diff --git a/datatypes/epc/domain/tests/test_from_site_notes.py b/datatypes/epc/domain/tests/test_from_site_notes.py
index 717b6c4d6..8ecfa96c2 100644
--- a/datatypes/epc/domain/tests/test_from_site_notes.py
+++ b/datatypes/epc/domain/tests/test_from_site_notes.py
@@ -433,6 +433,23 @@ class TestCylinderInsulationTypeCoding:
         assert result.sap_heating is not None
         assert result.sap_heating.cylinder_insulation_type == 1
 
+    def test_loose_jacket_codes_to_jacket(self) -> None:
+        # Arrange — "Loose jacket" → code 2 (gov-API coding; Elmhurst
+        # "Jacket" sibling). SAP 10.2 Table 2 Note 1 bills a loose jacket a
+        # separate, ~2× higher storage-loss factor than factory foam.
+        data = load("pashub_rdsap_site_notes_example1.json")
+        data["heating_and_hot_water"]["water_heating"]["insulation_type"] = (
+            "Loose jacket"
+        )
+        survey = from_dict(PasHubRdSapSiteNotes, data)
+
+        # Act
+        result = EpcPropertyDataMapper.from_site_notes(survey)
+
+        # Assert
+        assert result.sap_heating is not None
+        assert result.sap_heating.cylinder_insulation_type == 2
+
     def test_unknown_label_strict_raises(self) -> None:
         # Arrange
         data = load("pashub_rdsap_site_notes_example1.json")