diff --git a/domain/epc/property_overlays/roof_type_overlay.py b/domain/epc/property_overlays/roof_type_overlay.py
index bf47c67cd..9fa8f3024 100644
--- a/domain/epc/property_overlays/roof_type_overlay.py
+++ b/domain/epc/property_overlays/roof_type_overlay.py
@@ -29,6 +29,9 @@ from domain.modelling.simulation import BuildingPartOverlay, EpcSimulation
 _LOFT_MM = re.compile(r"(\d+)\+?\s*mm loft insulation")
 # A flat roof carries no loft, so its depth reads "N mm insulation" (no "loft").
 _FLAT_MM = re.compile(r"(\d+)\+?\s*mm insulation")
+# A sloping ceiling's depth reads the same "N mm insulation" shape (no "loft");
+# the "sloping ceiling" prefix, not the suffix, distinguishes it from a flat roof.
+_SLOPING_MM = re.compile(r"(\d+)\+?\s*mm insulation")
 
 
 def roof_overlay_for(
@@ -53,9 +56,17 @@ def _overlay_for(roof_type_value: str) -> Optional[BuildingPartOverlay]:
     if roof_type_value.startswith("Pitched, sloping ceiling"):
         # ADR-0066: a slope-following ceiling (gov-API roof_construction 8) has no
         # loft void. Assert the sloping-ceiling shape so the calculator's
-        # `is_pitched_sloping_ceiling` drives the Table 18 col (3) age-band default
-        # ("as built"), never the loft ladder. Leave thickness None here.
-        return BuildingPartOverlay(roof_construction_type="Pitched, sloping ceiling")
+        # `is_pitched_sloping_ceiling` keys off "sloping ceiling" in the string.
+        # A known depth ("N mm insulation") rides into the overlay and scores on
+        # Table 17 col (1a) "insulated slope"; "as built" leaves thickness None so
+        # the Table 18 col (3) age-band default drives it. Never the loft ladder.
+        sloping_depth = _SLOPING_MM.search(roof_type_value)
+        return BuildingPartOverlay(
+            roof_construction_type="Pitched, sloping ceiling",
+            roof_insulation_thickness=(
+                int(sloping_depth.group(1)) if sloping_depth is not None else None
+            ),
+        )
     if roof_type_value.startswith("Flat,"):
         flat_depth = _FLAT_MM.search(roof_type_value)
         if flat_depth is not None: