diff --git a/backend/documents_parser/tests/test_extractor.py b/backend/documents_parser/tests/test_extractor.py
index 444742b48..934488614 100644
--- a/backend/documents_parser/tests/test_extractor.py
+++ b/backend/documents_parser/tests/test_extractor.py
@@ -198,6 +198,29 @@ class TestBuildingConstruction:
         assert construction.extensions is not None
         assert construction.extensions[0].id == 1
 
+    def test_wall_dry_lined_answers_are_captured(self) -> None:
+        # Arrange / Act — fixture 7 lodges "Wall Dry-Lined?" per building
+        # part: Main "No", Extension 1 "Yes", Extension 2 "Yes". Dropped, a
+        # dry-lined wall is billed at the full uninsulated Table 6 U instead
+        # of the RdSAP10 §5.8 / Table 14 dry-lining-adjusted value (19% of
+        # the Guinness accuracy cohort lodges a "Yes").
+        construction = PasHubRdSapSiteNotesExtractor(
+            load_text_fixture_7()
+        ).extract_building_construction()
+
+        # Assert
+        assert construction.main_building.dry_lined is False
+        assert construction.extensions is not None
+        assert [e.dry_lined for e in construction.extensions] == [True, True]
+
+    def test_wall_dry_lined_not_asked_stays_unknown(
+        self, construction: BuildingConstruction
+    ) -> None:
+        # Fixture 1 never asks "Wall Dry-Lined?" — unknown, NOT a "No".
+        assert construction.main_building.dry_lined is None
+        assert construction.extensions is not None
+        assert construction.extensions[0].dry_lined is None
+
     def test_full_building_construction(
         self, construction: BuildingConstruction
     ) -> None:
diff --git a/datatypes/epc/surveys/pashub_rdsap_site_notes.py b/datatypes/epc/surveys/pashub_rdsap_site_notes.py
index aa278425e..33c691e5a 100644
--- a/datatypes/epc/surveys/pashub_rdsap_site_notes.py
+++ b/datatypes/epc/surveys/pashub_rdsap_site_notes.py
@@ -47,6 +47,9 @@ class MainBuildingConstruction:
     wall_thickness_mm: Optional[int]
     party_wall_construction_type: str
     filled_cavity_indicators: Optional[str] = None
+    # "Wall Dry-Lined?" Yes/No; None when the survey doesn't ask (e.g.
+    # non-masonry system build).
+    dry_lined: Optional[bool] = None
 
 
 @dataclass
@@ -62,6 +65,8 @@ class ExtensionConstruction:
     wall_thickness_mm: Optional[int]
     party_wall_construction_type: str
     filled_cavity_indicators: Optional[str] = None
+    # "Wall Dry-Lined?" Yes/No; None when the survey doesn't ask.
+    dry_lined: Optional[bool] = None
 
 
 @dataclass