diff --git a/.claude/settings.json b/.claude/settings.json
deleted file mode 100644
index f9ab3156..00000000
--- a/.claude/settings.json
+++ /dev/null
@@ -1,168 +0,0 @@
-{
-  "permissions": {
-    "allow": [
-      "Bash(python -c ' *)",
-      "Bash(python -m pytest tests/ -v --no-cov)",
-      "Bash(git -C /workspaces/model diff --stat)",
-      "Bash(python -c \"import moto; print\\('moto installed:', moto.__version__\\)\")",
-      "Bash(grep -E \"\\\\.\\(py|sql\\)$\")",
-      "Bash(xargs basename -a)",
-      "Bash(ls -la /workspaces/home 2>/dev/null | head -20)",
-      "Read(//workspaces/home/**)",
-      "Bash(command -v uv)",
-      "Bash(uv --version)",
-      "Bash(echo \"uv: $\\(uv --version\\)\")",
-      "Bash(python -m pyright --version)",
-      "Bash(npx --no-install pyright --version)",
-      "Bash(node /home/vscode/.npm/_npx/110e52990071af13/node_modules/pyright/dist/pyright.js --outputjson etl/hubspot/hubspotClient.py etl/hubspot/hubspotDataTodB.py etl/hubspot/project_data.py etl/hubspot/scripts/scraper/main.py backend/app/db/models/hubspot_project_data.py backend/app/db/models/hubspot_deal_data.py etl/hubspot/tests/test_scraper_handler.py etl/hubspot/tests/test_hubspot_data_to_db.py etl/hubspot/tests/test_hubspot_client_integration.py)",
-      "Bash(python -c \"import sys,json; d=json.load\\(sys.stdin\\); s=d['summary']; print\\('errors',s['errorCount'],'warnings',s['warningCount']\\); [print\\(f\\\\\"{x['severity']}: {x['file'].split\\('/'\\)[-1]}:{x['range']['start']['line']+1} {x['rule'] if 'rule' in x else ''} -- {x['message'].splitlines\\(\\)[0]}\\\\\"\\) for x in d['generalDiagnostics'] if x['severity']=='error']\")",
-      "Bash(node /home/vscode/.npm/_npx/110e52990071af13/node_modules/pyright/dist/pyright.js etl/hubspot/project_data.py backend/app/db/models/hubspot_project_data.py)",
-      "Bash(python -c \"import sqlmodel, sqlalchemy, hubspot; print\\('deps importable'\\)\")",
-      "Bash(python -m pytest --version)",
-      "Bash(python -m pytest etl/hubspot/tests/ -m \"not integration\" -p no:cacheprovider -o addopts=\"\" -q)",
-      "Bash(node /home/vscode/.npm/_npx/110e52990071af13/node_modules/pyright/dist/pyright.js --pythonpath /usr/local/bin/python etl/hubspot/project_data.py backend/app/db/models/hubspot_project_data.py)",
-      "Bash(node /home/vscode/.npm/_npx/110e52990071af13/node_modules/pyright/dist/pyright.js --pythonpath /usr/local/bin/python etl/hubspot/company_data.py)",
-      "Bash(python /tmp/inspect_project.py)",
-      "Read(//home/vscode/github/**)",
-      "Bash(find / -maxdepth 6 -type d -name assessment-model)",
-      "Bash(terraform fmt *)",
-      "Bash(terraform init *)",
-      "Bash(terraform validate *)",
-      "Bash(python -m pytest tests/orchestration/test_landlord_description_overrides_orchestrator.py -q)",
-      "Bash(python -m pytest tests/orchestration/test_landlord_description_overrides_orchestrator.py tests/repositories/landlord_overrides -q --no-cov)",
-      "Bash(python -m py_compile tests/infrastructure/chatgpt/test_chatgpt_column_classifier.py)",
-      "Bash(git add *)",
-      "Bash(git status *)",
-      "Bash(cp pyrightconfig.json /tmp/pyrightconfig.bak.json)",
-      "Bash(python3 -)",
-      "Bash(npx --yes pyright infrastructure/postgres/landlord_overrides_postgres_repository.py applications/landlord_description_overrides/handler.py tests/repositories/landlord_overrides/postgres/test_landlord_overrides_postgres_repository.py orchestration/classifiable_column.py)",
-      "Bash(git stash *)",
-      "Bash(npx --yes pyright applications/landlord_description_overrides/handler.py)",
-      "Bash(python3 -m pytest tests/repositories/landlord_overrides/postgres/test_landlord_overrides_postgres_repository.py -q)",
-      "Bash(python3 -m pytest tests/orchestration/test_landlord_description_overrides_orchestrator.py tests/repositories/landlord_overrides/ -q -p no:cov)",
-      "Bash(python3 -m pytest tests/orchestration/test_landlord_description_overrides_orchestrator.py tests/repositories/landlord_overrides/ -q)",
-      "Bash(cp pyrightconfig.json /tmp/pyrightconfig.bak2.json)",
-      "Bash(npx --yes pyright infrastructure/landlord_overrides/landlord_overrides_postgres_repository.py tests/repositories/landlord_overrides/postgres/test_landlord_overrides_postgres_repository.py)",
-      "Bash(GIT_EDITOR=true git rebase --continue)",
-      "Bash(git worktree *)",
-      "Bash(git branch *)",
-      "Bash(echo \"exit: $?\")",
-      "Bash(git reset *)",
-      "Bash(echo \"fetch-exit: $?\")",
-      "Bash(sed -n *)",
-      "Bash(set -e)",
-      "Bash(git rm *)",
-      "Bash(git ls-tree *)",
-      "Bash(command -v pyright)",
-      "Bash(git merge *)",
-      "Bash(git rev-list *)",
-      "Bash(git remote *)",
-      "Bash(git ls-remote *)",
-      "Bash(grep -v '\\\\.sample$')",
-      "Bash([ -f \".git/hooks/$h\" ])",
-      "Bash(python3 -m pytest tests/test_lambda_packaging.py -p no:cacheprovider --no-header -q)",
-      "Bash(python3 -m pytest tests/test_lambda_packaging.py -p no:cov --no-header -q)",
-      "Bash(python3 -m pytest tests/test_lambda_packaging.py --no-cov -p no:cacheprovider -q)",
-      "Bash(python3 -m pytest tests/test_lambda_packaging.py --no-cov -q)",
-      "Bash(python3 -m pyright tests/test_lambda_packaging.py)",
-      "Bash(python3 -m pytest tests/ --collect-only --no-cov -q)",
-      "Bash(python3 -c \"import yaml; [print\\(f, 'OK'\\) for f in ['.github/workflows/ddd_tests.yml','.github/workflows/unit_tests.yml'] if yaml.safe_load\\(open\\(f\\)\\)]\")",
-      "Bash(python3 -m pytest tests/ -q --no-cov)",
-      "Bash(python3 -c ' *)",
-      "Bash(python3 -m pyright --outputjson scripts/hyde/main.py)",
-      "Bash(python3 -c \"import json,sys; d=json.load\\(sys.stdin\\); s=d['summary']; print\\('errors:',s['errorCount'],'warnings:',s['warningCount']\\); [print\\(f\\\\\"  L{e['range']['start']['line']+1}: {e['message'].splitlines\\(\\)[0]}\\\\\"\\) for e in d['generalDiagnostics'] if e['severity']=='error']\")",
-      "Bash(python3 -c \"import json,sys; d=json.load\\(sys.stdin\\); s=d['summary']; print\\('pyright errors:',s['errorCount'],'warnings:',s['warningCount']\\); [print\\(f\\\\\"  L{e['range']['start']['line']+1}: {e['message'].splitlines\\(\\)[0]}\\\\\"\\) for e in d['generalDiagnostics'] if e['severity']=='error']\")",
-      "Bash(python3 main.py)",
-      "Bash(netstat -ltnp)",
-      "Bash(fuser 8000/tcp)",
-      "Bash(kill 351610 685390 351625)",
-      "Read(//proc/531213/net/**)",
-      "Bash(ps -p 351610 -o pid=)",
-      "Bash(python -)",
-      "Bash(python -m pytest \"datatypes/epc/domain/tests/test_from_rdsap_schema.py::TestRdSap20_0_0ReducedFieldSynthesis::test_cert_omitting_sap_windows_maps_without_missing_required_field\")",
-      "Bash(python -m pytest datatypes/epc/domain/tests/test_from_rdsap_schema.py infrastructure/epc_client/tests/test_mapper_corpus.py)",
-      "Bash(git -C /workspaces/model stash push -u -- datatypes/epc/schema/rdsap_schema_20_0_0.py datatypes/epc/domain/mapper.py datatypes/epc/domain/tests/test_from_rdsap_schema.py)",
-      "Bash(python -m pytest \"datatypes/epc/domain/tests/test_from_rdsap_schema.py::TestFromRdSapSchema21_0_1::test_total_floor_area\")",
-      "Bash(git -C /workspaces/model stash pop)",
-      "Bash(python -m pytest \"datatypes/epc/domain/tests/test_from_rdsap_schema.py::TestRdSap20_0_0ReducedFieldSynthesis::test_band_more_than_typical_scales_glazing_by_1_25\")",
-      "Bash(python -m pytest \"datatypes/epc/domain/tests/test_from_rdsap_schema.py::TestRdSap20_0_0ReducedFieldSynthesis\")",
-      "Bash(python -m pytest \"datatypes/epc/domain/tests/test_from_rdsap_schema.py::TestRdSap20_0_0ReducedFieldSynthesis::test_synthesised_glazing_type_routed_through_cascade\")",
-      "Bash(python -m pytest infrastructure/epc_client/tests/test_mapper_corpus.py -k \"wip_schema_20\" -q -p no:cov --no-header -rN)",
-      "Bash(python -m pytest infrastructure/epc_client/tests/test_mapper_corpus.py -k \"wip_schema_20\" -q --no-header)",
-      "Bash(timeout 150 python scripts/eon/find_epc_data.py)",
-      "Bash(python -m scripts.run_modelling_e2e --scenario-id 1266 --portfolio-id 785 --measures high_heat_retention_storage_heaters,solar_pv 709634 709635 709636 709638 709639 709640 709641 709642 709644)",
-      "Read(//home/vscode/.claude/skills/grill-me/**)",
-      "Bash(awk '{print $9, $5}')",
-      "Bash(grep -E \"\\\\.py$\")",
-      "Bash(python3 scripts/eon/harvest_certs.py)",
-      "Bash(python scripts/eon/harvest_certs.py)",
-      "Bash(git commit -q -m ' *)",
-      "Bash(timeout 250 npx -y pyright@1.1.410 datatypes/epc/domain/mapper.py)",
-      "Bash(git check-ignore *)",
-      "Bash(timeout 250 npx -y pyright@1.1.410 datatypes/epc/schema/rdsap_schema_18_0.py datatypes/epc/domain/mapper.py)",
-      "Bash(timeout 250 npx -y pyright@1.1.410 datatypes/epc/schema/rdsap_schema_17_1.py datatypes/epc/domain/mapper.py)",
-      "Bash(python -m scripts.run_modelling_e2e --scenario-id 1266 --portfolio-id 785 --measures high_heat_retention_storage_heaters,solar_pv 709634 709635 709636 709638 709639 709640 709641 709642 709643 709644 709645 709637)",
-      "Read(//workspaces/**)",
-      "Bash(python -m scripts.run_modelling_e2e --scenario-id 1266 --portfolio-id 785 --measures high_heat_retention_storage_heaters,solar_pv 709634)",
-      "Bash(python 2_export_data.py)",
-      "Bash(git commit -q -m 'Map RdSAP-Schema-17.0 certs to EpcPropertyData 🟥 *)",
-      "Bash(python -m py_compile tests/utilities/floats.py backend/app/db/functions/tests/test_portfolio_functions.py backend/documents_parser/tests/test_summary_pdf_mapper_chain.py backend/documents_parser/tests/test_heating_systems_corpus.py)",
-      "Bash(PYTHONPATH=/workspaces/model python -)",
-      "Bash(npx --no-install pyright datatypes/epc/schema/sap_schema_17_1.py datatypes/epc/domain/mapper.py datatypes/epc/domain/tests/test_from_sap_schema.py)",
-      "Bash(git commit -q -m 'Map full-SAP cert identity and scalar fields to EpcPropertyData 🟩 *)",
-      "Bash(npx --no-install pyright --outputjson datatypes/epc/domain/mapper.py)",
-      "Bash(git commit -q -m 'Carry full-SAP measured fabric U-value descriptions into the domain model 🟩 *)",
-      "Bash(python scripts/hyde/elmhurst_session.py --help)",
-      "Bash(python scripts/hyde/elmhurst_session.py status)",
-      "Bash(DISPLAY=:99 import -window root /tmp/hyde-viewer/elm_now2.png)",
-      "Bash(DISPLAY=:99 timeout 90 python scripts/hyde/elmhurst_explore.py \"https://rdsap10online.elmhurstenergy.co.uk/Processing/WebFormAddress.aspx?Guid=B44A0DB4-4C08-4241-B818-86F060172105&Referrer=https%3a%2f%2fmembers.elmhurstenergy.co.uk%2fRdsapZone%2fHome.aspx\")",
-      "Bash(DISPLAY=:99 timeout 90 python scripts/hyde/elmhurst_explore.py \"https://rdsap10online.elmhurstenergy.co.uk/Processing/WebFormPropertyDescription.aspx?Guid=B44A0DB4-4C08-4241-B818-86F060172105\")",
-      "Bash(DISPLAY=:99 timeout 90 python scripts/hyde/elmhurst_explore.py \"https://rdsap10online.elmhurstenergy.co.uk/Processing/WebFormAddress.aspx?Guid=B44A0DB4-4C08-4241-B818-86F060172105\")",
-      "Bash(DISPLAY=:99 timeout 150 python scripts/hyde/elmhurst_fill.py)",
-      "Bash(pkill -f \"rdsap10\\\\|for-testing\")",
-      "Bash(rm -f scripts/hyde/.elmhurst-session/Singleton*)",
-      "Bash(DISPLAY=:99 timeout 280 python -u scripts/hyde/elmhurst_fill.py --page property_description --commit)",
-      "Bash(npx --no-install pyright scripts/hyde/elmhurst_download.py)",
-      "Edit(/.claude/skills/expand-sap-accuracy-corpus/**)",
-      "Bash(PYTHONPATH=/workspaces/model python scripts/fetch_real_life_epc_sample.py 10093116528)",
-      "Bash(PYTHONPATH=/workspaces/model python -c ' *)",
-      "Bash(bash scripts/hyde/start_viewer.sh)",
-      "Bash(DISPLAY=:99 ELMHURST_URL=\"https://rdsap10online.elmhurstenergy.co.uk/Processing/WebFormAddress.aspx?Guid=B44A0DB4-4C08-4241-B818-86F060172105\" python scripts/hyde/elmhurst_session.py login)",
-      "Bash(break)",
-      "Bash(DISPLAY=:99 timeout 90 python /tmp/check_session.py)",
-      "Bash(pkill -9 -f \"elm_login_hold.py\")",
-      "Bash(pkill -9 -f \"elmhurst-session\")",
-      "Bash(ELM_ACCESS=\"P960-0001\" ELM_PWD=\"y22bseGUzr\" DISPLAY=:99 timeout 150 python /tmp/elm_build_dims.py)",
-      "Bash(ELM_ACCESS=\"P960-0001\" ELM_PWD=\"y22bseGUzr\" DISPLAY=:99 timeout 120 python /tmp/elm_dump_full.py Walls WebFormWalls.aspx)",
-      "Bash(ELM_ACCESS=\"P960-0001\" ELM_PWD=\"y22bseGUzr\" DISPLAY=:99 timeout 120 python /tmp/elm_walls_disc.py)",
-      "Bash(ELM_ACCESS=\"P960-0001\" ELM_PWD=\"y22bseGUzr\" DISPLAY=:99 timeout 120 python /tmp/elm_roof_disc.py)",
-      "Bash(ELM_ACCESS=\"P960-0001\" ELM_PWD=\"y22bseGUzr\" DISPLAY=:99 timeout 120 python /tmp/elm_dump_full.py Openings WebFormOpenings.aspx)",
-      "Bash(ELM_ACCESS=\"P960-0001\" ELM_PWD=\"y22bseGUzr\" DISPLAY=:99 timeout 120 python /tmp/elm_win_probe.py)",
-      "Bash(ELM_ACCESS=\"P960-0001\" ELM_PWD=\"y22bseGUzr\" DISPLAY=:99 timeout 220 python /tmp/elm_build_openings.py)",
-      "Bash(ELM_ACCESS=\"P960-0001\" ELM_PWD=\"y22bseGUzr\" DISPLAY=:99 timeout 120 python /tmp/elm_tab_probe.py)",
-      "Bash(ELM_ACCESS=\"P960-0001\" ELM_PWD=\"y22bseGUzr\" DISPLAY=:99 timeout 120 python /tmp/elm_del_probe.py)",
-      "Bash(npx --no-install pyright datatypes/epc/domain/epc_property_data.py datatypes/epc/domain/mapper.py domain/sap10_calculator/rdsap/cert_to_inputs.py)",
-      "Bash(PYTHONPATH=/workspaces/model python -m pytest domain/sap10_calculator/tests/test_sap_accuracy_corpus.py -q --no-cov)",
-      "Bash(PYTHONPATH=/workspaces/model python -m pytest tests/domain/sap10_calculator/test_real_cert_sap_accuracy.py -q --no-cov)",
-      "Edit(/.claude/skills/epc-to-elmhurst-rdsap-inputs/**)",
-      "Bash(python3 -c \"import sys; sys.path.insert\\(0,'scripts/hyde'\\); import elmhurst_lib; print\\('elmhurst_lib imports OK:', [f for f in dir\\(elmhurst_lib\\) if not f.startswith\\('_'\\)][:12]\\)\")",
-      "Bash(PYTHONPATH=/workspaces/model python -m pytest tests/domain/sap10_calculator/test_real_cert_sap_accuracy.py tests/infrastructure/epc_client/test_sap_accuracy_corpus.py -q --no-cov)",
-      "Bash(PYTHONPATH=/workspaces/model python scripts/fetch_real_life_epc_sample.py 10093116543)",
-      "Bash(echo \"---EXIT $?---\")",
-      "Bash(sudo apt-get update -o Dir::Etc::sourceparts=-)",
-      "Bash(apt-cache policy *)",
-      "Bash(sudo apt-get update)",
-      "Bash(bash scripts/hyde/start_viewer.sh restart)",
-      "Bash(echo \"=== listen sockets \\(port 6080 / 5900\\) ===\"; ss -ltnp 2>/dev/null | grep -E ':6080|:5900' || netstat -ltnp 2>/dev/null | grep -E ':6080|:5900' || echo \"ss/netstat unavailable\" *)",
-      "Read(//proc/5476/**)",
-      "Bash(sudo python -m playwright install-deps chromium)",
-      "Bash(python -m playwright install chromium)",
-      "Bash(python -m playwright --version)",
-      "Bash(pip show *)"
-    ],
-    "additionalDirectories": [
-      "/tmp",
-      "/workspaces/model/scripts/hyde/.elmhurst-session"
-    ]
-  }
-}
diff --git a/.gitignore b/.gitignore
index 9cb34cb3..9c77b311 100644
--- a/.gitignore
+++ b/.gitignore
@@ -304,6 +304,7 @@ backlog/*
 # Local Claude config files
 .claude/*modelling_cohort.csv
 .claude/settings.local.json
+.claude/settings.json
 
 # Local EPC debug cache (scripts/eon)
 scripts/eon/epc_cache.pkl
diff --git a/backend/documents_parser/tests/fixtures/Summary_001431_case45.pdf b/backend/documents_parser/tests/fixtures/Summary_001431_case45.pdf
new file mode 100644
index 00000000..48a5273e
Binary files /dev/null and b/backend/documents_parser/tests/fixtures/Summary_001431_case45.pdf differ
diff --git a/domain/sap10_calculator/calculator.py b/domain/sap10_calculator/calculator.py
index f7099f18..11cecf73 100644
--- a/domain/sap10_calculator/calculator.py
+++ b/domain/sap10_calculator/calculator.py
@@ -42,7 +42,7 @@ Appendix L + U. RdSAP10 Table 32 (p.95) for fuel prices/CO2/PE factors.
 from __future__ import annotations
 
 from abc import ABC, abstractmethod
-from dataclasses import dataclass, field
+from dataclasses import dataclass, field, replace
 from typing import Final, Optional, TYPE_CHECKING
 
 from domain.sap10_calculator.climate.appendix_u import external_temperature_c
@@ -863,6 +863,25 @@ class Sap10Calculator(SapCalculator):
     """
 
     def calculate(self, epc: "EpcPropertyData") -> SapResult:
-        from domain.sap10_calculator.rdsap.cert_to_inputs import cert_to_inputs
+        # SAP 10.2 Appendix U paragraph 1 (p.124): the SAP and EI ratings are
+        # computed on UK-average climate (so ratings are nationally
+        # comparable), but "other calculations (such as for energy use and
+        # costs on EPCs) are done using local weather" — the EPC-displayed
+        # CO2 emissions and primary energy use postcode-district weather from
+        # the PCDB. So we run two climate cascades and graft the demand
+        # cascade's CO2/PE onto the rating cascade's SAP result. (Worked
+        # example: simulated case 45 — rating SAP 60.53/CO2 692.13 on
+        # UK-average; demand CO2 626.78/PE 6581.59 on the W6 postcode.)
+        from domain.sap10_calculator.rdsap.cert_to_inputs import (
+            cert_to_demand_inputs,
+            cert_to_inputs,
+        )
 
-        return calculate_sap_from_inputs(cert_to_inputs(epc))
+        rating = calculate_sap_from_inputs(cert_to_inputs(epc))
+        demand = calculate_sap_from_inputs(cert_to_demand_inputs(epc))
+        return replace(
+            rating,
+            co2_kg_per_yr=demand.co2_kg_per_yr,
+            primary_energy_kwh_per_yr=demand.primary_energy_kwh_per_yr,
+            primary_energy_kwh_per_m2=demand.primary_energy_kwh_per_m2,
+        )
diff --git a/domain/sap10_calculator/rdsap/cert_to_inputs.py b/domain/sap10_calculator/rdsap/cert_to_inputs.py
index 60da4ce1..cd146109 100644
--- a/domain/sap10_calculator/rdsap/cert_to_inputs.py
+++ b/domain/sap10_calculator/rdsap/cert_to_inputs.py
@@ -2772,7 +2772,11 @@ def _secondary_fuel_cost_gbp_per_kwh(
         meter_type, fuel_is_electric=True
     ):
         return _secondary_off_peak_rate_gbp_per_kwh(meter_type)
-    return prices.unit_price_p_per_kwh(sec_fuel) * _PENCE_TO_GBP
+    # Normalise colliding gov-API enum codes (e.g. 9 dual fuel, whose
+    # value collides with Table-32 9 = LPG SC11F) before the price lookup,
+    # exactly as the main-fuel boundary does — otherwise the same-value
+    # Table lookup mis-prices the secondary at the colliding fuel's rate.
+    return prices.unit_price_p_per_kwh(canonical_fuel_code(sec_fuel)) * _PENCE_TO_GBP
 
 
 def _pv_array_generation_kwh_per_yr(
@@ -3927,6 +3931,10 @@ def _secondary_fuel_code(epc: EpcPropertyData) -> int:
     code = _int_or_none(epc.sap_heating.secondary_fuel_type)
     if code is None:
         return _STANDARD_ELECTRICITY_FUEL_CODE
+    # Normalise colliding gov-API enum codes (e.g. 9 dual fuel, whose value
+    # collides with the LPG Table code) so the CO2/PE factor lookups resolve
+    # to the lodged fuel — mirrors the main-fuel boundary + the cost side.
+    code = canonical_fuel_code(code) or code
     if code in CO2_KG_PER_KWH:
         return code
     return _table_12_factor_fuel_code(code)
@@ -7218,7 +7226,21 @@ def cert_to_inputs(
         epc=epc,
     )
     if apm_efficiencies is not None:
-        eff, water_eff = apm_efficiencies
+        # η_space (N3.6) always replaces the Table 4a default — the heat
+        # pump is the space main. η_water (N3.7a) applies ONLY when the DHW
+        # is actually heated by that main (WHC "from main": 901/902/914). A
+        # separate electric immersion (WHC 903) or other independent DHW
+        # source keeps its own water efficiency (immersion = 100%), not the
+        # HP's water SCOP — otherwise a HP-space + immersion-DHW dwelling
+        # under-counts its hot-water fuel (case 45: water 2130 -> 1894 kWh,
+        # +1.5 SAP, because 187.5% × 0.6 in-use = 112.5% was applied where
+        # the worksheet (216) uses 100%).
+        eff, apm_water_eff = apm_efficiencies
+        if (
+            epc.sap_heating.water_heating_code
+            in _WATER_INHERIT_FROM_MAIN_CODES
+        ):
+            water_eff = apm_water_eff
     if (
         _is_heat_network_main(main)
         and epc.sap_heating.water_heating_code in _WATER_INHERIT_FROM_MAIN_CODES
diff --git a/domain/sap10_calculator/tables/table_32.py b/domain/sap10_calculator/tables/table_32.py
index 8377fe86..14544aea 100644
--- a/domain/sap10_calculator/tables/table_32.py
+++ b/domain/sap10_calculator/tables/table_32.py
@@ -121,11 +121,17 @@ API_FUEL_TO_TABLE_32: Final[dict[int, int]] = {
 #   33 = coal — Table-32 code 33 is the electricity 10-hour low rate
 #        7.5 p vs house coal 3.67 p (and `is_electric_fuel_code(33)`
 #        wrongly classified the coal main as electric).
-# DEFERRED (not included): API 9 = dual fuel (mineral + wood) is also a
-# collision (Table-32 9 = LPG SC11F 3.48 p vs dual fuel 3.99 p) but the
-# 0.45 p delta nets neutral-to-negative on the (outlier-dominated)
-# dual-fuel certs and shifts them in a direction not yet understood —
-# investigate separately.
+#   9  = dual fuel (mineral + wood) — Table-32 code 9 is LPG SC11F
+#        3.48 p vs dual fuel 3.99 p. The gov-API lodges API enum 9 for a
+#        dual-fuel appliance (description "Room heaters, dual fuel
+#        (mineral and wood)"), but the same-value Table-32 lookup returns
+#        LPG 3.48 p, under-pricing the (mostly secondary) dual-fuel heat.
+#        A prior session deferred this as "direction not understood"
+#        while the EPC PE/CO2 lens was confounded by the climate-cascade
+#        bug (fixed in fc7c4d2d); on the corrected lens the dual-fuel
+#        secondary cohort over-rates (SAP too high = cost too low) by
+#        +0.55 signed, and pricing UP to the dual-fuel 3.99 p row reduces
+#        that over-rate — the correct direction.
 #
 # COMMUNITY FUELS (handled elsewhere, NOT here): API 30 (waste
 # combustion), 31 (biomass) and 32 (biogas) — all "(community)" in the
@@ -140,7 +146,7 @@ API_FUEL_TO_TABLE_32: Final[dict[int, int]] = {
 # cert_to_inputs), where the community meaning is unambiguous. Community
 # fuels 20/25 do not collide with an electricity code, so they resolve
 # correctly through the heat-network path without any special handling.
-_GOV_API_COLLISION_FUELS: Final[frozenset[int]] = frozenset({5, 33})
+_GOV_API_COLLISION_FUELS: Final[frozenset[int]] = frozenset({5, 9, 33})
 
 
 def canonical_fuel_code(fuel_code: Optional[int]) -> Optional[int]:
diff --git a/domain/sap10_calculator/worksheet/heat_transmission.py b/domain/sap10_calculator/worksheet/heat_transmission.py
index 0fed5174..80c65aac 100644
--- a/domain/sap10_calculator/worksheet/heat_transmission.py
+++ b/domain/sap10_calculator/worksheet/heat_transmission.py
@@ -1166,6 +1166,16 @@ def heat_transmission_from_cert(
         # lodgement is authoritative. Mirrors the roof's "another dwelling
         # above" override above. Cert 2115-4121-4711-9361-3686.
         part_floor_is_party = "another dwelling below" in (part.floor_type or "").lower()
+        # A part whose floor_type is a GROUND floor sits in contact with the
+        # ground (RdSAP 10 §3.12) and is therefore a heat-loss floor, even when
+        # the dwelling-level flat heuristic (`_dwelling_exposure`) defaults a
+        # flat to has_exposed_floor=False. The Elmhurst Summary path lodges a
+        # ground-floor flat's position as a "Ground floor" floor_type (not the
+        # API floor_heat_loss=1 exposed code), so without this signal the
+        # cascade dropped its ground floor entirely — simulated case 45 (a
+        # ground-floor flat the mapper labelled "Top-floor flat"): worksheet
+        # (28a) = 47.0 × 0.54 = 25.38 W/K billed as 0, over-rating by +7 SAP.
+        part_floor_is_ground = "ground floor" in (part.floor_type or "").lower()
         # A floor lodged as a heat-loss floor — *exposed* (API
         # floor_heat_loss=1 → `is_exposed_floor`, "an exposed floor if there
         # is an open space below") or *above a partially heated space* (API
@@ -1178,6 +1188,7 @@ def heat_transmission_from_cert(
         # the "another dwelling below" party signal overrides it downward.
         part_has_exposed_floor = (
             exposure.has_exposed_floor or is_exposed_floor or is_above_partial
+            or part_floor_is_ground
         ) and not part_floor_is_party
         floor_area_total = _round_half_up(
             geom["ground_floor_area_m2"] if part_has_exposed_floor else 0.0,
diff --git a/scripts/dive_cert.py b/scripts/dive_cert.py
new file mode 100644
index 00000000..8d6da1b4
--- /dev/null
+++ b/scripts/dive_cert.py
@@ -0,0 +1,108 @@
+"""Deep-dive a single corpus cert: lodged vs computed SAP/CO2/PE + the full
+intermediate line-ref dump + the mapped fabric/heat-loss inputs, so the
+diverging line is visible WITHOUT an Elmhurst worksheet.
+
+USAGE
+    PYTHONPATH=/workspaces/model python scripts/dive_cert.py <cert_number_or_substr>
+    PYTHONPATH=/workspaces/model python scripts/dive_cert.py --filter wall_insulation_type=3  [--n 8]
+"""
+from __future__ import annotations
+
+import json
+import sys
+from pathlib import Path
+from typing import Any
+
+from datatypes.epc.domain.mapper import EpcPropertyDataMapper
+from domain.sap10_calculator.calculator import calculate_sap_from_inputs
+from domain.sap10_calculator.rdsap.cert_to_inputs import (
+    SAP_10_2_SPEC_PRICES,
+    cert_to_demand_inputs,
+    cert_to_inputs,
+)
+from scripts.profile_api_error import features
+
+_CORPUS = Path("backend/epc_api/json_samples/RdSAP-Schema-21.0.1/corpus.jsonl")
+
+
+def _cert_id(doc: dict[str, Any]) -> str:
+    return str(
+        doc.get("certificate_number")
+        or doc.get("lmk_key")
+        or doc.get("uprn")
+        or "?"
+    )
+
+
+def _dump(doc: dict[str, Any]) -> None:
+    cert = _cert_id(doc)
+    lodged_sap = doc.get("energy_rating_current")
+    lodged_co2 = doc.get("co2_emissions_current")
+    lodged_pe = doc.get("energy_consumption_current")
+    epc = EpcPropertyDataMapper.from_api_response(doc)
+    r = calculate_sap_from_inputs(cert_to_inputs(epc, prices=SAP_10_2_SPEC_PRICES))
+    # SAP/EI rating is the UK-average rating cascade (`r`); EPC CO2/PE use the
+    # postcode demand cascade (SAP 10.2 Appendix U p.124). Display CO2/PE from
+    # the demand cascade so they compare like-for-like with the lodged EPC.
+    d = calculate_sap_from_inputs(cert_to_demand_inputs(epc, prices=SAP_10_2_SPEC_PRICES))
+    print("=" * 90)
+    print(f"CERT {cert}")
+    print(
+        f"  SAP  lodged={lodged_sap}  ours={r.sap_score_continuous:.2f}  "
+        f"d={r.sap_score_continuous - (lodged_sap or 0):+.2f}"
+    )
+    if lodged_co2 is not None:
+        print(
+            f"  CO2  lodged={lodged_co2:.3f}  ours={d.co2_kg_per_yr / 1000:.3f} t  "
+            f"d={d.co2_kg_per_yr / 1000 - lodged_co2:+.3f}  (demand cascade)"
+        )
+    if lodged_pe is not None:
+        print(
+            f"  PE   lodged={lodged_pe:.1f}  ours={d.primary_energy_kwh_per_m2:.1f}  "
+            f"d={d.primary_energy_kwh_per_m2 - lodged_pe:+.1f} kWh/m2  (demand cascade)"
+        )
+    print(
+        f"  energy kWh/yr: spaceheat={r.space_heating_kwh_per_yr:.0f} "
+        f"main={r.main_heating_fuel_kwh_per_yr:.0f} "
+        f"sec={r.secondary_heating_fuel_kwh_per_yr:.0f} "
+        f"hw={r.hot_water_kwh_per_yr:.0f} light={r.lighting_kwh_per_yr:.0f} "
+        f"pumpfan={r.pumps_fans_kwh_per_yr:.0f}"
+    )
+    d = epc.__dict__
+    print("  --- key mapped inputs ---")
+    f = features(doc)
+    for k in (
+        "property_type", "built_form", "age_band", "main_sap_code",
+        "main_heat_cat", "main_fuel", "has_pcdb_main", "main_data_source",
+        "wall_construction", "wall_insulation_type", "roof_codes",
+        "roof_insulation_thickness", "whc", "water_fuel", "immersion_type",
+        "has_cylinder", "has_secondary", "has_pv", "mains_gas", "n_building_parts",
+    ):
+        print(f"    {k:26s}= {f.get(k)}")
+    print("  --- intermediate line refs ---")
+    inter = r.intermediate or {}
+    for k in sorted(inter):
+        print(f"    {k:34s}= {inter[k]:.4f}")
+
+
+def main() -> None:
+    docs = [json.loads(l) for l in _CORPUS.read_text().splitlines() if l.strip()]
+    if "--filter" in sys.argv:
+        spec = sys.argv[sys.argv.index("--filter") + 1]
+        key, _, val = spec.partition("=")
+        n = int(sys.argv[sys.argv.index("--n") + 1]) if "--n" in sys.argv else 6
+        hits = [d for d in docs if str(features(d).get(key)) == val]
+        print(f"{len(hits)} certs match {spec}; dumping first {n}")
+        for d in hits[:n]:
+            _dump(d)
+        return
+    target = sys.argv[1]
+    for d in docs:
+        if target in _cert_id(d):
+            _dump(d)
+            return
+    print(f"no cert matching {target}")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/scripts/profile_corpus_error.py b/scripts/profile_corpus_error.py
new file mode 100644
index 00000000..6ef2c4e6
--- /dev/null
+++ b/scripts/profile_corpus_error.py
@@ -0,0 +1,226 @@
+"""Profile API-path SAP/CO2/PE error over the COMMITTED corpus (no /tmp cache).
+
+WHAT THIS IS FOR
+----------------
+The accuracy thesis: the gov-API response carries the full SAP input set and our
+calculator is deterministic, so EVERY cert should reproduce the lodged
+SAP/CO2/PE. Any divergence is an input-handling bug, not irreducible noise.
+
+This is the per-cert microscope for that loop. It runs the in-repo corpus
+(``backend/epc_api/json_samples/RdSAP-Schema-21.0.1/corpus.jsonl``) through the
+real ``from_api_response`` -> ``cert_to_inputs`` -> ``calculate_sap_from_inputs``
+path, then:
+  1. buckets the signed SAP error by raw-API feature (reusing
+     ``profile_api_error.features``) ranked by wasted accuracy, so a
+     dropped/mis-mapped field surfaces as a biased bucket;
+  2. for the worst over- and under-raters, prints the PE/CO2-vs-cost split so
+     each can be triaged WITHOUT a worksheet:
+       - PE & CO2 both ~match lodged but SAP off  -> COST-side bug
+         (tariff / PV export / standing charge / secondary fuel);
+       - PE/CO2 also off                          -> DEMAND-side bug
+         (fabric / ventilation / gains / heating demand).
+
+USAGE
+-----
+    PYTHONPATH=/workspaces/model python scripts/profile_corpus_error.py
+    PYTHONPATH=/workspaces/model python scripts/profile_corpus_error.py --min-n 15 --worst 40
+"""
+from __future__ import annotations
+
+import json
+import statistics as stats
+import sys
+from collections import defaultdict
+from pathlib import Path
+from typing import Any, Optional
+
+from datatypes.epc.domain.mapper import EpcPropertyDataMapper
+from domain.sap10_calculator.calculator import calculate_sap_from_inputs
+from domain.sap10_calculator.rdsap.cert_to_inputs import (
+    cert_to_demand_inputs,
+    SAP_10_2_SPEC_PRICES,
+    cert_to_inputs,
+)
+from scripts.profile_api_error import features
+
+_CORPUS = Path("backend/epc_api/json_samples/RdSAP-Schema-21.0.1/corpus.jsonl")
+
+
+class Row:
+    __slots__ = (
+        "cert", "sap_err", "co2_err_t", "pe_err", "lodged_sap",
+        "our_sap", "lodged_pe", "our_pe", "feats",
+    )
+
+    def __init__(
+        self,
+        cert: str,
+        sap_err: float,
+        co2_err_t: Optional[float],
+        pe_err: Optional[float],
+        lodged_sap: float,
+        our_sap: float,
+        lodged_pe: Optional[float],
+        our_pe: float,
+        feats: dict[str, Any],
+    ) -> None:
+        self.cert = cert
+        self.sap_err = sap_err
+        self.co2_err_t = co2_err_t
+        self.pe_err = pe_err
+        self.lodged_sap = lodged_sap
+        self.our_sap = our_sap
+        self.lodged_pe = lodged_pe
+        self.our_pe = our_pe
+        self.feats = feats
+
+
+def _load() -> list[dict[str, Any]]:
+    return [
+        json.loads(line)
+        for line in _CORPUS.read_text().splitlines()
+        if line.strip()
+    ]
+
+
+def _compute(corpus: list[dict[str, Any]]) -> tuple[list[Row], int, int]:
+    rows: list[Row] = []
+    skipped = 0
+    raised = 0
+    for doc in corpus:
+        lodged_sap = doc.get("energy_rating_current")
+        if lodged_sap is None:
+            skipped += 1
+            continue
+        try:
+            epc = EpcPropertyDataMapper.from_api_response(doc)
+            result = calculate_sap_from_inputs(
+                cert_to_inputs(epc, prices=SAP_10_2_SPEC_PRICES)
+            )
+            # SAP/EI rating is the UK-average rating cascade (`result`);
+            # the EPC-displayed CO2/PE use the postcode demand cascade
+            # (SAP 10.2 Appendix U p.124). Use the demand cascade for the
+            # PE/CO2-vs-cost triage so it is not confounded by the climate
+            # difference (UK-average vs local weather).
+            demand = calculate_sap_from_inputs(
+                cert_to_demand_inputs(epc, prices=SAP_10_2_SPEC_PRICES)
+            )
+        except Exception:
+            raised += 1
+            continue
+        cert = str(
+            doc.get("certificate_number")
+            or doc.get("lmk_key")
+            or doc.get("uprn")
+            or len(rows)
+        )
+        lodged_co2_t = doc.get("co2_emissions_current")
+        lodged_pe = doc.get("energy_consumption_current")
+        rows.append(Row(
+            cert=cert,
+            sap_err=result.sap_score_continuous - lodged_sap,
+            co2_err_t=(demand.co2_kg_per_yr / 1000.0 - lodged_co2_t)
+            if lodged_co2_t is not None else None,
+            pe_err=(demand.primary_energy_kwh_per_m2 - lodged_pe)
+            if lodged_pe is not None else None,
+            lodged_sap=lodged_sap,
+            our_sap=result.sap_score_continuous,
+            lodged_pe=lodged_pe,
+            our_pe=demand.primary_energy_kwh_per_m2,
+            feats=features(doc),
+        ))
+    return rows, skipped, raised
+
+
+def _triage(r: Row) -> str:
+    """Cost vs demand label from the PE/CO2 split (~tolerant)."""
+    if r.pe_err is None or r.co2_err_t is None:
+        return "?"
+    pe_ok = abs(r.pe_err) < 5.0           # kWh/m2/yr
+    co2_ok = abs(r.co2_err_t) < 0.10      # t/yr
+    if pe_ok and co2_ok:
+        return "COST"                      # demand reproduces, cost-side off
+    return "DEMAND"
+
+
+def main() -> None:
+    min_n = 12
+    n_worst = 30
+    if "--min-n" in sys.argv:
+        min_n = int(sys.argv[sys.argv.index("--min-n") + 1])
+    if "--worst" in sys.argv:
+        n_worst = int(sys.argv[sys.argv.index("--worst") + 1])
+
+    rows, skipped, raised = _compute(_load())
+    n = len(rows)
+    within = sum(1 for r in rows if abs(r.sap_err) < 0.5) / n * 100
+    print(
+        f"profiled {n} certs ({skipped} no-lodged-SAP, {raised} raised) | "
+        f"within-0.5 = {within:.1f}% | "
+        f"signed {stats.mean(r.sap_err for r in rows):+.3f} | "
+        f"MAE {stats.mean(abs(r.sap_err) for r in rows):.3f}"
+    )
+    out = [r for r in rows if abs(r.sap_err) >= 0.5]
+    cost_n = sum(1 for r in out if _triage(r) == "COST")
+    dem_n = sum(1 for r in out if _triage(r) == "DEMAND")
+    print(
+        f"of {len(out)} outside-0.5: {dem_n} DEMAND-side (PE/CO2 also off), "
+        f"{cost_n} COST-side (PE/CO2 match), {len(out) - cost_n - dem_n} unknown"
+    )
+    print("=" * 104)
+
+    feat_names = list(rows[0].feats.keys())
+    bucket_lines: list[tuple[float, str]] = []
+    for fn in feat_names:
+        groups: dict[str, list[float]] = defaultdict(list)
+        for r in rows:
+            groups[str(r.feats.get(fn))].append(r.sap_err)
+        for val, es in groups.items():
+            cnt = len(es)
+            if cnt < min_n:
+                continue
+            w05 = sum(1 for e in es if abs(e) < 0.5)
+            mabs = stats.mean(abs(e) for e in es)
+            waste = (cnt - w05) * mabs
+            bucket_lines.append((waste, (
+                f"  {fn:22s}={val:<20.20s} n={cnt:4d} "
+                f"within0.5={w05 / cnt * 100:4.0f}% "
+                f"signed={stats.mean(es):+6.2f} mean|err|={mabs:5.2f} "
+                f"[waste={waste:6.0f}]"
+            )))
+    print(f"TOP ERROR-CARRYING BUCKETS (n_out x mean|err|; min-n={min_n}):")
+    for _, line in sorted(bucket_lines, key=lambda x: -x[0])[:40]:
+        print(line)
+
+    print("=" * 104)
+    print(f"WORST {n_worst} OVER-RATERS (our SAP too high -> we under-count loss/cost):")
+    _dump_worst(sorted(rows, key=lambda r: -r.sap_err)[:n_worst])
+    print("-" * 104)
+    print(f"WORST {n_worst} UNDER-RATERS (our SAP too low -> we over-count loss/cost):")
+    _dump_worst(sorted(rows, key=lambda r: r.sap_err)[:n_worst])
+
+
+def _dump_worst(rows: list[Row]) -> None:
+    print(
+        f"  {'cert':>16s} {'lodgSAP':>7s} {'ourSAP':>7s} {'dSAP':>6s} "
+        f"{'dPE':>6s} {'dCO2t':>6s} {'split':>6s}  "
+        f"heat/prop/wall/roof/fuel"
+    )
+    for r in rows:
+        f = r.feats
+        sig = (
+            f"{f.get('main_sap_code')}/{f.get('property_type')}/"
+            f"{f.get('wall_construction')}/{f.get('roof_codes')}/"
+            f"{f.get('main_fuel')} pcdb={f.get('has_pcdb_main')} "
+            f"2nd={f.get('has_secondary')} pv={f.get('has_pv')}"
+        )
+        pe = f"{r.pe_err:+6.1f}" if r.pe_err is not None else "     ?"
+        co2 = f"{r.co2_err_t:+6.2f}" if r.co2_err_t is not None else "     ?"
+        print(
+            f"  {r.cert:>16.16s} {r.lodged_sap:7.1f} {r.our_sap:7.2f} "
+            f"{r.sap_err:+6.2f} {pe} {co2} {_triage(r):>6s}  {sig}"
+        )
+
+
+if __name__ == "__main__":
+    main()
diff --git a/tests/domain/modelling/test_elmhurst_cascade_pins.py b/tests/domain/modelling/test_elmhurst_cascade_pins.py
index 0e6832b7..19186eae 100644
--- a/tests/domain/modelling/test_elmhurst_cascade_pins.py
+++ b/tests/domain/modelling/test_elmhurst_cascade_pins.py
@@ -686,12 +686,15 @@ def test_ashp_overlay_scores_the_vaillant_end_state_from_a_gas_boiler() -> None:
     # dwelling's baseline fabric and so the ASHP end-state SAP. Still a snapshot
     # of the Vaillant overlay's own output, validated transitively by the
     # system-boiler pin below (which reproduces a real Vaillant cert at delta 0).
+    # CO2/PE are the postcode DEMAND cascade now that `Sap10Calculator.
+    # calculate` computes EPC emissions/PE on local weather (SAP 10.2
+    # Appendix U p.124); SAP is unchanged (UK-average rating cascade).
     _assert_overlay_scores(
         before,
         option.overlay,
         sap=51.99820176096402,
-        co2=1268.4645083243888,
-        pe=13080.20756425629,
+        co2=1065.7593506066496,
+        pe=10995.781557709413,
     )
 
 
@@ -715,12 +718,14 @@ def test_ashp_overlay_scores_the_vaillant_end_state_from_a_gas_boiler_instant_hw
     # boiler-1 pin above); the same merge also resolved this cert's main-fuel
     # mapper gap (§14.2 mains-gas derivation), so its raw before now baselines —
     # see `test_gas_boiler_instant_hw_before_baselines`.
+    # CO2/PE are the postcode DEMAND cascade now (see the boiler-1 pin above);
+    # SAP is unchanged (UK-average rating cascade).
     _assert_overlay_scores(
         before,
         option.overlay,
         sap=39.00740809309464,
-        co2=2248.6089062232704,
-        pe=23094.10189037302,
+        co2=1845.8588018295509,
+        pe=18944.42568846759,
     )
 
 
diff --git a/tests/domain/sap10_calculator/rdsap/test_cert_to_inputs.py b/tests/domain/sap10_calculator/rdsap/test_cert_to_inputs.py
index 24d594f7..d8934c16 100644
--- a/tests/domain/sap10_calculator/rdsap/test_cert_to_inputs.py
+++ b/tests/domain/sap10_calculator/rdsap/test_cert_to_inputs.py
@@ -38,6 +38,7 @@ from datatypes.epc.domain.epc_property_data import (
 from domain.sap10_ml.tests._fixtures import (
     make_building_part,
     make_floor_dimension,
+    make_main_heating_detail,
     make_minimal_sap10_epc,
     make_sap_heating,
     make_window,
@@ -79,6 +80,7 @@ from domain.sap10_calculator.rdsap.cert_to_inputs import (
     _pv_overshading_factor,  # pyright: ignore[reportPrivateUsage]
     _pv_pitch_deg,  # pyright: ignore[reportPrivateUsage]
     _responsiveness,  # pyright: ignore[reportPrivateUsage]
+    _secondary_fuel_code,  # pyright: ignore[reportPrivateUsage]
     _secondary_fuel_cost_gbp_per_kwh,  # pyright: ignore[reportPrivateUsage]
     _secondary_heating_fraction_for_category,  # pyright: ignore[reportPrivateUsage]
     _section_12_4_4_summer_immersion_applies,  # pyright: ignore[reportPrivateUsage]
@@ -2161,6 +2163,47 @@ def test_is_electric_main_dual_fuel_table_32_code_10_is_not_electric() -> None:
     assert _is_electric_main(community_electric_main) is False
 
 
+def test_dual_fuel_secondary_api_enum_9_prices_as_dual_fuel_not_lpg() -> None:
+    # Arrange — the gov-API lodges secondary fuel enum 9 = "dual fuel (mineral
+    # and wood)", but enum value 9 COLLIDES with the same-valued RdSAP 10
+    # Table 32 / SAP 10.2 Table 12 code 9 = "LPG (bulk, SC11F)". The secondary
+    # cost + CO2/PE paths previously took the same-value lookup (LPG 3.48
+    # p/kWh, CO2 0.241 kg/kWh) instead of translating the enum to the dual-
+    # fuel row (3.99 p/kWh, CO2 0.087) — under-costing the secondary (SAP
+    # over-rate) AND over-counting its CO2 (LPG is fossil; dual fuel is part
+    # wood). Enum 9 is now in `_GOV_API_COLLISION_FUELS`, and both secondary
+    # paths canonicalise (mirroring the main-fuel boundary). SAP 10.2 Table
+    # 12 (p.189) / RdSAP 10 Table 32 (p.95).
+    gas_boiler_main = MainHeatingDetail(
+        has_fghrs=False, main_fuel_type=26, heat_emitter_type=1,
+        emitter_temperature=1, main_heating_control=2106,
+        main_heating_category=2, sap_main_heating_code=102,
+    )
+    dual_fuel_secondary_epc = make_minimal_sap10_epc(
+        total_floor_area_m2=_TYPICAL_TFA_M2,
+        habitable_rooms_count=4,
+        country_code="ENG",
+        sap_heating=make_sap_heating(
+            main_heating_details=[gas_boiler_main],
+            secondary_fuel_type=9,  # gov-API enum: dual fuel (mineral + wood)
+            secondary_heating_type=631,
+        ),
+    )
+
+    # Act — the rating-cascade secondary price + the CO2/PE fuel code.
+    secondary_rate_gbp_per_kwh = _secondary_fuel_cost_gbp_per_kwh(
+        dual_fuel_secondary_epc.sap_heating,
+        gas_boiler_main,
+        2,  # standard (single-rate) meter
+        SAP_10_2_SPEC_PRICES,
+    )
+    secondary_factor_code = _secondary_fuel_code(dual_fuel_secondary_epc)
+
+    # Assert — dual fuel 3.99 p/kWh (NOT LPG 3.48) + Table code 10 (NOT 9).
+    assert abs(secondary_rate_gbp_per_kwh - 0.0399) <= 1e-6
+    assert secondary_factor_code == 10
+
+
 def test_is_electric_water_dual_fuel_table_32_code_10_is_not_electric() -> None:
     # Arrange — same API/Table 32 collision as `_is_electric_main` per
     # S0380.136 docstring.
@@ -7581,3 +7624,55 @@ def test_index_less_mev_applies_table_4g_note_3_default_data_iuf() -> None:
     # 2.5x the raw-0.8 value, not the raw default.
     assert fan_kwh > 0.0
     assert abs(fan_kwh - expected) <= 1e-9
+
+
+def test_heat_pump_water_scop_not_applied_to_separate_immersion_dhw() -> None:
+    # Arrange — SAP 10.2 Appendix N3.7(a): a heat pump's PCDB water
+    # efficiency (η_water) applies to the DHW ONLY when the cylinder is
+    # heated BY the heat pump. A separate electric immersion (WHC 903) heats
+    # the water at 100% regardless of the space-heating system, so the HP's
+    # water SCOP must NOT leak onto it. Invariant: a WHC-903 immersion's
+    # hot-water fuel is INDEPENDENT of the main — a heat-pump main and a gas-
+    # boiler main yield the SAME immersion fuel (both 100%, no primary loss).
+    # Before the fix the APM override set η_water = 187.5% × 0.6 in-use =
+    # 112.5% on the HP cert, under-counting its immersion fuel. Worksheet-
+    # validated on simulated case 45: water (62) = 2130.26 kWh at η_water=100%,
+    # not 2130.26 / 1.125 = 1893.57.
+    hp_main = make_main_heating_detail(
+        main_fuel_type=29,  # electricity
+        heat_emitter_type=1,
+        main_heating_category=4,  # heat pump
+        main_heating_index_number=100053,  # PCDB Table 362 ASHP (ECODAN 5 kW)
+        main_heating_data_source=1,
+    )
+    boiler_main = make_main_heating_detail(
+        main_fuel_type=26,  # mains gas
+        heat_emitter_type=1,
+        main_heating_category=2,  # gas boiler
+        sap_main_heating_code=102,
+    )
+
+    def _immersion_epc(main: MainHeatingDetail) -> EpcPropertyData:
+        return make_minimal_sap10_epc(
+            total_floor_area_m2=_TYPICAL_TFA_M2,
+            habitable_rooms_count=4,
+            country_code="ENG",
+            has_hot_water_cylinder=True,
+            sap_heating=make_sap_heating(
+                main_heating_details=[main],
+                water_heating_code=903,  # separate electric immersion
+                water_heating_fuel=30,  # standard electricity
+                cylinder_size=2,
+                cylinder_insulation_type=1,
+                cylinder_insulation_thickness_mm=25,
+            ),
+        )
+
+    # Act
+    hp_fuel = cert_to_inputs(_immersion_epc(hp_main)).hot_water_kwh_per_yr
+    boiler_fuel = cert_to_inputs(_immersion_epc(boiler_main)).hot_water_kwh_per_yr
+
+    # Assert — the immersion DHW fuel is identical whether the space main is a
+    # heat pump or a gas boiler (the HP water SCOP does not apply to it).
+    assert hp_fuel > 0.0
+    assert abs(hp_fuel - boiler_fuel) <= 1e-6
diff --git a/tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_001431_case45.py b/tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_001431_case45.py
new file mode 100644
index 00000000..7d9ab95f
--- /dev/null
+++ b/tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_001431_case45.py
@@ -0,0 +1,107 @@
+"""Mapper-driven cascade pin against the Elmhurst P960-0001-001431
+"simulated case 45" worksheet — a ~47 m² GROUND-FLOOR FLAT heated by an
+air-source HEAT PUMP (PCDB 100053 ECODAN, radiators, MCS=No) with a
+WHC-903 electric-immersion DHW and a 110 L cylinder, postcode W6 9BF
+(SAP Region "Thames Valley").
+
+Case 45 is the 1e-4 oracle for the SAP 10.2 Appendix U (PDF p.124) TWO-
+CLIMATE-CASCADE split. The P960 prints the current dwelling TWICE:
+
+  * Block 1 — "11a. SAP rating / 12a. CO2" — computed on UK-AVERAGE
+    weather (Appendix U Tables U1-U3 region 0). Drives the SAP/EI rating.
+    Space-heat demand (98c) = 7333.79; SAP value (258) = 60.5318 (-> 61);
+    total CO2 (272) = 692.13.
+  * Block 2 — "CALCULATION OF EPC COSTS, EMISSIONS AND PRIMARY ENERGY" —
+    computed on POSTCODE-DISTRICT weather (PCDB Table 172, W6). Drives the
+    EPC-displayed figures. Space-heat demand (98c) = 5921.05; total CO2
+    (272) = 626.78; total primary energy (286) = 6581.59.
+
+Per Appendix U paragraph 1: "Other calculations (such as for energy use
+and costs on EPCs) are done using local weather." `Sap10Calculator.
+calculate` therefore runs both cascades and grafts the demand cascade's
+CO2/PE onto the rating cascade's SAP — this fixture pins BOTH.
+
+Like the other `_elmhurst_worksheet_001431_case*` fixtures it does NOT
+hand-build the EpcPropertyData: it routes the Summary PDF through
+ElmhurstSiteNotesExtractor + from_elmhurst_site_notes so the pin exercises
+the WHOLE extractor + mapper + calculator pipeline.
+
+Source: user-simulated PDFs at `sap worksheets/golden fixture debugging/
+simulated case 45/`. The Summary is mirrored into the tracked
+`backend/documents_parser/tests/fixtures/Summary_001431_case45.pdf` so the
+test runs without depending on the unstaged workspace.
+
+Per [[feedback-zero-error-strict]]: pins are abs <= 1e-4 against the PDF.
+"""
+
+from __future__ import annotations
+
+import re
+import subprocess
+from pathlib import Path
+from typing import Final
+
+from backend.documents_parser.elmhurst_extractor import ElmhurstSiteNotesExtractor
+from datatypes.epc.domain.epc_property_data import EpcPropertyData
+from datatypes.epc.domain.mapper import EpcPropertyDataMapper
+
+# parents[0]=worksheet/, [1]=sap10_calculator/, [2]=domain/, [3]=tests/,
+# [4]=repo root.
+_SUMMARY_PDF: Final[Path] = (
+    Path(__file__).resolve().parents[4]
+    / "backend" / "documents_parser" / "tests" / "fixtures"
+    / "Summary_001431_case45.pdf"
+)
+
+# Block 1 — UK-average RATING cascade (`cert_to_inputs`).
+RATING_SPACE_HEATING_KWH: Final[float] = 7333.7892    # (98c)
+RATING_SAP_CONTINUOUS: Final[float] = 60.5318         # (258) un-rounded
+RATING_SAP_INTEGER: Final[int] = 61                   # (258)
+RATING_CO2_KG_PER_YR: Final[float] = 692.1287         # (272)
+
+# Block 2 — POSTCODE-district DEMAND cascade (`cert_to_demand_inputs`).
+DEMAND_SPACE_HEATING_KWH: Final[float] = 5921.0486    # (98c)
+DEMAND_CO2_KG_PER_YR: Final[float] = 626.7797         # (272)
+DEMAND_PRIMARY_ENERGY_KWH: Final[float] = 6581.5936   # (286)
+
+
+def _summary_pdf_to_textract_style_pages(pdf_path: Path) -> list[str]:
+    """Convert a Summary PDF into the per-page text format the
+    ElmhurstSiteNotesExtractor expects (label/value token sequences).
+    Mirror of the helper in the other `_elmhurst_worksheet_*` fixtures.
+    """
+    info = subprocess.run(
+        ["pdfinfo", str(pdf_path)], capture_output=True, text=True, check=True,
+    ).stdout
+    m = re.search(r"Pages:\s+(\d+)", info)
+    if m is None:
+        raise RuntimeError(f"Could not parse page count from {pdf_path}")
+    page_count = int(m.group(1))
+    pages: list[str] = []
+    for i in range(1, page_count + 1):
+        layout = subprocess.run(
+            [
+                "pdftotext", "-layout", "-f", str(i), "-l", str(i),
+                str(pdf_path), "-",
+            ],
+            capture_output=True, text=True, check=True,
+        ).stdout
+        tokens: list[str] = []
+        for line in layout.splitlines():
+            if not line.strip():
+                tokens.append("")
+                continue
+            parts = [p for p in re.split(r"\s{2,}", line.strip()) if p]
+            tokens.extend(parts)
+        pages.append("\n".join(tokens))
+    return pages
+
+
+def build_epc() -> EpcPropertyData:
+    """Route the simulated case-45 Summary through extractor + mapper.
+    No hand-built EpcPropertyData — the extractor and mapper are part of
+    the test target. This module is a pin PROVIDER (build_epc + constants);
+    the collected assertions live in `test_section_cascade_pins`."""
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_PDF)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+    return EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)
diff --git a/tests/domain/sap10_calculator/worksheet/test_e2e_elmhurst_sap_score.py b/tests/domain/sap10_calculator/worksheet/test_e2e_elmhurst_sap_score.py
index 1637f281..1625bcbc 100644
--- a/tests/domain/sap10_calculator/worksheet/test_e2e_elmhurst_sap_score.py
+++ b/tests/domain/sap10_calculator/worksheet/test_e2e_elmhurst_sap_score.py
@@ -24,7 +24,10 @@ from typing import Final
 
 import pytest
 
-from domain.sap10_calculator.calculator import Sap10Calculator
+from domain.sap10_calculator.calculator import (
+    Sap10Calculator,
+    calculate_sap_from_inputs,
+)
 from domain.sap10_calculator.rdsap.cert_to_inputs import (
     cert_to_inputs,
     water_heating_section_from_cert,
@@ -338,8 +341,13 @@ def test_sap_result_pin(fixture_name: str, field_name: str) -> None:
     epc = _FIXTURE_MODULES[fixture_name].build_epc()
     expected = getattr(pin, field_name)
 
-    # Act
-    result = Sap10Calculator().calculate(epc)
+    # Act — these pins are the worksheet's Block-1 (energy-rating) line refs,
+    # i.e. the UK-average RATING cascade. `Sap10Calculator.calculate` now
+    # grafts the postcode DEMAND cascade's CO2/PE onto the result (SAP 10.2
+    # Appendix U p.124), so the rating-cascade fields are pinned via
+    # `cert_to_inputs` directly; the demand cascade is pinned separately
+    # (corpus gauge + simulated case 45 Block-2 pins).
+    result = calculate_sap_from_inputs(cert_to_inputs(epc))
     actual = getattr(result, field_name)
 
     # Assert
diff --git a/tests/domain/sap10_calculator/worksheet/test_heat_transmission.py b/tests/domain/sap10_calculator/worksheet/test_heat_transmission.py
index 1f20aeed..213bf2ff 100644
--- a/tests/domain/sap10_calculator/worksheet/test_heat_transmission.py
+++ b/tests/domain/sap10_calculator/worksheet/test_heat_transmission.py
@@ -157,6 +157,70 @@ def test_mixed_flat_pitched_roof_does_not_contaminate_pitched_u_value() -> None:
     assert abs(result.roof_w_per_k - 44.6) <= 2.0
 
 
+def test_ground_floor_flat_bills_floor_despite_flat_dwelling_type() -> None:
+    # Arrange — a ground-floor flat whose dwelling_type the mapper labelled
+    # "Top-floor flat" (so the dwelling-level exposure heuristic
+    # `_dwelling_exposure` suppresses the floor on the assumption a heated
+    # dwelling sits below), but whose building part lodges a "Ground floor"
+    # floor_type. A ground floor is in contact with the ground (RdSAP 10
+    # §3.12) -> heat-loss floor. The Elmhurst Summary path lodges this as a
+    # "Ground floor" floor_type (not the API floor_heat_loss=1 exposed code),
+    # so without the per-part ground signal the cascade dropped the floor.
+    # Worksheet-validated by simulated case 45: (28a) = 47.0 × U=0.54 = 25.38
+    # W/K, billed as 0 before this fix (+7 SAP).
+    ground = make_building_part(
+        identifier=BuildingPartIdentifier.MAIN,
+        construction_age_band="C",
+        floor_type="Ground floor",
+        floor_dimensions=[
+            make_floor_dimension(
+                total_floor_area_m2=47.0, room_height_m=2.4,
+                heat_loss_perimeter_m=15.8, party_wall_length_m=0.0, floor=0,
+            ),
+        ],
+    )
+    epc = make_minimal_sap10_epc(
+        total_floor_area_m2=47.0, country_code="ENG",
+        dwelling_type="Top-floor flat", property_type="Flat",
+        sap_building_parts=[ground],
+    )
+
+    # Act
+    result = heat_transmission_from_cert(epc)
+
+    # Assert — the ground floor carries heat loss (≈ 47 × 0.54), not 0.
+    assert result.floor_w_per_k > 20.0
+
+
+def test_top_floor_flat_with_party_floor_stays_suppressed() -> None:
+    # Arrange — the contrast: a flat lodging "(another dwelling below)" sits
+    # over a heated dwelling, so its floor is a party floor with no heat loss
+    # (RdSAP 10 §3). The ground-floor override must NOT fire — proving the
+    # discriminator is the floor_type, not the flat label.
+    party = make_building_part(
+        identifier=BuildingPartIdentifier.MAIN,
+        construction_age_band="C",
+        floor_type="To another dwelling below",
+        floor_dimensions=[
+            make_floor_dimension(
+                total_floor_area_m2=47.0, room_height_m=2.4,
+                heat_loss_perimeter_m=15.8, party_wall_length_m=0.0, floor=0,
+            ),
+        ],
+    )
+    epc = make_minimal_sap10_epc(
+        total_floor_area_m2=47.0, country_code="ENG",
+        dwelling_type="Top-floor flat", property_type="Flat",
+        sap_building_parts=[party],
+    )
+
+    # Act
+    result = heat_transmission_from_cert(epc)
+
+    # Assert — party floor, no heat loss.
+    assert result.floor_w_per_k == 0.0
+
+
 def test_part_geometry_floorless_part_honours_full_key_contract() -> None:
     # Arrange — a building part lodged with NO sap_floor_dimensions (e.g.
     # a party-wall-only or RR-only extension; observed on 5 certs in a
diff --git a/tests/domain/sap10_calculator/worksheet/test_section_cascade_pins.py b/tests/domain/sap10_calculator/worksheet/test_section_cascade_pins.py
index 6547a585..ce93e21c 100644
--- a/tests/domain/sap10_calculator/worksheet/test_section_cascade_pins.py
+++ b/tests/domain/sap10_calculator/worksheet/test_section_cascade_pins.py
@@ -46,6 +46,7 @@ from tests.domain.sap10_calculator.worksheet import (
     _elmhurst_worksheet_001431_case21 as _w001431_case21,
     _elmhurst_worksheet_001431_case43 as _w001431_case43,
     _elmhurst_worksheet_001431_case44 as _w001431_case44,
+    _elmhurst_worksheet_001431_case45 as _w001431_case45,
 )
 
 
@@ -491,6 +492,67 @@ def test_case44_blower_door_pressure_test_matches_pdf() -> None:
     _pin(vent.effective_monthly_ach[0], 0.5812, "§2 (25) Jan case44")
 
 
+def test_case45_heat_pump_two_climate_cascade_matches_pdf() -> None:
+    """Simulated case 45 (heat-pump ground-floor flat, postcode W6) is the
+    1e-4 oracle for the SAP 10.2 Appendix U (p.124) two-climate-cascade
+    split. The P960 prints the current dwelling twice:
+
+      * Block 1 ("11a SAP rating / 12a CO2") on UK-AVERAGE weather (region
+        0): space heat (98c) 7333.79, SAP (258) 60.5318, CO2 (272) 692.13.
+      * Block 2 ("EPC COSTS, EMISSIONS AND PRIMARY ENERGY") on POSTCODE
+        weather (PCDB Table 172, W6): space heat (98c) 5921.05, CO2 (272)
+        626.78, primary energy (286) 6581.59.
+
+    The SAP/EI rating reads the rating cascade; the EPC-displayed CO2/PE
+    read the demand cascade. Pins both ends at abs=1e-4."""
+    # Arrange
+    from domain.sap10_calculator.calculator import calculate_sap_from_inputs
+    from domain.sap10_calculator.rdsap.cert_to_inputs import cert_to_demand_inputs
+
+    epc = _w001431_case45.build_epc()
+    # The split only exists because the postcode resolves to local weather.
+    assert local_climate_for_cert(epc) is not None
+
+    # Act — both climate cascades from the one cert.
+    rating = calculate_sap_from_inputs(cert_to_inputs(epc))
+    demand = calculate_sap_from_inputs(cert_to_demand_inputs(epc))
+
+    # Assert — Block 1 (UK-average rating cascade).
+    _pin(
+        rating.space_heating_kwh_per_yr,
+        _w001431_case45.RATING_SPACE_HEATING_KWH,
+        "(98c) rating case45",
+    )
+    _pin(
+        rating.sap_score_continuous,
+        _w001431_case45.RATING_SAP_CONTINUOUS,
+        "(258) rating case45",
+    )
+    assert rating.sap_score == _w001431_case45.RATING_SAP_INTEGER
+    _pin(
+        rating.co2_kg_per_yr,
+        _w001431_case45.RATING_CO2_KG_PER_YR,
+        "(272) rating case45",
+    )
+
+    # Assert — Block 2 (postcode demand cascade).
+    _pin(
+        demand.space_heating_kwh_per_yr,
+        _w001431_case45.DEMAND_SPACE_HEATING_KWH,
+        "(98c) demand case45",
+    )
+    _pin(
+        demand.co2_kg_per_yr,
+        _w001431_case45.DEMAND_CO2_KG_PER_YR,
+        "(272) demand case45",
+    )
+    _pin(
+        demand.primary_energy_kwh_per_yr,
+        _w001431_case45.DEMAND_PRIMARY_ENERGY_KWH,
+        "(286) demand case45",
+    )
+
+
 def test_case6_main_2_emitter_and_control_extracted() -> None:
     """Simulated case 6's §14.1 Main Heating2 lodges its OWN emitter
     ("Underfloor Heating") and control ("SAP code 2110, ...") — the two
diff --git a/tests/infrastructure/epc_client/test_sap_accuracy_corpus.py b/tests/infrastructure/epc_client/test_sap_accuracy_corpus.py
index 9aed0f34..ef933adb 100644
--- a/tests/infrastructure/epc_client/test_sap_accuracy_corpus.py
+++ b/tests/infrastructure/epc_client/test_sap_accuracy_corpus.py
@@ -30,11 +30,7 @@ from typing import Any
 import pytest
 
 from datatypes.epc.domain.mapper import EpcPropertyDataMapper
-from domain.sap10_calculator.calculator import calculate_sap_from_inputs
-from domain.sap10_calculator.rdsap.cert_to_inputs import (
-    SAP_10_2_SPEC_PRICES,
-    cert_to_inputs,
-)
+from domain.sap10_calculator.calculator import Sap10Calculator
 
 _CORPUS = Path(
     "backend/epc_api/json_samples/RdSAP-Schema-21.0.1/corpus.jsonl"
@@ -119,10 +115,45 @@ _CORPUS = Path(
 # 100010129331 (roof 110.5 -> 31.3 W/K, +13.1 -> -0.05 SAP). within-0.5
 # 68.8% -> 69.5% (MAE 0.888 -> 0.859; PE 13.9 -> 13.6); 3-part cohort 56% ->
 # 61%. Pinned in test_heat_transmission (by_kind split + no-contamination).
-_MIN_WITHIN_HALF_SAP = 0.69
-_MAX_SAP_MAE = 0.86
-_MAX_CO2_MAE_TONNES = 0.30      # t CO2 / yr vs co2_emissions_current
-_MAX_PE_PER_M2_MAE = 14.0       # kWh / m2 / yr vs energy_consumption_current
+# GROUND-FLOOR FLAT FLOOR EXPOSURE (RdSAP 10 §3.12): a ground-floor flat whose
+# dwelling_type the mapper labelled "Top-floor flat" had its ground floor (in
+# contact with the ground -> heat loss) dropped, because the flat exposure
+# heuristic keys on dwelling_type and the Summary path lodges the position as a
+# "Ground floor" floor_type (not the API floor_heat_loss=1 code). Treating a
+# "ground floor" floor_type as exposed (worksheet-validated to 1e-4 on simulated
+# case 45: floor (28a) 0 -> 25.38 W/K, fabric (33) 75.6 -> 101.01) -> 69.5% ->
+# 69.7% (MAE 0.859 -> 0.854). Pinned in test_heat_transmission.
+# POSTCODE DEMAND CASCADE (SAP 10.2 Appendix U paragraph 1, p.124): the
+# CO2/PE over-estimate diagnosed above as "per-cert mapper/demand fidelity"
+# was largely a CLIMATE-cascade bug. The SAP/EI rating is computed on
+# UK-average weather (Tables U1-U3 region 0), but EPC-displayed energy use,
+# CO2 emissions and primary energy use POSTCODE-DISTRICT weather from PCDB
+# Table 172 — "other calculations (such as for energy use and costs on EPCs)
+# are done using local weather". We were feeding the UK-average demand to all
+# three outputs, so warm-region certs (most of England, warmer than the
+# UK-average) over-counted heating demand → CO2/PE high. `Sap10Calculator.
+# calculate` now grafts the demand cascade's CO2/PE onto the rating cascade's
+# SAP. Across the corpus this moved CO2 MAE 0.26 -> 0.12 t/yr (bias +0.18 ->
+# +0.04) and PE MAE 13.6 -> 3.8 kWh/m2/yr (bias +9.0 -> +0.24); SAP unchanged
+# (rating cascade). Worksheet-validated to 1e-4 on simulated case 45 (rating
+# CO2 692.13; demand CO2 626.78, PE 6581.59). The residual PE/CO2 spread is
+# now the genuine per-cert mapper-fidelity tail.
+# DUAL-FUEL SECONDARY COLLISION (RdSAP 10 Table 32 / SAP 10.2 Table 12): the
+# gov-API lodges fuel enum 9 ("dual fuel, mineral and wood") for a dual-fuel
+# room heater, but enum 9 collides with the same-valued Table-32/12 code 9
+# (LPG SC11F), so the price (3.48 vs dual-fuel 3.99 p/kWh) AND the CO2/PE
+# factors (LPG 0.241 / 1.163 vs dual fuel 0.087 / 1.049) resolved to LPG —
+# the secondary was under-costed (→ SAP over-rate) and over-counted on CO2.
+# Canonicalising enum 9 (now in `_GOV_API_COLLISION_FUELS`) on the secondary
+# cost + factor paths took within-0.5 69.7% -> 70.2% (MAE 0.854 -> 0.845;
+# dual-fuel-secondary cohort 42.9% -> 49.0%, signed +0.55 -> +0.41) and CO2
+# MAE 0.12 -> 0.08 t/yr (bias +0.04 -> 0.00). A prior session deferred enum 9
+# ("direction not understood") while the PE/CO2 lens was confounded by the
+# climate-cascade bug (fc7c4d2d); the corrected lens shows the over-rate.
+_MIN_WITHIN_HALF_SAP = 0.70
+_MAX_SAP_MAE = 0.85
+_MAX_CO2_MAE_TONNES = 0.09      # t CO2 / yr vs co2_emissions_current
+_MAX_PE_PER_M2_MAE = 4.0        # kWh / m2 / yr vs energy_consumption_current
 
 
 def _load_corpus() -> list[dict[str, Any]]:
@@ -147,8 +178,12 @@ def test_api_path_sap_accuracy_on_rdsap_21_0_1_corpus(
     co2_signed_errs_t: list[float] = []      # our − lodged, tonnes/yr
     pe_signed_errs: list[float] = []          # our − lodged, kWh/m²/yr
     skipped = 0
+    _calculator = Sap10Calculator()
 
     # Act — run the API → EpcPropertyData → calculator pipeline per cert.
+    # `Sap10Calculator.calculate` runs both climate cascades (SAP 10.2
+    # Appendix U p.124): the SAP rating on UK-average weather, CO2/PE on
+    # postcode-district weather — exactly the two figures the EPC lodges.
     for doc in corpus:
         lodged_sap = doc.get("energy_rating_current")
         if lodged_sap is None:
@@ -156,9 +191,7 @@ def test_api_path_sap_accuracy_on_rdsap_21_0_1_corpus(
             continue
         try:
             epc = EpcPropertyDataMapper.from_api_response(doc)
-            result = calculate_sap_from_inputs(
-                cert_to_inputs(epc, prices=SAP_10_2_SPEC_PRICES)
-            )
+            result = _calculator.calculate(epc)
         except Exception:
             # A mapper / calculator raise is a coverage gap tracked elsewhere
             # (eval_api_sap_accuracy.py); here we gauge the certs that compute.