diff --git a/tests/domain/epc/test_glazing_overlay.py b/tests/domain/epc/test_glazing_overlay.py
index b54e134e..a5a6699e 100644
--- a/tests/domain/epc/test_glazing_overlay.py
+++ b/tests/domain/epc/test_glazing_overlay.py
@@ -7,6 +7,8 @@ window by `_fold_glazing`).
 
 from __future__ import annotations
 
+import pytest
+
 from domain.epc.property_overlays.glazing_overlay import glazing_overlay_for
 
 
@@ -18,3 +20,24 @@ def test_double_glazing_post_2002_overlays_its_glazing_code() -> None:
     assert simulation is not None
     assert simulation.glazing is not None
     assert simulation.glazing.glazing_type == 2
+
+
+@pytest.mark.parametrize(
+    ("glazing_value", "code"),
+    [
+        ("Single glazing", 1),
+        ("Double glazing, pre-2002", 3),
+        ("Triple glazing, 2002 or later", 9),
+        ("Triple glazing, pre-2002", 6),
+    ],
+)
+def test_glazing_types_decode_to_their_sap_codes(
+    glazing_value: str, code: int
+) -> None:
+    # Act
+    simulation = glazing_overlay_for(glazing_value, 0)
+
+    # Assert
+    assert simulation is not None
+    assert simulation.glazing is not None
+    assert simulation.glazing.glazing_type == code