diff --git a/datatypes/epc/domain/mapper.py b/datatypes/epc/domain/mapper.py
index c6ba82a1..542dac15 100644
--- a/datatypes/epc/domain/mapper.py
+++ b/datatypes/epc/domain/mapper.py
@@ -1875,15 +1875,24 @@ def _measurement_value(field: Any) -> float:
 
 
 def _total_floor_area_from_building_parts(building_parts: Any) -> Optional[float]:
-    """Sum per-bp `sap_floor_dimensions[*].total_floor_area` to recover the
-    precise TFA. The GOV.UK EPB API JSON's top-level `total_floor_area`
-    is rounded to the integer (cert 001479: 30.45+30.77+5.37+1.92 = 68.51
-    → lodged 69), but the worksheet computes continuous SAP from the
-    unrounded geometry. `epc.total_floor_area_m2` is read directly by
+    """Sum per-bp `sap_floor_dimensions[*].total_floor_area` (plus each bp's
+    `sap_room_in_roof.floor_area` when present) to recover the precise
+    TFA.
+
+    The GOV.UK EPB API JSON's top-level `total_floor_area` is rounded to
+    the integer (cert 001479: 30.45+30.77+5.37+1.92 = 68.51 → lodged 69),
+    but the worksheet computes continuous SAP from the unrounded
+    geometry. `epc.total_floor_area_m2` is read directly by
     `water_heating_from_cert` to derive occupancy N (Appendix J), which
     drives HW, lighting (Appendix L), and internal-gains kWh — so the
-    rounded scalar shifts SAP by ~+0.0006 on cert 001479. Returns None
-    when no per-bp dims are lodged so callers fall back to the scalar."""
+    rounded scalar shifts SAP by ~+0.0006 on cert 001479. RR floor area
+    is NOT in `sap_floor_dimensions` on the API path (it lives under
+    `sap_room_in_roof.floor_area` per RdSAP §3.9 convention), so cert
+    9501's RR storey (31.8 m²) was previously dropped from the per-bp
+    TFA sum → TFA 81.28 vs worksheet 113.08.
+
+    Returns None when no per-bp dims are lodged so callers fall back to
+    the scalar."""
     if not building_parts:
         return None
     total = 0.0
@@ -1893,6 +1902,10 @@ def _total_floor_area_from_building_parts(building_parts: Any) -> Optional[float
         for fd in floor_dims:
             total += _measurement_value(fd.total_floor_area)
             found = True
+        rir: Any = getattr(bp, "sap_room_in_roof", None)
+        if rir is not None and getattr(rir, "floor_area", None) is not None:
+            total += _measurement_value(rir.floor_area)
+            found = True
     return total if found else None
 
 
diff --git a/domain/sap10_calculator/rdsap/tests/test_golden_fixtures.py b/domain/sap10_calculator/rdsap/tests/test_golden_fixtures.py
index e2637995..edac9197 100644
--- a/domain/sap10_calculator/rdsap/tests/test_golden_fixtures.py
+++ b/domain/sap10_calculator/rdsap/tests/test_golden_fixtures.py
@@ -74,9 +74,9 @@ _EXPECTATIONS: tuple[_GoldenExpectation, ...] = (
     _GoldenExpectation(
         cert_number="0240-0200-5706-2365-8010",
         actual_sap=73,
-        expected_sap_resid=-15,
-        expected_pe_resid_kwh_per_m2=+15.6873,
-        expected_co2_resid_tonnes_per_yr=+0.8999,
+        expected_sap_resid=-14,
+        expected_pe_resid_kwh_per_m2=+12.4941,
+        expected_co2_resid_tonnes_per_yr=+0.6957,
         notes=(
             "Detached house, TFA 118, age J, oil boiler PCDB-listed + PV + "
             "RR on BP[0]. Mapper DOES extract sap_room_in_roof.room_in_roof_"
@@ -135,8 +135,8 @@ _EXPECTATIONS: tuple[_GoldenExpectation, ...] = (
         cert_number="6035-7729-2309-0879-2296",
         actual_sap=70,
         expected_sap_resid=-6,
-        expected_pe_resid_kwh_per_m2=+49.5139,
-        expected_co2_resid_tonnes_per_yr=+1.1423,
+        expected_pe_resid_kwh_per_m2=+48.3043,
+        expected_co2_resid_tonnes_per_yr=+1.1019,
         notes=(
             "Mid-terrace, TFA 128, age A, gas combi Table 4b code 104. "
             "Slice 59 per-bp window apportionment tightens all 3 "