diff --git a/backend/ecmk_fetcher/tests/test_xml_processor.py b/backend/ecmk_fetcher/tests/test_xml_processor.py
index 1a308177..3fd9e45e 100644
--- a/backend/ecmk_fetcher/tests/test_xml_processor.py
+++ b/backend/ecmk_fetcher/tests/test_xml_processor.py
@@ -172,6 +172,57 @@ def test_parse_rdsap_contract():
     }
 
 
+ND_THICKNESS_XML = """<RdSAP-Report xmlns="https://epbr.digital.communities.gov.uk/xsd/rdsap">
+<Report-Header>
+    <Property>
+        <Address>
+            <Address-Line-1>1</Address-Line-1>
+            <Post-Town>Somewhere</Post-Town>
+            <Postcode>AB1 2CD</Postcode>
+        </Address>
+    </Property>
+</Report-Header>
+<SAP-Data>
+    <SAP-Property-Details>
+        <Property-Type>0</Property-Type>
+        <SAP-Building-Parts>
+            <SAP-Building-Part>
+                <Identifier>Main Dwelling</Identifier>
+                <Roof-Construction>4</Roof-Construction>
+                <Roof-Insulation-Location>2</Roof-Insulation-Location>
+                <Roof-Insulation-Thickness>ND</Roof-Insulation-Thickness>
+                <SAP-Floor-Dimensions>
+                    <SAP-Floor-Dimension>
+                        <Heat-Loss-Perimeter quantity="metres">10.0</Heat-Loss-Perimeter>
+                        <Room-Height quantity="metres">2.5</Room-Height>
+                        <Total-Floor-Area quantity="square metres">50.0</Total-Floor-Area>
+                        <Floor>0</Floor>
+                        <Party-Wall-Length>0</Party-Wall-Length>
+                    </SAP-Floor-Dimension>
+                </SAP-Floor-Dimensions>
+            </SAP-Building-Part>
+        </SAP-Building-Parts>
+    </SAP-Property-Details>
+</SAP-Data>
+</RdSAP-Report>
+"""
+
+
+def test_parse_rdsap_nd_thickness():
+    # 'ND' (not determined) is a valid value in the wild for Roof-Insulation-Thickness
+    # — it should be retained as-is rather than raising
+
+    # arrange + act
+    result: SapPropertyDetails = parse_rdsap(ND_THICKNESS_XML)
+
+    # assert
+    assert result["building_parts"][0]["roof"] == {
+        "construction": 4,
+        "insulation_location": 2,
+        "insulation_thickness_mm": "ND",
+    }
+
+
 def test_flatten_full():
     # Two building parts; Main Dwelling has two floors + full roof,
     # Extension has one floor + partial roof (no thickness)
diff --git a/datatypes/epc/domain/field_mappings.py b/datatypes/epc/domain/field_mappings.py
index 55156d3d..cc0f9067 100644
--- a/datatypes/epc/domain/field_mappings.py
+++ b/datatypes/epc/domain/field_mappings.py
@@ -1 +1,3 @@
 PROPERTY_TYPE_LOOKUP = {0: "House", 1: "Bungalow", 2: "Flat", 3: "Maisonette"}
+ROOF_CONSTRUCTION_LOOKUP = {}
+ROOF_INSULATION_LOCATION_LOOKUP = {}