diff --git a/packages/domain/src/domain/sap/rdsap/cert_to_inputs.py b/packages/domain/src/domain/sap/rdsap/cert_to_inputs.py
index c6892866..cd3c3c2b 100644
--- a/packages/domain/src/domain/sap/rdsap/cert_to_inputs.py
+++ b/packages/domain/src/domain/sap/rdsap/cert_to_inputs.py
@@ -52,7 +52,7 @@ from domain.ml.sap_efficiencies import (
     seasonal_efficiency,
     water_heating_efficiency as _legacy_water_heating_efficiency,
 )
-from domain.sap.calculator import CalculatorInputs, WindowInput, _solar_gains_w
+from domain.sap.calculator import CalculatorInputs, WindowInput
 from domain.sap.tables.table_12 import (
     co2_factor_kg_per_kwh,
     primary_energy_factor,
@@ -67,7 +67,7 @@ from domain.sap.worksheet.heat_transmission import (
     DwellingExposure,
     heat_transmission_from_cert,
 )
-from domain.sap.worksheet.solar_gains import Orientation
+from domain.sap.worksheet.solar_gains import Orientation, solar_gains_from_cert
 from domain.sap.worksheet.ventilation import (
     MechanicalVentilationKind,
     ventilation_from_inputs,
@@ -998,18 +998,16 @@ def cert_to_inputs(
         # SAP10.2 line (73)m — total internal gains W/month from §5
         # orchestrator (composed above).
         internal_gains_monthly_w=internal_gains_monthly_w,
-        # SAP10.2 line (83)m — total solar gains W/month. Computed here via
-        # the legacy `_solar_gains_w` per-month leaf to preserve identical
-        # behaviour during the §6 wiring migration; the next slice swaps
-        # this for the §6 orchestrator `solar_gains_from_cert`.
-        solar_gains_monthly_w=tuple(
-            _solar_gains_w(
-                windows=_window_inputs(epc.sap_windows),
-                region=_region_index(epc.region_code),
-                month=m,
-            )
-            for m in range(1, 13)
-        ),
+        # SAP10.2 line (83)m — total solar gains W/month via §6 orchestrator.
+        # Cert summaries don't lodge roof windows or rooflights distinctly
+        # (Elmhurst data shows them all as `window_location = External wall`);
+        # both pass-throughs are empty. Per-fixture §6 conformance is
+        # exercised separately in `test_solar_gains.py`.
+        solar_gains_monthly_w=solar_gains_from_cert(
+            epc=epc,
+            region=_region_index(epc.region_code),
+            overshading=_INTERNAL_GAINS_DEFAULT_OVERSHADING,
+        ).total_solar_gains_monthly_w,
         region=_region_index(epc.region_code),
         windows=_window_inputs(epc.sap_windows),
         control_type=_control_type(main),