diff --git a/backend/documents_parser/tests/test_summary_pdf_mapper_chain.py b/backend/documents_parser/tests/test_summary_pdf_mapper_chain.py
index d3ed87d6..66f0172e 100644
--- a/backend/documents_parser/tests/test_summary_pdf_mapper_chain.py
+++ b/backend/documents_parser/tests/test_summary_pdf_mapper_chain.py
@@ -1489,6 +1489,7 @@ def test_elmhurst_glazing_label_full_coverage_per_sap10_table_6b() -> None:
         "Double post or during 2022": 5,
         "Secondary glazing": 7,
         "Secondary glazing - Normal emissivity": 11,
+        "Secondary glazing - Low emissivity": 12,
         "Triple pre 2002": 10,
         "Triple between 2002 and 2021": 9,
         "Triple post or during 2022": 6,
diff --git a/datatypes/epc/domain/mapper.py b/datatypes/epc/domain/mapper.py
index 71df85c0..32765df1 100644
--- a/datatypes/epc/domain/mapper.py
+++ b/datatypes/epc/domain/mapper.py
@@ -5083,6 +5083,12 @@ _ELMHURST_GLAZING_LABEL_TO_SAP10: Dict[str, int] = {
     # fixture (Summary_001431 §11 Window 9).
     "Secondary glazing": 7,
     "Secondary glazing - Normal emissivity": 11,
+    # RdSAP-21 glazed_type 12 "secondary glazing, low emissivity" — the
+    # low-E sibling of code 11. Cascade code 12 carries g_L=0.80 / g⊥=0.76
+    # (identical daylight/solar bucket to 7 and 11; the lodged U/g drive
+    # §3/§6). Mapped symmetrically with the "Normal emissivity" variant so
+    # the whole secondary-glazing family is covered.
+    "Secondary glazing - Low emissivity": 12,
     # RdSAP-21 row "triple glazing, installed pre-2002" (cascade code 10,
     # g_L=0.70, g⊥=0.68 — same triple-glazed daylight/solar bucket as the
     # other triple variants {6, 8, 9, 14}). The lodged manufacturer