diff --git a/packages/domain/src/domain/sap/worksheet/tests/_elmhurst_worksheet_000474.py b/packages/domain/src/domain/sap/worksheet/tests/_elmhurst_worksheet_000474.py
index 19a2c65e..a605fda3 100644
--- a/packages/domain/src/domain/sap/worksheet/tests/_elmhurst_worksheet_000474.py
+++ b/packages/domain/src/domain/sap/worksheet/tests/_elmhurst_worksheet_000474.py
@@ -64,11 +64,14 @@ def build_epc() -> EpcPropertyData:
         wall_thickness_measured=False,
         party_wall_construction=0,
         sap_floor_dimensions=[
+            # Ext1 hangs off the main from the first storey upward — its
+            # lowest dimension is an exposed timber floor (Table 20).
             SapFloorDimension(
                 room_height_m=2.81,  # lowest of ext, internal
                 total_floor_area_m2=15.04,
                 party_wall_length_m=3.56, heat_loss_perimeter_m=8.46,
                 floor=0,
+                is_exposed_floor=True,
             ),
             SapFloorDimension(
                 room_height_m=3.13,  # = 2.88 + 0.25
@@ -163,3 +166,18 @@ LINE_31_TOTAL_EXTERNAL_AREA_M2: float = 153.3900
 LINE_33_FABRIC_HEAT_LOSS_W_PER_K: float = 209.1084
 LINE_36_THERMAL_BRIDGING_W_PER_K: float = 23.0085
 LINE_37_TOTAL_FABRIC_HEAT_LOSS_W_PER_K: float = 232.1169
+
+# §3 windows + doors — values from the Elmhurst worksheet §3 table.
+# Two window types share the dwelling:
+#   Type 1 (post-2002 double-glazed, PVC, g=0.72): 6.22 m² at raw U=2.0,
+#           U_eff=1.8519
+#   Type 2 (pre-2002  double-glazed, PVC, g=0.76): 5.50 m² at raw U=2.8,
+#           U_eff=2.5180
+# Worksheet windows_w_per_k = 25.3675. Aggregating to a single area-
+# weighted raw U with the curtain-resistance transform applied reproduces
+# the total to better than 0.05 W/K:
+#   U_eff_target = 25.3675 / 11.72 = 2.1645
+#   raw U = 1/(1/2.1645 - 0.04) ≈ 2.37
+WINDOW_TOTAL_AREA_M2: float = 11.72
+WINDOW_AVG_RAW_U_VALUE: float = 2.37
+DOOR_COUNT: int = 2  # cascade default 1.85 m²/door → 3.70 m² matches worksheet
diff --git a/packages/domain/src/domain/sap/worksheet/tests/test_heat_transmission.py b/packages/domain/src/domain/sap/worksheet/tests/test_heat_transmission.py
index ea4e31df..c2e48d72 100644
--- a/packages/domain/src/domain/sap/worksheet/tests/test_heat_transmission.py
+++ b/packages/domain/src/domain/sap/worksheet/tests/test_heat_transmission.py
@@ -1179,6 +1179,34 @@ def test_section_3_non_rr_line_31_and_36_match_elmhurst_worksheet(
     )
 
 
+def test_section_3_line_33_and_line_37_match_elmhurst_worksheet_000474() -> None:
+    """Full §3 fabric heat loss for Elmhurst U985-0001-000474. Mid-terrace
+    with 3 building parts (Main + 2 extensions). Ext1 is the exposed-timber
+    upper floor (same shape as 000490 Ext1). Two window types share an
+    area-weighted raw U-value when aggregated (post-2002 raw 2.0 mixed
+    with pre-2002 raw 2.8); reproducing the worksheet's per-type sum of
+    25.37 W/K to 0.1 W/K is sufficient given the curtain-resistance
+    transform is non-linear."""
+    # Arrange
+    epc = _w000474.build_epc()
+
+    # Act
+    result = heat_transmission_from_cert(
+        epc,
+        window_total_area_m2=_w000474.WINDOW_TOTAL_AREA_M2,
+        window_avg_u_value=_w000474.WINDOW_AVG_RAW_U_VALUE,
+        door_count=_w000474.DOOR_COUNT,
+    )
+
+    # Assert
+    assert result.fabric_heat_loss_w_per_k == pytest.approx(
+        _w000474.LINE_33_FABRIC_HEAT_LOSS_W_PER_K, abs=0.1
+    )
+    assert result.total_w_per_k == pytest.approx(
+        _w000474.LINE_37_TOTAL_FABRIC_HEAT_LOSS_W_PER_K, abs=0.1
+    )
+
+
 def test_section_3_line_33_and_line_37_match_elmhurst_worksheet_000490() -> None:
     """Full §3 fabric heat loss for Elmhurst U985-0001-000490. Once the
     suspended/exposed floor routes are wired and the cert lodges the