diff --git a/tests/repositories/epc/test_epc_round_trip.py b/tests/repositories/epc/test_epc_round_trip.py
index f32e40b1..ed49b6d9 100644
--- a/tests/repositories/epc/test_epc_round_trip.py
+++ b/tests/repositories/epc/test_epc_round_trip.py
@@ -86,6 +86,42 @@ def test_non_separated_conservatory_round_trips(db_engine: Engine) -> None:
     assert reloaded == original
 
 
+def test_floor_dimension_heat_loss_flags_round_trip(db_engine: Engine) -> None:
+    # SAP 10.2 §3.3 — `is_exposed_floor` and `is_above_partially_heated_space`
+    # are heat-loss flags on a `SapFloorDimension`: the calculator routes a floor
+    # over outside air / over a partially-heated space through a different
+    # U-value path. They had no `epc_floor_dimension` column, so a True flag
+    # round-tripped back to the `False` default and silently flipped the floor's
+    # heat loss (persist != score). We force both True on a clean fixture so the
+    # ONLY thing that can break deep-equality is these two flags.
+    from dataclasses import replace
+
+    # Arrange — a green fixture with a floor dimension, both flags forced True.
+    original = _load_epc("RdSAP-Schema-21.0.0")
+    assert original.sap_building_parts, "fixture must have a building part"
+    bp0 = original.sap_building_parts[0]
+    assert bp0.sap_floor_dimensions, "fixture building part must have a floor dimension"
+    dim0 = replace(
+        bp0.sap_floor_dimensions[0],
+        is_exposed_floor=True,
+        is_above_partially_heated_space=True,
+    )
+    bp0 = replace(bp0, sap_floor_dimensions=[dim0, *bp0.sap_floor_dimensions[1:]])
+    original = replace(
+        original, sap_building_parts=[bp0, *original.sap_building_parts[1:]]
+    )
+
+    # Act
+    with Session(db_engine) as session:
+        epc_property_id = EpcPostgresRepository(session).save(original)
+        session.commit()
+    with Session(db_engine) as session:
+        reloaded = EpcPostgresRepository(session).get(epc_property_id)
+
+    # Assert — both flags survive the round-trip, deep-equal.
+    assert reloaded == original
+
+
 def test_building_part_wall_insulation_thickness_preserves_int(
     db_engine: Engine,
 ) -> None: