epc/domain/test_building_part_identifier.py
@@ -9,6 +9,17 @@ def test_main_dwelling_maps_to_main() -> None:
     )
 
 
+def test_main_building_maps_to_main() -> None:
+    # SAP-Schema-15.0 (2011-era LIG-lodged) certs use "Main building" instead
+    # of "Main Dwelling" for the main dwelling's building-part identifier.
+    # Previously this fell to OTHER, leaving the property with no MAIN part
+    # and crashing every recommendation generator that assumes one exists
+    # (e.g. `next(...)` with no default in wall_recommendation.py).
+    assert BuildingPartIdentifier.from_api_string("Main building") == (
+        BuildingPartIdentifier.MAIN
+    )
+
+
 def test_extension_string_maps_to_numbered_extension() -> None:
     assert BuildingPartIdentifier.from_api_string("Extension 2") == (
         BuildingPartIdentifier.EXTENSION_2