diff --git a/datatypes/epc/domain/mapper.py b/datatypes/epc/domain/mapper.py
index fa33cf10..70bf7d61 100644
--- a/datatypes/epc/domain/mapper.py
+++ b/datatypes/epc/domain/mapper.py
@@ -711,8 +711,13 @@ class EpcPropertyDataMapper:
                     roof_insulation_thickness=bp.roof_insulation_thickness,
                     sap_room_in_roof=None,
                 )
+                # RdSAP 10 §6.1 — exclude the glazed conservatory BP from the
+                # fabric loop; carried as `sap_conservatory` below. Mirrors the
+                # 19.0 / 21.0.1 path.
                 for bp in schema.sap_building_parts
+                if getattr(bp, "glazed_perimeter", None) is None
             ],
+            sap_conservatory=_api_sap_conservatory(schema.sap_building_parts),
         )
 
     @staticmethod
@@ -1148,8 +1153,13 @@ class EpcPropertyDataMapper:
                     roof_insulation_thickness=bp.roof_insulation_thickness,
                     sap_room_in_roof=None,
                 )
+                # RdSAP 10 §6.1 — exclude the glazed conservatory BP from the
+                # fabric loop; carried as `sap_conservatory` below. Mirrors the
+                # 19.0 / 21.0.1 path.
                 for bp in schema.sap_building_parts
+                if getattr(bp, "glazed_perimeter", None) is None
             ],
+            sap_conservatory=_api_sap_conservatory(schema.sap_building_parts),
         )
 
     @staticmethod
@@ -1371,8 +1381,13 @@ class EpcPropertyDataMapper:
                         else None
                     ),
                 )
+                # RdSAP 10 §6.1 — exclude the glazed conservatory BP from the
+                # fabric loop; carried as `sap_conservatory` below. Mirrors the
+                # 19.0 / 21.0.1 path.
                 for bp in schema.sap_building_parts
+                if getattr(bp, "glazed_perimeter", None) is None
             ],
+            sap_conservatory=_api_sap_conservatory(schema.sap_building_parts),
         )
 
     @staticmethod
@@ -1826,8 +1841,13 @@ class EpcPropertyDataMapper:
                         else None
                     ),
                 )
+                # RdSAP 10 §6.1 — exclude the glazed conservatory BP from the
+                # fabric loop; carried as `sap_conservatory` below. Mirrors the
+                # 19.0 / 21.0.1 path.
                 for bp in schema.sap_building_parts
+                if getattr(bp, "glazed_perimeter", None) is None
             ],
+            sap_conservatory=_api_sap_conservatory(schema.sap_building_parts),
         )
 
     @staticmethod
diff --git a/datatypes/epc/domain/tests/test_from_rdsap_schema.py b/datatypes/epc/domain/tests/test_from_rdsap_schema.py
index f52d1b61..5a2218d3 100644
--- a/datatypes/epc/domain/tests/test_from_rdsap_schema.py
+++ b/datatypes/epc/domain/tests/test_from_rdsap_schema.py
@@ -2533,3 +2533,106 @@ class TestNonSeparatedConservatoryApiMirror19_0:
         # Assert — §6.2: disregarded; no conservatory geometry.
         assert epc.sap_conservatory is None
         assert conservatory_geometry(epc) is None
+
+
+class TestNonSeparatedConservatoryApiMirror20_0_0:
+    """RdSAP 10 §6.1 — the same glazed-BP conservatory, on RdSAP-Schema-20.0.0.
+    Surfaced by the modelling_e2e triage: 5 type-4 certs (e.g. property 725213)
+    failed `NotNullViolation: construction_age_band` because the 20.0.0 schema
+    declared none of the four glazed fields, so the conservatory mapped to a
+    null-age fabric part. Mirrors the 19.0 / 21.0.1 split."""
+
+    def test_from_api_response_splits_out_conservatory_building_part(
+        self,
+    ) -> None:
+        from datatypes.epc.domain.epc_property_data import SapConservatory
+        from domain.sap10_calculator.worksheet.conservatory import (
+            conservatory_geometry,
+        )
+
+        dwelling_part_count = len(
+            EpcPropertyDataMapper.from_api_response(load("20_0_0.json")).sap_building_parts
+        )
+
+        cert = load("20_0_0.json")
+        cert["conservatory_type"] = 4
+        cert["sap_building_parts"].append(
+            {
+                "floor_area": 12.0,
+                "room_height": 1,
+                "double_glazed": "Y",
+                "glazed_perimeter": 9.0,
+            }
+        )
+
+        # Act
+        epc = EpcPropertyDataMapper.from_api_response(cert)
+
+        # Assert — conservatory split out; the glazed BP is NOT a fabric part
+        # (so it never hits the NOT-NULL construction_age_band on persist).
+        assert epc.sap_conservatory == SapConservatory(
+            floor_area_m2=12.0,
+            glazed_perimeter_m=9.0,
+            double_glazed=True,
+            thermally_separated=False,
+            room_height_storeys=1.0,
+        )
+        assert len(epc.sap_building_parts) == dwelling_part_count
+        assert all(
+            bp.construction_age_band is not None for bp in epc.sap_building_parts
+        )
+        assert conservatory_geometry(epc) is not None
+
+    def test_separated_conservatory_lodges_no_glazed_building_part(self) -> None:
+        from domain.sap10_calculator.worksheet.conservatory import (
+            conservatory_geometry,
+        )
+
+        cert = load("20_0_0.json")
+        cert["conservatory_type"] = 2
+
+        # Act
+        epc = EpcPropertyDataMapper.from_api_response(cert)
+
+        # Assert — §6.2: disregarded; no conservatory geometry.
+        assert epc.sap_conservatory is None
+        assert conservatory_geometry(epc) is None
+
+
+@pytest.mark.parametrize("fixture", ["17_0.json", "17_1.json", "18_0.json"])
+def test_gov_mappers_split_non_separated_conservatory(fixture: str) -> None:
+    """RdSAP 10 §6.1 — every gov mapper splits a non-separated conservatory
+    (conservatory_type=4) glazed BP out of the fabric parts and into
+    `sap_conservatory`, so it never persists as a null-age fabric part (the
+    modelling_e2e `construction_age_band` NOT-NULL triage). 19.0 / 20.0.0 /
+    21.0.1 are covered by their own classes; this pins the rest.
+
+    21.0.0 is intentionally excluded: unlike every other gov schema it never
+    adopted the ADR-0027 "every SapBuildingPart field is Optional" treatment, so
+    a sparse conservatory part fails `from_dict` on its required fields. Porting
+    it needs that broader strictness change — tracked as a follow-up; no 21.0.0
+    conservatory cert surfaced in the triage."""
+    from datatypes.epc.domain.epc_property_data import SapConservatory
+
+    base_parts = len(
+        EpcPropertyDataMapper.from_api_response(load(fixture)).sap_building_parts
+    )
+    cert = load(fixture)
+    cert["conservatory_type"] = 4
+    cert["sap_building_parts"].append(
+        {"floor_area": 12.0, "room_height": 1, "double_glazed": "Y", "glazed_perimeter": 9.0}
+    )
+
+    # Act
+    epc = EpcPropertyDataMapper.from_api_response(cert)
+
+    # Assert — split out, not a (null-age) fabric part.
+    assert epc.sap_conservatory == SapConservatory(
+        floor_area_m2=12.0,
+        glazed_perimeter_m=9.0,
+        double_glazed=True,
+        thermally_separated=False,
+        room_height_storeys=1.0,
+    )
+    assert len(epc.sap_building_parts) == base_parts
+    assert all(bp.construction_age_band is not None for bp in epc.sap_building_parts)
diff --git a/datatypes/epc/schema/rdsap_schema_17_0.py b/datatypes/epc/schema/rdsap_schema_17_0.py
index aa1255ca..d66f9c69 100644
--- a/datatypes/epc/schema/rdsap_schema_17_0.py
+++ b/datatypes/epc/schema/rdsap_schema_17_0.py
@@ -120,6 +120,14 @@ class SapBuildingPart:
     wall_insulation_thickness: Optional[str] = None
     floor_insulation_thickness: Optional[str] = None
     flat_roof_insulation_thickness: Optional[Union[str, int]] = None
+    # RdSAP 10 §6.1 — non-separated conservatory glazed-BP fields
+    # ({double_glazed, floor_area, glazed_perimeter, room_height}); declared so
+    # `from_dict` keeps them and the mapper splits the BP into
+    # `EpcPropertyData.sap_conservatory`. Mirrors the 19.0 / 21.0.1 schema.
+    floor_area: Optional[Union[Measurement, int, float]] = None
+    room_height: Optional[Union[Measurement, int, float]] = None
+    double_glazed: Optional[str] = None
+    glazed_perimeter: Optional[Union[Measurement, int, float]] = None
 
 
 @dataclass
diff --git a/datatypes/epc/schema/rdsap_schema_17_1.py b/datatypes/epc/schema/rdsap_schema_17_1.py
index f7f186e6..bbd04b79 100644
--- a/datatypes/epc/schema/rdsap_schema_17_1.py
+++ b/datatypes/epc/schema/rdsap_schema_17_1.py
@@ -106,6 +106,14 @@ class SapBuildingPart:
     # Can be a thickness string (e.g. "100mm") or 0 for uninsulated flat roofs
     roof_insulation_thickness: Optional[Union[str, int]] = None
     wall_insulation_thickness: Optional[str] = None
+    # RdSAP 10 §6.1 — non-separated conservatory glazed-BP fields
+    # ({double_glazed, floor_area, glazed_perimeter, room_height}); declared so
+    # `from_dict` keeps them and the mapper splits the BP into
+    # `EpcPropertyData.sap_conservatory`. Mirrors the 19.0 / 21.0.1 schema.
+    floor_area: Optional[Union[Measurement, int, float]] = None
+    room_height: Optional[Union[Measurement, int, float]] = None
+    double_glazed: Optional[str] = None
+    glazed_perimeter: Optional[Union[Measurement, int, float]] = None
 
 
 @dataclass
diff --git a/datatypes/epc/schema/rdsap_schema_18_0.py b/datatypes/epc/schema/rdsap_schema_18_0.py
index b9e98154..f35f0733 100644
--- a/datatypes/epc/schema/rdsap_schema_18_0.py
+++ b/datatypes/epc/schema/rdsap_schema_18_0.py
@@ -121,6 +121,14 @@ class SapBuildingPart:
     wall_insulation_thickness: Optional[str] = None
     floor_insulation_thickness: Optional[str] = None
     flat_roof_insulation_thickness: Optional[Union[str, int]] = None
+    # RdSAP 10 §6.1 — non-separated conservatory glazed-BP fields
+    # ({double_glazed, floor_area, glazed_perimeter, room_height}); declared so
+    # `from_dict` keeps them and the mapper splits the BP into
+    # `EpcPropertyData.sap_conservatory`. Mirrors the 19.0 / 21.0.1 schema.
+    floor_area: Optional[Union[Measurement, int, float]] = None
+    room_height: Optional[Union[Measurement, int, float]] = None
+    double_glazed: Optional[str] = None
+    glazed_perimeter: Optional[Union[Measurement, int, float]] = None
 
 
 @dataclass
diff --git a/datatypes/epc/schema/rdsap_schema_20_0_0.py b/datatypes/epc/schema/rdsap_schema_20_0_0.py
index 9a4b78f2..395fb9b9 100644
--- a/datatypes/epc/schema/rdsap_schema_20_0_0.py
+++ b/datatypes/epc/schema/rdsap_schema_20_0_0.py
@@ -131,9 +131,12 @@ class SapBuildingPart:
     # ADR-0027: 17/1000 certs lodge a CONSERVATORY-shaped building part carrying
     # only {double_glazed, floor_area, glazed_perimeter, room_height} — none of
     # the wall/roof/floor construction fields below. Following the 21.0.1
-    # precedent every field is Optional, so a conservatory part parses to an
-    # all-None SapBuildingPart; its thermal effect is carried separately by the
-    # cert-level conservatory_type, so the empty part flows through harmlessly.
+    # precedent every field is Optional. RdSAP 10 §6.1: the four glazed fields
+    # are declared so `from_dict` keeps them and the mapper can split this BP out
+    # into `EpcPropertyData.sap_conservatory` (a non-separated conservatory,
+    # `conservatory_type == 4`). Previously undeclared → dropped → the part
+    # mapped to an all-None fabric part that mis-scored AND violated the
+    # NOT-NULL `construction_age_band` column on persist (modelling_e2e triage).
     identifier: Optional[str] = None
     wall_dry_lined: Optional[str] = None
     floor_heat_loss: Optional[int] = None
@@ -153,6 +156,12 @@ class SapBuildingPart:
     wall_insulation_thickness: Optional[str] = None
     floor_insulation_thickness: Optional[str] = None
     flat_roof_insulation_thickness: Optional[Union[str, int]] = None
+    # RdSAP 10 §6.1 — non-separated conservatory glazed-BP fields (see the
+    # class docstring). Mirrors the 19.0 / 21.0.1 schema declaration.
+    floor_area: Optional[Union[Measurement, int, float]] = None
+    room_height: Optional[Union[Measurement, int, float]] = None
+    double_glazed: Optional[str] = None
+    glazed_perimeter: Optional[Union[Measurement, int, float]] = None
 
 
 @dataclass