diff --git a/backend/documents_parser/tests/test_summary_pdf_mapper_chain.py b/backend/documents_parser/tests/test_summary_pdf_mapper_chain.py
index fa79dabe..a9ad62b0 100644
--- a/backend/documents_parser/tests/test_summary_pdf_mapper_chain.py
+++ b/backend/documents_parser/tests/test_summary_pdf_mapper_chain.py
@@ -789,6 +789,33 @@ def test_summary_2225_full_chain_sap_within_spec_floor_of_worksheet() -> None:
     assert abs(result.sap_score_continuous - worksheet_unrounded_sap) < _ASHP_COHORT_CHAIN_TOLERANCE
 
 
+def test_summary_2636_full_chain_sap_within_spec_floor_of_worksheet() -> None:
+    # Arrange — cert 2636-0525-2600-0401-2296 (Summary_000898.pdf):
+    # Mitsubishi PUZ-WM50VHA, mid-terrace house with **alt-wall +
+    # cantilever** — the most complex geometry in the ASHP cohort.
+    # Worksheet "SAP value" lodges 86.2641.
+    #
+    # Closed by two combined slices:
+    #   - S0380.12: alt-wall window-location parser fix (walls W/K
+    #     20.5595 → 20.0240 = worksheet exact).
+    #   - S0380.13: cantilever gate accepts "House" descriptive form
+    #     in addition to the schema enum "0" (allowing the Summary
+    #     mapper's descriptive property_type to trigger the cantilever
+    #     detection that slice 102f-prep.9 added on the API path).
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_000898_PDF)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+    epc = EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)
+
+    # Act
+    result = calculate_sap_from_inputs(
+        cert_to_inputs(epc, prices=SAP_10_2_SPEC_PRICES)
+    )
+
+    # Assert — ±0.07 ASHP-cohort spec-floor tolerance.
+    worksheet_unrounded_sap = 86.2641
+    assert abs(result.sap_score_continuous - worksheet_unrounded_sap) < _ASHP_COHORT_CHAIN_TOLERANCE
+
+
 def test_summary_3800_full_chain_sap_within_spec_floor_of_worksheet() -> None:
     # Arrange — cert 3800-8515-0922-3398-3563 (Summary_000901.pdf /
     # dr87-0001-000901.pdf) is the third ASHP cohort cert to close on
diff --git a/domain/sap10_calculator/worksheet/heat_transmission.py b/domain/sap10_calculator/worksheet/heat_transmission.py
index 82077dbb..0baf31a4 100644
--- a/domain/sap10_calculator/worksheet/heat_transmission.py
+++ b/domain/sap10_calculator/worksheet/heat_transmission.py
@@ -109,10 +109,23 @@ _COS_30_DEG: Final[float] = cos(radians(30.0))
 # BP0: 195%), neither of which the worksheet treats as cantilever.
 _CANTILEVER_MIN_AREA_M2: Final[float] = 1.0
 _CANTILEVER_MAX_RATIO: Final[float] = 0.25
-# EPC API `property_type` strings that flag a dwelling as a house (not
-# flat). Cantilever detection only fires for houses — flats with very
-# small floor=0 areas (stairwell access) would otherwise over-count.
-_PROPERTY_TYPE_HOUSE: Final[str] = "0"
+# `property_type` values that flag a dwelling as a house (not flat).
+# Cantilever detection only fires for houses — flats with very small
+# floor=0 areas (stairwell access) would otherwise over-count.
+# The API mapper produces the EPC schema enum-as-string ("0"), the
+# Elmhurst Summary mapper produces the descriptive form ("House"), and
+# the hand-built worksheet fixtures use the descriptive form too. The
+# canonical check below accepts both so the cantilever path fires
+# uniformly regardless of source-mapper encoding.
+_PROPERTY_TYPES_HOUSE: Final[frozenset[str]] = frozenset({"0", "House"})
+
+
+def _is_house(property_type: Optional[str]) -> bool:
+    """True when `epc.property_type` encodes a house (not flat / maisonette
+    / park home). Tolerant of both the API schema's enum-as-string ("0")
+    and the Summary mapper / hand-built fixture descriptive form
+    ("House")."""
+    return property_type in _PROPERTY_TYPES_HOUSE
 
 
 @dataclass(frozen=True)
@@ -765,7 +778,7 @@ def heat_transmission_from_cert(
         # thermal bridges via its area on (31).
         cantilever_area = (
             _round_half_up(geom.get("cantilever_floor_area_m2", 0.0), _AREA_ROUND_DP)
-            if epc.property_type == _PROPERTY_TYPE_HOUSE
+            if _is_house(epc.property_type)
             else 0.0
         )
         if cantilever_area > 0: