diff --git a/domain/modelling/generators/wall_recommendation.py b/domain/modelling/generators/wall_recommendation.py
index 2c5622413..b3182ba28 100644
--- a/domain/modelling/generators/wall_recommendation.py
+++ b/domain/modelling/generators/wall_recommendation.py
@@ -12,6 +12,7 @@ from datatypes.epc.domain.epc_property_data import (
     EpcPropertyData,
 )
 from domain.building_geometry import gross_heat_loss_wall_area
+from domain.modelling.generators.wall_u_value_gate import wall_insulation_lowers_u
 from domain.modelling.measure_type import MeasureType
 from domain.modelling.recommendation import Cost, MeasureOption, Recommendation
 from domain.modelling.simulation import BuildingPartOverlay, EpcSimulation
@@ -46,6 +47,14 @@ def recommend_cavity_wall(
     ):
         return None
 
+    # Wall U-Value Gate (ADR-0051): withhold the fill when it cannot lower the
+    # wall's derived U — e.g. an at-regs modern age band, where the as-built and
+    # filled-cavity cascades resolve to the same (or a no-better) value.
+    if not wall_insulation_lowers_u(
+        main, epc.country_code, insulation_type=_FILLED_CAVITY
+    ):
+        return None
+
     product = products.get(_CAVITY_MEASURE_TYPE)
     wall_area: float = gross_heat_loss_wall_area(epc, BuildingPartIdentifier.MAIN)
     cost = Cost(