Slice 99b: Elmhurst mapper — flat floor-position from floor.location

For flats, `EpcPropertyData.dwelling_type` needs a "Top-floor" /
"Mid-floor" / "Ground-floor" prefix so the cascade's
`_dwelling_exposure` (cert_to_inputs.py) gates floor + roof party-
surface routing correctly per RdSAP 10 §5. Before Slice 99a, the
broken `built_form` ("2.0 Number of Storeys:") meant cert 9501's
`dwelling_type` was "2.0 Number of Storeys: flat" — never matched
any flat-prefix in the cascade, so the cert was treated as a fully-
exposed dwelling (worksheet had floor U=0 / party-ceiling-down, but
cascade routed both as exposed → Δ +9.25 W/K on floor alone). After
99a's empty-attachment fix the prefix was just " flat" — still no
match.

Slice 99b composes the position prefix from the Summary's lodged
floor location + RR presence:
- floor.location lodges "dwelling below" → floor is party
  - + RR present → Top-floor (roof exposed)
  - + no RR → Mid-floor (roof party)
- floor.location doesn't lodge dwelling below → Ground-floor

For cert 9501: floor.location="A Another dwelling below" + RR
present (cert lodges Room-in-Roof with gable walls + flat ceiling).
Resulting `dwelling_type` = "Top-floor flat" — matches the cascade's
`_dwelling_exposure` "top-floor" prefix → has_exposed_floor=False,
has_exposed_roof=True, the worksheet's exposure shape.

Houses keep the historical contract: `f"{built_form}
{property_type.lower()}"` — cohort hand-builts and the 2 boiler
chain tests (001479 + 0330) unchanged.

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

backend/documents_parser/tests/test_summary_pdf_mapper_chain.py

@@ -321,6 +321,33 @@ def test_summary_9501_flat_has_no_built_form_in_summary_pdf() -> None:
     assert epc.built_form == ""
 
 
+def test_summary_9501_dwelling_type_is_top_floor_flat() -> None:
+    # Arrange — cert 9501's worksheet treats the cert as a TOP-floor
+    # flat: §3 (28a) "Ground floor Main … U=0.0" because the floor
+    # sits over "Another dwelling below" (worksheet line 9.0 Floor
+    # location); §3 (30) has both an external roof + RR contributions
+    # so the roof IS exposed. The cascade's `_dwelling_exposure`
+    # function does prefix matching on `dwelling_type.lower()` to gate
+    # which surfaces are party — without "top-floor flat" the cert
+    # falls through to fully-exposed houses (Δ +9.25 W/K on floor).
+    #
+    # Floor-position inference rules:
+    # - floor.location indicates "Another dwelling below"
+    #   → not ground floor (rules out ground-floor flat)
+    # - room_in_roof OR external roof present
+    #   → roof exposed (rules out mid-floor flat)
+    # - therefore → top-floor flat
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_000784_PDF)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+
+    # Act
+    epc = EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)
+
+    # Assert
+    assert epc.dwelling_type is not None
+    assert epc.dwelling_type.lower().startswith("top-floor")
+
+
 def test_summary_001479_full_chain_sap_matches_worksheet_pdf_exactly() -> None:
     # Arrange — cert 001479 (Summary_001479.pdf / P960-0001-001479.pdf)
     # is the first cohort cert with a real GOV.UK EPB API counterpart

datatypes/epc/domain/mapper.py

@@ -271,8 +271,15 @@ class EpcPropertyDataMapper:
         prefix = pd.house_number or pd.house_name or ""
         address_line_1 = f"{prefix}, {pd.street}" if prefix else pd.street
 
+        dwelling_type = _elmhurst_dwelling_type(
+            built_form=built_form,
+            property_type=property_type,
+            floor=survey.floor,
+            room_in_roof=survey.room_in_roof,
+        )
+
         return EpcPropertyData(
-            dwelling_type=f"{built_form} {property_type.lower()}",
+            dwelling_type=dwelling_type,
             inspection_date=pd.inspection_date,
             tenure=pd.tenure,
             transaction_type=pd.transaction_type,
@@ -2080,6 +2087,44 @@ _ELMHURST_INSULATION_CODE_TO_SAP10: Dict[str, int] = {
 }
 
 
+def _elmhurst_dwelling_type(
+    *,
+    built_form: str,
+    property_type: str,
+    floor: Optional[ElmhurstFloorDetails],
+    room_in_roof: Optional[ElmhurstRoomInRoof],
+) -> str:
+    """Compose `EpcPropertyData.dwelling_type` from the Elmhurst Summary's
+    property-type + attachment + floor-location + RR presence.
+
+    For HOUSES: returns `f"{built_form} {property_type.lower()}"` — the
+    historical contract ("Mid-Terrace house", "Detached house").
+
+    For FLATS: derives the floor-position prefix ("Top-floor",
+    "Mid-floor", "Ground-floor") from `floor.location` + RR presence:
+    - floor lodges "dwelling below" → roof exposed (RR present or
+      external roof) → Top-floor; roof party (no RR/external) →
+      Mid-floor;
+    - floor not over another dwelling → Ground-floor.
+
+    The cascade's `_dwelling_exposure` (cert_to_inputs.py) is prefix-
+    matched on the lowercase result; correct flat-prefix detection is
+    the gate for floor / roof party-surface routing (RdSAP 10 §5).
+    """
+    if property_type.lower() != "flat":
+        return f"{built_form} {property_type.lower()}".strip()
+    floor_loc = (floor.location if floor is not None else "") or ""
+    has_dwelling_below = "dwelling below" in floor_loc.lower()
+    has_exposed_roof = room_in_roof is not None
+    if has_dwelling_below and has_exposed_roof:
+        position = "Top-floor"
+    elif has_dwelling_below:
+        position = "Mid-floor"
+    else:
+        position = "Ground-floor"
+    return f"{position} flat"
+
+
 def _elmhurst_wall_construction_int(coded: str) -> Optional[int]:
     """Map an Elmhurst wall_type string ('CA Cavity') to the SAP10
     integer code (4). Returns None when the leading code isn't a known