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 223075f6..6388767a 100644
--- a/backend/documents_parser/tests/test_summary_pdf_mapper_chain.py
+++ b/backend/documents_parser/tests/test_summary_pdf_mapper_chain.py
@@ -557,6 +557,35 @@ def test_api_9501_photovoltaic_array_surfaced() -> None:
     assert arrays[0].overshading == 1  # RdSAP: None or very little
 
 
+_API_0380_JSON = (
+    Path(__file__).parents[3]
+    / "domain/sap10_calculator/rdsap/tests/fixtures/golden"
+    / "0380-2471-3250-2596-8761.json"
+)
+
+
+def test_api_0380_glazing_type_14_resolves_to_post_2022_dg_u_value() -> None:
+    # Arrange — cert 0380 (ASHP semi-detached bungalow, worksheet SAP
+    # 88.5104) lodges glazing_type=14 on all windows. The worksheet
+    # uses U=1.3258 (post-curtain) for line (27), which back-calculates
+    # to a raw U=1.40 — the SAP10.2 Table 24 row for "Double or triple
+    # glazed, 2022 or later". Code 13 in our existing dict carries the
+    # same U/g values; code 14 is the schema sibling for the same
+    # post-2022 product family (DG sealed-unit variants differ in
+    # the cert lodgement but agree on the spec U-value).
+    doc = json.loads(_API_0380_JSON.read_text())
+    epc = EpcPropertyDataMapper.from_api_response(doc)
+
+    # Act — pick any window (cert 0380 lodges only glazing_type=14).
+    w = epc.sap_windows[0]
+    td = w.window_transmission_details
+
+    # Assert
+    assert td is not None
+    assert abs(td.u_value - 1.40) <= 1e-4
+    assert abs(td.solar_transmittance - 0.72) <= 1e-4
+
+
 def test_api_9501_room_in_roof_surfaces_populated() -> None:
     # Arrange — cert 9501's API JSON lodges measured RR detail under
     # `sap_room_in_roof.room_in_roof_details`: two gable walls
diff --git a/datatypes/epc/domain/mapper.py b/datatypes/epc/domain/mapper.py
index b7140ae7..28493ebe 100644
--- a/datatypes/epc/domain/mapper.py
+++ b/datatypes/epc/domain/mapper.py
@@ -2286,6 +2286,14 @@ _API_GLAZING_TYPE_TO_TRANSMISSION: Dict[int, tuple[float, float, float]] = {
     2: (2.0, 0.72, 0.70),    # Double glazed, England/Wales 2002+ (pre-2022)
     3: (2.8, 0.76, 0.70),    # Double glazed, pre-2002 (12mm gap default)
     13: (1.4, 0.72, 0.70),   # Double glazed, Argon-filled post-2022
+    14: (1.4, 0.72, 0.70),   # Double or triple glazed, post-2022
+                             # (Table 24 last row: 2022+ E/W / 2023+ Sc
+                             # / 2022+ NI — same U/g as code 13 per
+                             # spec; the integer codes 13/14 are
+                             # schema siblings within the post-2022
+                             # product family. Cert 0380 lodges code
+                             # 14 on all windows; worksheet uses U=1.4
+                             # = post-curtain 1.3258.)
 }