diff --git a/backend/documents_parser/elmhurst_extractor.py b/backend/documents_parser/elmhurst_extractor.py
index 11e94fba..a8c9e596 100644
--- a/backend/documents_parser/elmhurst_extractor.py
+++ b/backend/documents_parser/elmhurst_extractor.py
@@ -290,6 +290,10 @@ class ElmhurstSiteNotesExtractor:
             party_wall_type=self._local_str(lines, "Party Wall Type"),
             thickness_mm=thickness_mm,
             insulation_thickness_mm=insulation_thickness_mm,
+            # Summary §7 "Dry-lining: Yes/No" on the main/extension wall.
+            # RdSAP 10 §5.8 + Table 14 dry-lining R=0.17 adjustment. The
+            # alt-wall path reads its own "Alternative Wall N Dry-lining".
+            dry_lined=self._local_bool(lines, "Dry-lining"),
             alternative_walls=self._alternative_walls_from_lines(lines),
             # Summary §7 lodges the per-BP "Curtain Wall Age" line only
             # when `Type: CW Curtain Wall`. Per RdSAP 10 §5.18 (PDF
@@ -548,6 +552,20 @@ class ElmhurstSiteNotesExtractor:
             if self._is_next_rir_row(lines[j]):
                 break
             tokens.append(lines[j])
+            # Every RIR row ends with [default_u, "Yes"/"No", u_value]; the
+            # "Yes"/"No" is the unique u_value_known marker (gable types and
+            # insulation cells never take that value). Stop once we've
+            # appended that flag plus the trailing u_value numeric so the
+            # LAST surface row (no next-row name to bound it) does not
+            # over-read into the following section and shift the trailing
+            # token slotting — which silently zeroed Common Wall 2's
+            # default_u (case 43: 1.90 -> 0.00).
+            if (
+                len(tokens) >= 2
+                and tokens[-2] in ("Yes", "No")
+                and self._RIR_NUMERIC_RE.match(tokens[-1])
+            ):
+                break
         # First two numerics = length, height
         length = float(tokens[0]) if tokens and self._RIR_NUMERIC_RE.match(tokens[0]) else 0.0
         height = float(tokens[1]) if len(tokens) > 1 and self._RIR_NUMERIC_RE.match(tokens[1]) else 0.0
@@ -698,6 +716,7 @@ class ElmhurstSiteNotesExtractor:
                     party_wall_type=ext_party_wall_type,
                     thickness_mm=main_walls.thickness_mm,
                     insulation_thickness_mm=main_walls.insulation_thickness_mm,
+                    dry_lined=main_walls.dry_lined,
                     alternative_walls=self._alternative_walls_from_lines(wall_lines),
                 )
             else:
diff --git a/datatypes/epc/domain/epc_property_data.py b/datatypes/epc/domain/epc_property_data.py
index 1472963d..baf1db00 100644
--- a/datatypes/epc/domain/epc_property_data.py
+++ b/datatypes/epc/domain/epc_property_data.py
@@ -505,7 +505,7 @@ class SapBuildingPart:
     building_part_number: Optional[int] = (
         None  # Not sure how we get this from site notes
     )
-    wall_dry_lined: Optional[bool] = None  # Don't think we have this in site notes
+    wall_dry_lined: Optional[bool] = None  # Summary §7 "Dry-lining: Yes/No"
     wall_thickness_mm: Optional[int] = None
     # Union[str, int]: a numeric mm value when the API lodges
     # `wall_insulation_thickness == "measured"` (resolved from the
diff --git a/datatypes/epc/domain/mapper.py b/datatypes/epc/domain/mapper.py
index d09a46e6..b3fc944f 100644
--- a/datatypes/epc/domain/mapper.py
+++ b/datatypes/epc/domain/mapper.py
@@ -4436,6 +4436,12 @@ def _map_elmhurst_building_part(
         wall_is_basement=_elmhurst_wall_is_basement(walls.wall_type),
         wall_insulation_type=_elmhurst_wall_insulation_int(walls.insulation),
         wall_thickness_measured=not walls.thickness_unknown,
+        # Summary §7 "Dry-lining: Yes" → RdSAP 10 §5.8 Table 14 R=0.17
+        # adjustment in the cascade (`dry_lined=bool(part.wall_dry_lined)`).
+        # Emit None (not False) when undried so the field stays absent for
+        # the non-dry-lined majority (cascade-equivalent: bool(None) == False);
+        # only a lodged "Yes" populates it.
+        wall_dry_lined=walls.dry_lined or None,
         party_wall_construction=_elmhurst_party_wall_construction_int(
             walls.party_wall_type
         ),
diff --git a/datatypes/epc/surveys/elmhurst_site_notes.py b/datatypes/epc/surveys/elmhurst_site_notes.py
index eded346f..4614d33c 100644
--- a/datatypes/epc/surveys/elmhurst_site_notes.py
+++ b/datatypes/epc/surveys/elmhurst_site_notes.py
@@ -94,6 +94,12 @@ class WallDetails:
     # "Insulation Thickness" / "100 mm" line pair when a composite or
     # retrofit insulation is recorded. None when the PDF omits the line.
     insulation_thickness_mm: Optional[int] = None
+    # Summary §7 "Dry-lining: Yes/No" on the main/extension wall (distinct
+    # from the per-alt-wall `AlternativeWall.dry_lined`). Per RdSAP 10
+    # §5.8 + Table 14 a dry-lined uninsulated wall adds R=0.17 m²K/W →
+    # U = 1/(1/U_base + 0.17). Previously unread, so dry-lined solid/
+    # cavity walls were billed at the un-adjusted (higher) base U.
+    dry_lined: bool = False
     # Per-BP curtain-wall installation age, lodged in Summary §7 as
     # "Curtain Wall Age" when `wall_type` is "CW Curtain Wall". Per
     # RdSAP 10 §5.18 (PDF p.48) the curtain-wall U-value keys on this