diff --git a/datatypes/epc/domain/tests/test_from_site_notes.py b/datatypes/epc/domain/tests/test_from_site_notes.py
index b5bc4f29b..77c7ed4fd 100644
--- a/datatypes/epc/domain/tests/test_from_site_notes.py
+++ b/datatypes/epc/domain/tests/test_from_site_notes.py
@@ -297,6 +297,56 @@ class TestRoomInRoofMapping:
         ]
 
 
+class TestWallDryLinedMapping:
+    """A surveyed "Wall Dry-Lined? Yes" must reach
+    `sap_building_parts[*].wall_dry_lined` — the flag the wall-U cascade
+    reads for the RdSAP10 §5.8 / Table 14 adjustment (1/(1/U + 0.17)).
+    Dropped, a dry-lined wall is billed at the full uninsulated Table 6 U
+    (19% of the Guinness accuracy cohort lodges a "Yes"; already mapped on
+    the Elmhurst/API path, silently None on the pashub site-notes path)."""
+
+    def test_main_building_answer_reaches_building_part(self) -> None:
+        # Arrange
+        data = load("pashub_rdsap_site_notes_example1.json")
+        data["building_construction"]["main_building"]["dry_lined"] = True
+        survey = from_dict(PasHubRdSapSiteNotes, data)
+
+        # Act
+        result = EpcPropertyDataMapper.from_site_notes(survey)
+
+        # Assert
+        assert result.sap_building_parts[0].wall_dry_lined is True
+
+    def test_extension_answer_reaches_building_part(self) -> None:
+        # Arrange
+        data = load("pashub_rdsap_site_notes_example2.json")
+        data["building_construction"]["extensions"][0]["dry_lined"] = False
+        survey = from_dict(PasHubRdSapSiteNotes, data)
+
+        # Act
+        result = EpcPropertyDataMapper.from_site_notes(survey)
+
+        # Assert
+        extension_part = next(
+            bp
+            for bp in result.sap_building_parts
+            if bp.identifier != BuildingPartIdentifier.MAIN
+        )
+        assert extension_part.wall_dry_lined is False
+
+    def test_not_asked_stays_unknown(self) -> None:
+        # Arrange — the fixture as lodged (no "Wall Dry-Lined?" answer).
+        survey = from_dict(
+            PasHubRdSapSiteNotes, load("pashub_rdsap_site_notes_example1.json")
+        )
+
+        # Act
+        result = EpcPropertyDataMapper.from_site_notes(survey)
+
+        # Assert — unknown, NOT a "No".
+        assert result.sap_building_parts[0].wall_dry_lined is None
+
+
 class TestSystemBuildWallIsNotBasement:
     """RdSAP wall-construction code 6 is overloaded: PasHub "System Build
     (i.e Any Other)" maps to 6, but 6 doubles as the gov-API basement-wall