diff --git a/datatypes/epc/domain/tests/test_from_site_notes.py b/datatypes/epc/domain/tests/test_from_site_notes.py
index 58956d9a8..5c8d18233 100644
--- a/datatypes/epc/domain/tests/test_from_site_notes.py
+++ b/datatypes/epc/domain/tests/test_from_site_notes.py
@@ -167,16 +167,30 @@ class TestRoomInRoofMapping:
         assert rir.construction_age_band == "B"
         surfaces = rir.detailed_surfaces
         assert surfaces is not None
+        # Common walls lodge as Detailed-mode stud walls (Table 17 col 3) —
+        # "common_wall" is a §3.9.2 Simplified-Type-2-only concept; every
+        # worksheet-validated Detailed fixture uses stud_wall for this low
+        # internal wall.
         kinds_areas = [(s.kind, round(s.area_m2, 2)) for s in surfaces]
         assert kinds_areas == [
             ("gable_wall_external", round(6.64 * 2.74, 2)),
             ("gable_wall", round(6.64 * 2.74, 2)),
             ("slope", round(4.94 * 1.73, 2)),
             ("slope", round(5.0 * 2.95, 2)),
-            ("common_wall", round(4.94 * 1.45, 2)),
-            ("common_wall", round(4.94 * 1.3, 2)),
+            ("stud_wall", round(4.94 * 1.45, 2)),
+            ("stud_wall", round(4.94 * 1.3, 2)),
             ("flat_ceiling", round(4.94 * 5.17, 2)),
         ]
+        # PasHub lodges roof insulation once at roof-space level (the fixture's
+        # "Joists"/100mm) — thread it into the roof-going surfaces so they
+        # aren't billed at the Table 18 "unknown" full-uninsulated default
+        # while the same survey says the roof is insulated. Gables keep None
+        # (walls — insulation described by the wall fields, not the loft).
+        by_kind = {s.kind: s.insulation_thickness_mm for s in surfaces}
+        assert by_kind["slope"] == 100
+        assert by_kind["stud_wall"] == 100
+        assert by_kind["flat_ceiling"] == 100
+        assert by_kind["gable_wall"] is None
 
     def test_no_rooms_in_roof_stays_absent(self) -> None:
         # Arrange — the fixture as lodged (rooms_in_roof=false).