diff --git a/tests/domain/epc/test_glazing_overlay.py b/tests/domain/epc/test_glazing_overlay.py
index 9668e3aa..d65220e7 100644
--- a/tests/domain/epc/test_glazing_overlay.py
+++ b/tests/domain/epc/test_glazing_overlay.py
@@ -10,6 +10,10 @@ from __future__ import annotations
 import pytest
 
 from domain.epc.property_overlays.glazing_overlay import glazing_overlay_for
+from domain.modelling.scoring.overlay_applicator import apply_simulations
+from tests.domain.sap10_calculator.worksheet._elmhurst_worksheet_000490 import (
+    build_epc,
+)
 
 
 def test_double_glazing_post_2002_overlays_its_glazing_code() -> None:
@@ -50,3 +54,20 @@ def test_unresolvable_glazing_produces_no_overlay(glazing_value: str) -> None:
 
     # Assert
     assert simulation is None
+
+
+def test_glazing_override_remaps_every_window_and_clears_lodged_u() -> None:
+    # Arrange — baseline windows are double glazed (code 2, lodged U 2.8); the
+    # landlord corrects the whole dwelling to single glazing.
+    baseline = build_epc()
+    assert len(baseline.sap_windows) > 1
+    overlay = glazing_overlay_for("Single glazing", 0)
+    assert overlay is not None
+
+    # Act
+    result = apply_simulations(baseline, [overlay])
+
+    # Assert — every window flips to single (code 1) and its lodged transmission
+    # U is cleared so the Table-24 cascade re-derives U from the new type.
+    assert all(w.glazing_type == 1 for w in result.sap_windows)
+    assert all(w.window_transmission_details is None for w in result.sap_windows)