diff --git a/domain/epc/property_overrides/roof_party_ceiling_guard.py b/domain/epc/property_overrides/roof_party_ceiling_guard.py
index 97cdb09b1..c4b446c3e 100644
--- a/domain/epc/property_overrides/roof_party_ceiling_guard.py
+++ b/domain/epc/property_overrides/roof_party_ceiling_guard.py
@@ -1,9 +1,23 @@
 from __future__ import annotations
 
+import re
 from typing import Optional
 
 from domain.epc.property_overrides.roof_type import RoofType
 
+# The roof-type token (before any ``: <insulation>`` suffix), normalised to lower
+# alphanumerics, → its party-ceiling RoofType member. Normalising strips spacing
+# and case so both ``"another dwelling above"`` and ``"anotherdwellingabove"``
+# match the same marker.
+_PARTY_CEILING_MARKERS: dict[str, RoofType] = {
+    "anotherdwellingabove": RoofType.ADJACENT_ANOTHER_DWELLING_ABOVE,
+}
+
+
+def _normalise_roof_token(description: str) -> str:
+    token = description.split(":", 1)[0]
+    return re.sub(r"[^a-z0-9]", "", token.lower())
+
 
 def roof_party_ceiling_guard(description: str) -> Optional[RoofType]:
     """Deterministically resolve a party-ceiling roof description to its RoofType.
@@ -20,4 +34,4 @@ def roof_party_ceiling_guard(description: str) -> Optional[RoofType]:
     that is not a party-ceiling marker so the LLM classifier still handles it
     (#1376).
     """
-    raise NotImplementedError
+    return _PARTY_CEILING_MARKERS.get(_normalise_roof_token(description))