diff --git a/domain/epc/property_overlays/glazing_overlay.py b/domain/epc/property_overlays/glazing_overlay.py
index d692181d8..81733461c 100644
--- a/domain/epc/property_overlays/glazing_overlay.py
+++ b/domain/epc/property_overlays/glazing_overlay.py
@@ -24,6 +24,7 @@ _GLAZING_CODES: dict[str, int] = {
     "Double glazing, pre-2002": 3,
     "Triple glazing, pre-2002": 6,
     "Triple glazing, 2002 or later": 9,
+    "Secondary glazing": 5,
 }
 
 
diff --git a/domain/epc/property_overrides/glazing_type.py b/domain/epc/property_overrides/glazing_type.py
index 8724f5b5e..4a4ef96b3 100644
--- a/domain/epc/property_overrides/glazing_type.py
+++ b/domain/epc/property_overrides/glazing_type.py
@@ -28,4 +28,8 @@ class GlazingType(Enum):
     # which windows are which (ADR-0042 amendment, #1376). The FE-owned pgEnum
     # gains this member via a Drizzle migration.
     MIXED = "Mixed glazing"
+    # Secondary glazing (a pane added inside the original window) is era-free like
+    # SINGLE — SAP10 glazing code 5, U = 2.9 regardless of install year. The
+    # FE-owned pgEnum gains this member via assessment-model#345.
+    SECONDARY = "Secondary glazing"
     UNKNOWN = "Unknown"