diff --git a/domain/modelling/generators/roof_recommendation.py b/domain/modelling/generators/roof_recommendation.py
index 9a3fff36..0d4f356d 100644
--- a/domain/modelling/generators/roof_recommendation.py
+++ b/domain/modelling/generators/roof_recommendation.py
@@ -49,6 +49,16 @@ def recommend_roof_insulation(
         for part in epc.sap_building_parts
         if part.identifier is BuildingPartIdentifier.MAIN
     )
+
+    # Room-in-roof safety guard (ADR-0021): a room-in-roof carries its
+    # insulation on its own sloping/stud/gable surfaces (RdSAP 10 §3.10, Table
+    # 17/18), which the loft/sloping overlay's flat `roof_insulation_thickness`
+    # bump cannot model. Without this guard a RR with an uninsulated loft would
+    # fall through to the loft fallback and mis-recommend loft insulation.
+    # Defer until a dedicated RR branch lands.
+    if main.sap_room_in_roof is not None:
+        return None
+
     roof_type: str = (main.roof_construction_type or "").lower()
 
     # Dispatch by roof type (ADR-0021). Order matters: a sloping ceiling is
diff --git a/tests/domain/modelling/test_roof_recommendation.py b/tests/domain/modelling/test_roof_recommendation.py
index fa27d03b..63f28ce6 100644
--- a/tests/domain/modelling/test_roof_recommendation.py
+++ b/tests/domain/modelling/test_roof_recommendation.py
@@ -7,6 +7,7 @@ from datatypes.epc.domain.epc_property_data import (
     BuildingPartIdentifier,
     EpcPropertyData,
     SapBuildingPart,
+    SapRoomInRoof,
 )
 from domain.modelling.scoring.overlay_applicator import apply_simulations
 from domain.modelling.product import Product
@@ -63,6 +64,25 @@ def test_already_insulated_loft_yields_no_recommendation() -> None:
     assert recommendation is None
 
 
+def test_room_in_roof_yields_no_recommendation_pending_a_dedicated_branch() -> None:
+    # Arrange — an uninsulated loft the fallback would otherwise top up, but the
+    # part is a room-in-roof. The simple loft/sloping overlay can't model RR
+    # insulation (its sloping/stud/gable surfaces carry their own U-values via
+    # Table 17/18), so the generator must defer rather than mis-fire loft.
+    baseline: EpcPropertyData = build_epc()
+    main: SapBuildingPart = _part(baseline, BuildingPartIdentifier.MAIN)
+    main.roof_insulation_thickness = 0
+    main.sap_room_in_roof = SapRoomInRoof(floor_area=9.0, construction_age_band="D")
+
+    # Act
+    recommendation: Recommendation | None = recommend_roof_insulation(
+        baseline, _StubProducts()
+    )
+
+    # Assert
+    assert recommendation is None
+
+
 def test_loft_option_carries_cost_from_roof_area_and_product() -> None:
     # Arrange
     baseline: EpcPropertyData = build_epc()  # MAIN roof area 14.85 m^2