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 82f344c1..0517fb54 100644
--- a/packages/domain/src/domain/sap/rdsap/cert_to_inputs.py
+++ b/packages/domain/src/domain/sap/rdsap/cert_to_inputs.py
@@ -125,6 +125,18 @@ _DEFAULT_THERMAL_MASS_PARAMETER_KJ_PER_M2_K: Final[float] = 250.0
 _DEFAULT_PUMPS_FANS_KWH_PER_YR: Final[float] = 130.0
 
 
+# SAP 10.3 Table 9 main_heating_control codes → control type (1/2/3).
+# Type 1: no time + temp control, or one but not both.
+# Type 2: programmer + room thermostat (+/− TRVs).
+# Type 3: time-and-temperature zone control (e.g. separate living-zone
+# programmer + thermostat).
+_CONTROL_TYPE_BY_CODE: Final[dict[int, int]] = {
+    2101: 1, 2102: 1, 2103: 1, 2104: 1,
+    2105: 2, 2106: 2, 2107: 2, 2108: 2, 2109: 2,
+    2110: 3, 2111: 3, 2112: 3, 2113: 3,
+}
+
+
 # SAP 10.2 Table 4a "electric heating" range that picks up an Economy-7
 # off-peak tariff for the space-heating fuel cost: electric storage
 # heaters (401-409), high-heat-retention storage heaters (421-425), and
@@ -254,9 +266,15 @@ def _first_main_heating(epc: EpcPropertyData) -> Optional[MainHeatingDetail]:
 
 
 def _control_type(main: Optional[MainHeatingDetail]) -> int:
-    """SAP 10.3 §7.1 / Table 9 control type 1/2/3. Defaults to 2
-    (programmer + room thermostat or better) — the modal RdSAP case."""
-    _ = main  # cert-side heating-control code map is Session B work
+    """SAP 10.3 §7.1 / Table 9 control type 1/2/3 from the
+    `main_heating_control` code on `MainHeatingDetail`. Defaults to 2
+    (programmer + room thermostat) when the code is missing — the modal
+    RdSAP case."""
+    if main is None:
+        return 2
+    code = main.main_heating_control
+    if isinstance(code, int) and code in _CONTROL_TYPE_BY_CODE:
+        return _CONTROL_TYPE_BY_CODE[code]
     return 2
 
 
@@ -302,6 +320,8 @@ def _space_heating_fuel_cost_gbp_per_kwh(main: Optional[MainHeatingDetail]) -> f
     return _fuel_cost_gbp_per_kwh(main)
 
 
+
+
 def _co2_factor_kg_per_kwh(main: Optional[MainHeatingDetail]) -> float:
     """SAP 10.3 Table 12 CO2 emission factor by Table 32 fuel code."""
     code = _main_fuel_code(main)
@@ -382,12 +402,12 @@ def cert_to_inputs(epc: EpcPropertyData) -> CalculatorInputs:
     main_code = main.sap_main_heating_code if main is not None else None
     main_category = main.main_heating_category if main is not None else None
     main_fuel = _main_fuel_code(main)
-
-    eff = seasonal_efficiency(main_code, main_category, main_fuel)
-    water_eff = water_heating_efficiency(epc.sap_heating.water_heating_code, main_code)
     primary_age = (
         epc.sap_building_parts[0].construction_age_band if epc.sap_building_parts else None
     )
+
+    eff = seasonal_efficiency(main_code, main_category, main_fuel)
+    water_eff = water_heating_efficiency(epc.sap_heating.water_heating_code, main_code)
     hw_kwh = predicted_hot_water_kwh(
         total_floor_area_m2=epc.total_floor_area_m2,
         seasonal_efficiency_water=water_eff,
diff --git a/packages/domain/src/domain/sap/rdsap/tests/test_cert_to_inputs.py b/packages/domain/src/domain/sap/rdsap/tests/test_cert_to_inputs.py
index ec854d31..112f73bd 100644
--- a/packages/domain/src/domain/sap/rdsap/tests/test_cert_to_inputs.py
+++ b/packages/domain/src/domain/sap/rdsap/tests/test_cert_to_inputs.py
@@ -218,6 +218,41 @@ def test_mains_gas_fuel_cost_in_gbp_per_kwh() -> None:
     assert inputs.other_fuel_cost_gbp_per_kwh == 0.0348
 
 
+def test_main_heating_control_code_maps_to_sap_control_type() -> None:
+    # Arrange — Table 9 control type derives from the main_heating_control
+    # field. 2103 (room thermostat only, no programmer) → type 1; 2106
+    # (programmer + room thermostat + TRVs) → type 2; 2110 (zone control)
+    # → type 3.
+    def _epc_with_control(code: int):
+        return make_minimal_sap10_epc(
+            total_floor_area_m2=_TYPICAL_TFA_M2,
+            habitable_rooms_count=4,
+            region_code="1",
+            sap_building_parts=[make_building_part(
+                floor_dimensions=[make_floor_dimension(total_floor_area_m2=90.0, floor=0)],
+            )],
+            sap_heating=make_sap_heating(
+                main_heating_details=[
+                    MainHeatingDetail(
+                        has_fghrs=False, main_fuel_type=26, heat_emitter_type=1,
+                        emitter_temperature=1, main_heating_control=code,
+                        main_heating_category=2, sap_main_heating_code=102,
+                    ),
+                ],
+            ),
+        )
+
+    # Act
+    type_1 = cert_to_inputs(_epc_with_control(2103))
+    type_2 = cert_to_inputs(_epc_with_control(2106))
+    type_3 = cert_to_inputs(_epc_with_control(2110))
+
+    # Assert
+    assert type_1.control_type == 1
+    assert type_2.control_type == 2
+    assert type_3.control_type == 3
+
+
 def test_electric_storage_heater_space_heating_at_off_peak_rate() -> None:
     # Arrange — RdSAP convention: when the main heating is electric-
     # storage (code 401-409) or direct-electric (191-196), space heating
diff --git a/packages/domain/src/domain/sap/worksheet/heat_transmission.py b/packages/domain/src/domain/sap/worksheet/heat_transmission.py
index 3c63c9ca..21302886 100644
--- a/packages/domain/src/domain/sap/worksheet/heat_transmission.py
+++ b/packages/domain/src/domain/sap/worksheet/heat_transmission.py
@@ -79,6 +79,12 @@ def _int_or_none(value: Any) -> Optional[int]:
 
 
 def _parse_thickness_mm(value: Any) -> Optional[int]:
+    """Parse a `wall_insulation_thickness` (or roof/floor) field. "NI" in
+    the RdSAP cert is treated as 0 mm: parity-tested on the 100-cert
+    sample, switching to None (cascade-50mm-default-for-present) over-
+    corrected because many "NI" certs are genuinely uninsulated. This
+    will be revisited once the cascade learns to use wall_insulation_type
+    as a stronger signal (Session B follow-up)."""
     if value is None:
         return None
     if isinstance(value, int):