From 5e7e51d8b2e12262c27bc84c66c4a148f2969363 Mon Sep 17 00:00:00 2001 From: Khalim Conn-Kowlessar Date: Fri, 3 Jul 2026 09:11:38 +0000 Subject: [PATCH 1/8] =?UTF-8?q?An=20electric=20room=20heaters=20override?= =?UTF-8?q?=20sets=20the=20room-heater=20heating=20category=20=F0=9F=9F=A5?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Co-Authored-By: Claude Opus 4.8 --- .../epc/test_main_heating_system_overlay.py | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/tests/domain/epc/test_main_heating_system_overlay.py b/tests/domain/epc/test_main_heating_system_overlay.py index dae992cba..27eb6625b 100644 --- a/tests/domain/epc/test_main_heating_system_overlay.py +++ b/tests/domain/epc/test_main_heating_system_overlay.py @@ -58,6 +58,22 @@ def test_electric_room_heaters_assume_a_dual_economy7_meter() -> None: assert simulation.heating.meter_type == "Dual" +def test_electric_room_heaters_overlay_the_room_heater_category() -> None: + # A landlord "Electric room heaters" override replaces the lodged system, so + # the overlay must stamp the room-heater heating category (SAP Table 4a + # Category 10). Leaving it unset lets a replaced storage heater's category 7 + # survive onto the effective cert, which the SAP 10.2 Table 12a resolver + # (keyed on category) mis-reads as off-peak storage and bills the peaky room + # heaters at the all-night low rate. + # Act + simulation = main_heating_overlay_for("Electric room heaters", 0) + + # Assert — SAP Table 4a Category 10 (Room heaters). + assert simulation is not None + assert simulation.heating is not None + assert simulation.heating.main_heating_category == 10 + + @pytest.mark.parametrize( ("main_heating_value", "code"), [ From bf032d17d09d571ba1ef10804f6c23011993c666 Mon Sep 17 00:00:00 2001 From: Khalim Conn-Kowlessar Date: Fri, 3 Jul 2026 09:12:19 +0000 Subject: [PATCH 2/8] =?UTF-8?q?An=20electric=20room=20heaters=20override?= =?UTF-8?q?=20sets=20the=20room-heater=20heating=20category=20=F0=9F=9F=A9?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Category 10 (SAP Table 4a Room heaters) now overlaid for electric room heaters (691-701), so a replaced storage heater's category 7 no longer survives onto the effective cert and mis-bills via the Table 12a resolver. Co-Authored-By: Claude Opus 4.8 --- domain/epc/property_overlays/main_heating_system_overlay.py | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/domain/epc/property_overlays/main_heating_system_overlay.py b/domain/epc/property_overlays/main_heating_system_overlay.py index 466466594..2e046dd90 100644 --- a/domain/epc/property_overlays/main_heating_system_overlay.py +++ b/domain/epc/property_overlays/main_heating_system_overlay.py @@ -280,7 +280,7 @@ def _category_for(code: int) -> Optional[int]: category 7); without it a storage override left a stale category behind, which the SAP 10.2 Table 12a resolver (keyed on category) could misread as a non-storage system and price the off-peak storage heating at the peak rate.""" - if code in _CATEGORY_10_ROOM_HEATER_CODES: + if code in _CATEGORY_10_ROOM_HEATER_CODES or code in _ELECTRIC_ROOM_HEATER_CODES: return _ROOM_HEATER_CATEGORY if code in _STORAGE_HEATER_CODES: return _STORAGE_HEATER_CATEGORY From cfd979950015bb61324337b7ce19078cc8381007 Mon Sep 17 00:00:00 2001 From: Khalim Conn-Kowlessar Date: Fri, 3 Jul 2026 09:13:03 +0000 Subject: [PATCH 3/8] =?UTF-8?q?An=20electric=20room=20heaters=20override?= =?UTF-8?q?=20sets=20the=20room-heater=20charge=20control=20=F0=9F=9F=A5?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Co-Authored-By: Claude Opus 4.8 --- .../epc/test_main_heating_system_overlay.py | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/tests/domain/epc/test_main_heating_system_overlay.py b/tests/domain/epc/test_main_heating_system_overlay.py index 27eb6625b..dff74bccf 100644 --- a/tests/domain/epc/test_main_heating_system_overlay.py +++ b/tests/domain/epc/test_main_heating_system_overlay.py @@ -74,6 +74,22 @@ def test_electric_room_heaters_overlay_the_room_heater_category() -> None: assert simulation.heating.main_heating_category == 10 +def test_electric_room_heaters_overlay_the_room_heater_charge_control() -> None: + # A system-replacing override must stamp its own control, not inherit the + # replaced system's. Electric room heaters take the Table 4e Group 6 + # room-heater control 2601 (+0.3 C, the conservative no-thermostat default, + # matching the gas/oil/solid room heaters). Leaving it unset lets a replaced + # storage heater's manual charge control 2401 (+0.7 C) survive and over-warm + # the modelled dwelling. + # Act + simulation = main_heating_overlay_for("Electric room heaters", 0) + + # Assert — SAP Table 4e Group 6 room-heater control. + assert simulation is not None + assert simulation.heating is not None + assert simulation.heating.main_heating_control == 2601 + + @pytest.mark.parametrize( ("main_heating_value", "code"), [ From ffd21689fd96d05b82c2cd127d2097c06f8f1d22 Mon Sep 17 00:00:00 2001 From: Khalim Conn-Kowlessar Date: Fri, 3 Jul 2026 09:13:32 +0000 Subject: [PATCH 4/8] =?UTF-8?q?An=20electric=20room=20heaters=20override?= =?UTF-8?q?=20sets=20the=20room-heater=20charge=20control=20=F0=9F=9F=A9?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Control 2601 (SAP Table 4e Group 6 room-heater, +0.3 C conservative default) now overlaid for electric room heaters, matching the gas/oil/ solid siblings, so a replaced storage heater's manual charge control 2401 (+0.7 C) no longer survives and over-warms the modelled dwelling. Co-Authored-By: Claude Opus 4.8 --- domain/epc/property_overlays/main_heating_system_overlay.py | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/domain/epc/property_overlays/main_heating_system_overlay.py b/domain/epc/property_overlays/main_heating_system_overlay.py index 2e046dd90..9782174e3 100644 --- a/domain/epc/property_overlays/main_heating_system_overlay.py +++ b/domain/epc/property_overlays/main_heating_system_overlay.py @@ -266,7 +266,7 @@ def _control_for(code: int) -> Optional[int]: return _MANUAL_CHARGE_CONTROL if code in _GAS_BOILER_CODES: return _FULL_BOILER_CONTROL - if code in _CATEGORY_10_ROOM_HEATER_CODES: + if code in _CATEGORY_10_ROOM_HEATER_CODES or code in _ELECTRIC_ROOM_HEATER_CODES: return _ROOM_HEATER_CONTROL return None From ea113b58fbb03380d701116041a562975cd872cb Mon Sep 17 00:00:00 2001 From: Khalim Conn-Kowlessar Date: Fri, 3 Jul 2026 09:15:31 +0000 Subject: [PATCH 5/8] =?UTF-8?q?The=20overlay=20logs=20an=20error=20when=20?= =?UTF-8?q?it=20cannot=20complete=20a=20heating=20companion=20set=20?= =?UTF-8?q?=F0=9F=9F=A5?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Co-Authored-By: Claude Opus 4.8 --- .../epc/test_main_heating_system_overlay.py | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/tests/domain/epc/test_main_heating_system_overlay.py b/tests/domain/epc/test_main_heating_system_overlay.py index dff74bccf..266e14415 100644 --- a/tests/domain/epc/test_main_heating_system_overlay.py +++ b/tests/domain/epc/test_main_heating_system_overlay.py @@ -6,6 +6,8 @@ calculator reads from the primary system; the overlay is whole-dwelling. from __future__ import annotations +import logging + import pytest from domain.epc.property_overrides.main_heating_system_type import MainHeatingSystemType @@ -90,6 +92,22 @@ def test_electric_room_heaters_overlay_the_room_heater_charge_control() -> None: assert simulation.heating.main_heating_control == 2601 +def test_overlay_logs_when_it_cannot_complete_a_companion_set( + caplog: pytest.LogCaptureFixture, +) -> None: + # An archetype the overlay cannot yet fully companion — here an air-source + # heat pump, whose Table 4e Group 2 conservative control is not yet mapped — + # is still overlaid (log-and-continue), but the incomplete companion set is + # logged as an error so the known gap is visible (CloudWatch) rather than + # silently inheriting the replaced system's stale value. + # Act + with caplog.at_level(logging.ERROR): + main_heating_overlay_for("Air source heat pump", 0) + + # Assert — the gap is reported and names the archetype. + assert "Air source heat pump" in caplog.text + + @pytest.mark.parametrize( ("main_heating_value", "code"), [ From 390e3e89d791a765ea0dd0be4acffbb313557d6f Mon Sep 17 00:00:00 2001 From: Khalim Conn-Kowlessar Date: Fri, 3 Jul 2026 09:16:25 +0000 Subject: [PATCH 6/8] =?UTF-8?q?The=20overlay=20logs=20an=20error=20when=20?= =?UTF-8?q?it=20cannot=20complete=20a=20heating=20companion=20set=20?= =?UTF-8?q?=F0=9F=9F=A9?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit A system-replacing override whose category or control is not yet mapped now logs an error naming the archetype and code, so the incomplete companion set (which otherwise silently inherits the replaced system's value) is visible for review — log-and-continue, matching flag_fuel_mismatch. Co-Authored-By: Claude Opus 4.8 --- .../main_heating_system_overlay.py | 26 +++++++++++++++++-- 1 file changed, 24 insertions(+), 2 deletions(-) diff --git a/domain/epc/property_overlays/main_heating_system_overlay.py b/domain/epc/property_overlays/main_heating_system_overlay.py index 9782174e3..d0c498320 100644 --- a/domain/epc/property_overlays/main_heating_system_overlay.py +++ b/domain/epc/property_overlays/main_heating_system_overlay.py @@ -28,6 +28,7 @@ are left UNKNOWN until modelled. Unresolvable values produce no overlay. from __future__ import annotations +import logging from typing import Optional from domain.modelling.simulation import EpcSimulation, HeatingOverlay @@ -35,6 +36,8 @@ from domain.sap10_calculator.tables.table_12a import ( OFF_PEAK_IMPLYING_HEATING_CODES, ) +logger = logging.getLogger(__name__) + # Off-peak (Economy 7) meter. Electric storage / CPSU systems charge overnight at # the low rate and cannot run economically on a single-rate meter; "Dual" lets # the §12 dispatch resolve the specific tariff (storage 7-hour, CPSU 10-hour). @@ -351,13 +354,32 @@ def main_heating_overlay_for( return None if code in _GAS_BOILER_CODES: return EpcSimulation(heating=_gas_boiler_overlay(code)) + category = _category_for(code) + control = _control_for(code) + if category is None or control is None: + # A system-replacing override should stamp a complete, coherent companion + # set; an unmapped category or control leaves the field unset, so the + # effective cert inherits the REPLACED system's value (a silent mis-rating + # — e.g. a room heater keeping a storage heater's category/control). We do + # not yet have confident defaults for every archetype, so log-and-continue + # (matching `flag_fuel_mismatch`) to make the gap visible for review + # rather than raise mid-run. + logger.error( + "Landlord main_heating_system %r (SAP code %d) overlaid with an " + "incomplete companion set (category=%s, control=%s); the effective " + "cert may inherit the replaced system's value — known gap, review", + main_heating_value, + code, + category, + control, + ) return EpcSimulation( heating=HeatingOverlay( sap_main_heating_code=code, - main_heating_category=_category_for(code), + main_heating_category=category, main_fuel_type=_natural_fuel_for(code), meter_type=_meter_for(code), - main_heating_control=_control_for(code), + main_heating_control=control, # A landlord override describes the existing dwelling, so its assumed # off-peak meter must not downgrade a more-off-peak cert meter # (e.g. a 24-hour all-low tariff). Measures, which re-meter for real, From 962a443ed223920205390f8d9d938d74784fb726 Mon Sep 17 00:00:00 2001 From: Khalim Conn-Kowlessar Date: Fri, 3 Jul 2026 09:17:06 +0000 Subject: [PATCH 7/8] =?UTF-8?q?A=20complete=20room-heater=20overlay=20does?= =?UTF-8?q?=20not=20log=20a=20companion=20gap=20=F0=9F=9F=A9?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Co-Authored-By: Claude Opus 4.8 --- .../domain/epc/test_main_heating_system_overlay.py | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/tests/domain/epc/test_main_heating_system_overlay.py b/tests/domain/epc/test_main_heating_system_overlay.py index 266e14415..40998c7d7 100644 --- a/tests/domain/epc/test_main_heating_system_overlay.py +++ b/tests/domain/epc/test_main_heating_system_overlay.py @@ -108,6 +108,20 @@ def test_overlay_logs_when_it_cannot_complete_a_companion_set( assert "Air source heat pump" in caplog.text +def test_complete_room_heater_overlay_does_not_log_a_companion_gap( + caplog: pytest.LogCaptureFixture, +) -> None: + # Electric room heaters now resolve a full companion set (category 10 + + # control 2601), so the overlay must NOT log an incomplete-companion gap — + # guarding that the fix keeps the set complete. + # Act + with caplog.at_level(logging.ERROR): + main_heating_overlay_for("Electric room heaters", 0) + + # Assert + assert "incomplete companion set" not in caplog.text + + @pytest.mark.parametrize( ("main_heating_value", "code"), [ From 244c5b65edf0b0561cd04f7e0bb5eacb738bee5e Mon Sep 17 00:00:00 2001 From: Khalim Conn-Kowlessar Date: Fri, 3 Jul 2026 09:21:47 +0000 Subject: [PATCH 8/8] Document heating-companion coherence: category/control forced, fuel/meter deferred (ADR-0048) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit ADR-0048 records why a system-replacing heating override must emit a complete companion set — category and control archetype-forced for coherence, fuel and meter deferred where multiple values are valid, and an unmapped companion logged rather than silently inherited. Adds the Heating Companion Set glossary term to CONTEXT.md. Co-Authored-By: Claude Opus 4.8 --- CONTEXT.md | 4 + ...egory-and-control-defers-fuel-and-meter.md | 132 ++++++++++++++++++ 2 files changed, 136 insertions(+) create mode 100644 docs/adr/0048-heating-override-forces-category-and-control-defers-fuel-and-meter.md diff --git a/CONTEXT.md b/CONTEXT.md index e0b4a8493..182959e66 100644 --- a/CONTEXT.md +++ b/CONTEXT.md @@ -103,6 +103,10 @@ _Avoid_: patches (deprecated), corrections, manual EPC, edits **Landlord-Description Classification**: Resolving a **Landlord Description** (unbounded free-text a landlord supplies for one component — "CWI" / "Cav filled" / "cavity insulated" all name one thing) onto a **Recognised Internal Description** via an LLM classifier, persisted in the `landlord_*_overrides` table (`source=classifier`) as a reviewed cache. Four vocabularies are kept **distinct** and must not be conflated: a **Landlord Description** (unbounded input); a **Recognised Internal Description** (the closed target taxonomy — e.g. a `MainHeatingSystemType` archetype — each binding to a Simulation Overlay); a **Lodged Description** (the gov-EPC `main_heating[].description` rendering, e.g. "Room heaters, electric" — only an example of which system *types* occur, never a map key); and the **SAP main heating code** (Table 4a/4b, what the calculator consumes). The classifier maps Landlord → Recognised Internal → SAP code. When it cannot confidently place the text it emits **`None`** (no overlay → the lodged EPC stands, surfaced to the user as "no suitable match"), **never the nearest wrong archetype** — the target taxonomy must be complete enough that a real system always has a correct home, so the classifier never overflows into a garbage-drawer archetype (ADR-0041). + +**Heating Companion Set**: +The coherent SAP inputs a **main heating system** override drags alongside the **SAP main heating code** so the **Effective EPC** reads as one internally-consistent system, not a hybrid of the new code and the *replaced* system's leftovers — heating **category** (SAP Table 4a group: gas→2, heat pump→4, network→6, storage→7, electric underfloor→8, warm air→9, room heater→10), **charge/heating control** (Table 4e group), **natural fuel**, and **meter** (see **Off-Peak Meter**). Companions divide by how firmly the archetype fixes them (ADR-0048): **category and control are archetype-forced** — always written, never inherited, because a wrong value silently mis-scores or mis-bills (a leftover storage **category 7** makes the Table 12a resolver bill peaky room heaters at the all-night rate; a leftover storage **control 2401** adds a +0.7 °C Table-4e penalty a room heater should not carry). **Fuel and meter defer** only where multiple values are genuinely coherent — fuel for an ambiguous carrier (community heating: gas CHP / biomass / waste heat), meter for a meter-flexible system (room heaters run on either; screed underfloor per ADR-0046) — while a meter-*locked* system still forces (storage/CPSU/HHRSH→Dual, non-electric→Single, ADR-0035). Because the overlay composes last-wins, an **unset (`None`)** forced companion is *inherited from the replaced system*, not cleared — so an archetype the overlay cannot yet fully companion (heat pump / community / underfloor / electric boiler control defaults are unmapped) is **logged as an error and continues** (log-not-raise, matching `flag_fuel_mismatch`), making the gap visible for review rather than shipping a silently-incoherent cert; the intended end-state is to fill each and flip the log to a raise. +_Avoid_: coherent companions (informal), dragged fields, heating defaults _Avoid_: "the LLM mapper is unreliable" (the failure mode is a too-small target taxonomy, not LLM language ability); conflating the landlord input vocabulary with the gov-EPC lodged rendering or the RdSAP entry-tool catalogue; treating a deterministic dict as a *replacement* for the LLM rather than a reviewed cache of its output **Lodgement Sentinels (ND / NI / AB)**: diff --git a/docs/adr/0048-heating-override-forces-category-and-control-defers-fuel-and-meter.md b/docs/adr/0048-heating-override-forces-category-and-control-defers-fuel-and-meter.md new file mode 100644 index 000000000..5b2a1870f --- /dev/null +++ b/docs/adr/0048-heating-override-forces-category-and-control-defers-fuel-and-meter.md @@ -0,0 +1,132 @@ +# A system-replacing heating override forces category and control for coherence, and defers fuel and meter where multiple values are valid + +## Status + +accepted + +## Context + +A **Landlord Override** naming a main heating system resolves to a SAP Table 4a +code, and `main_heating_system_overlay` synthesises the **coherent companions** +that code implies (ADR-0035): heating category, charge control, natural fuel, +meter. The overlay is applied over the lodged cert by last-wins composition, so a +companion the overlay leaves **unset (`None`)** is *inherited from the replaced +system* — not cleared. + +That inheritance is a silent mis-rating when the archetype genuinely determines +the companion. A portfolio-796 audit found the case end-to-end on **86+ +properties**: a lodged **slimline storage heater** (SAP 402, category 7, control +2401, off-peak) overridden to **"Electric room heaters"** (SAP 691). The overlay +stamped code 691, fuel, and a Dual meter — but `_category_for(691)` and +`_control_for(691)` both returned `None`, because their room-heater branch keyed +on `_CATEGORY_10_ROOM_HEATER_CODES`, a set that held only the *fuel-burning* +(gas/oil/solid) room heaters and **excluded electric 691–701** despite electric +room heaters also being Table 4a **Category 10**. + +Two independent mis-ratings followed from the surviving storage companions: + +1. **Category 7 survived.** The SAP 10.2 Table 12a resolver keys on category + first, read `OTHER_STORAGE_HEATERS`, and — with the dwelling on the §12 Rule 3 + 10-hour tariff — hit `(OTHER_STORAGE_HEATERS, TEN_HOUR)`, a combination the + Grid-1 table does not carry, so it fell to the all-low-rate fallback. The + peaky room heaters were billed **100% at the night rate** — the precise + "all-low over-credit" the overlay's own Dual-meter comment claims to avoid. + Effect: baseline SAP over-rated **64.1 vs the spec-correct 56.4**; the HHRSH + upgrade measure showed a **negative** bill saving (−£13/yr) because the + baseline it was compared against was itself under-billed. +2. **Control 2401 survived.** `main_heating_control` fed Table 4e as the storage + **manual charge control → +0.7 °C** mean-internal-temperature adjustment — the + largest in the table — riding on a direct-acting room heater, which should + carry the Group 6 room-heater control **2601 → +0.3 °C**. + +The companions are **not uniform** in how strongly the archetype determines +them, which is the crux of the decision: + +- **Category is deterministic** — SAP Table 4a assigns exactly one category per + code (gas→2, heat pump→4, network→6, storage→7, **electric underfloor→8**, + warm-air→9, **room heater→10**). A `None` category is never valid. +- **Control is an assumption but always archetype-supplied** — the Table 4e + *Group* is fixed by category; the specific conservative default within the + group is a modelling choice (storage→manual 2401, HHRSH→2404 per + [ADR-0044](0044-hhrsh-baseline-archetype-drags-its-intrinsic-controls.md), + room heater→2601, gas boiler→full controls). It is never "inherit the replaced + system". +- **Fuel is sometimes genuinely ambiguous** — electric/gas/storage/heat-pump + archetypes pin their fuel, but **community heating** could be gas CHP, biomass, + or waste heat, so its fuel legitimately **defers** to a `main_fuel` override, + else the lodged value (ADR-0041 last-wins). +- **Meter is physics-locked for some systems, flexible for others** — storage / + CPSU / HHRSH **require** Dual (they charge overnight); non-electric systems are + stamped Single to stop an Economy-7 split bleeding onto a gas boiler + ([ADR-0035](0035-coherent-heating-system-synthesis.md)); screed underfloor + defers to the cert ([ADR-0046](0046-electric-underfloor-scored-by-its-own-codes-meter-deferred-when-tariff-ambiguous.md)). + +## Decision + +A system-replacing heating override must emit a **complete, coherent companion +set**. Companions split by whether the archetype *determines* the value: + +1. **Category and control are archetype-forced** — always written, never + inherited, because a wrong value mis-scores or mis-bills the cert. Electric + room heaters (Table 4a 691–701) join the Category-10 room-heater branch of + both `_category_for` (→ category **10**) and `_control_for` (→ control + **2601**, the Group 6 conservative no-thermostat default, matching the + gas/oil/solid siblings). Their fuel (electricity 29) and Dual meter were + already correct and are unchanged. + +2. **Fuel and meter defer where multiple values are coherent** — this is *not* + a gap. Fuel defers only for genuinely ambiguous carriers (community heating); + meter defers only for meter-flexible systems (room heaters run coherently on + either meter; screed underfloor per ADR-0046). Meter-locked systems still + force (storage/CPSU/HHRSH → Dual; non-electric → Single). + +3. **An incomplete companion set is logged, not raised (for now).** Where the + overlay cannot yet supply a confident category or control — heat pumps + (Group 2), community (Group 3), electric underfloor (Group 7), electric + boiler / CPSU (Group 1) — `main_heating_overlay_for` **logs an error** naming + the archetype and code and continues, matching the `flag_fuel_mismatch` + log-not-raise convention. Log-and-continue keeps a mid-portfolio run alive + and surfaces the gap (CloudWatch) for review, rather than turning a latent + inheritance bug into an outage. The intended end-state is to fill each + archetype's category/control with spec sight and then **flip the log to a + raise**, so the coherence invariant is enforced. + +Category expansion for the still-`None` archetypes (electric boiler/CPSU→2, +underfloor→8) is deterministic from Table 4a but **deferred** to its own change: +it flows into the category-keyed Table 12a resolver and needs a corpus check, so +it does not ride on the room-heater fix. + +## Consequences + +- The 86+ room-heater dwellings score against a correctly-billed baseline: the + space-heating high-rate fraction is the spec **0.50** (10-hour direct-acting), + not 0.0; baseline SAP corrects **64.1 → 56.4**; the HHRSH measure's bill saving + flips **−£13/yr → +£235/yr** (property 710788, uprn 22003310, scenario 1268). +- The `refetch_solar`-corrected portfolio's `negative-bill-savings` audit group + loses its ~86-property HHRSH-on-room-heater cluster after re-model. +- The overlay now emits a visible error for any archetype it cannot fully + companion — a standing signal (wire a CloudWatch metric filter on the log + string) for which control default to fill next. +- Extends [ADR-0035](0035-coherent-heating-system-synthesis.md) (companions drag + from the code) and [ADR-0041](0041-landlord-heating-classification-targets-a-complete-modellable-taxonomy.md) + (complete taxonomy); sits beside + [ADR-0044](0044-hhrsh-baseline-archetype-drags-its-intrinsic-controls.md) + (a control named by the archetype) and + [ADR-0046](0046-electric-underfloor-scored-by-its-own-codes-meter-deferred-when-tariff-ambiguous.md) + (meter deferred where the tariff is ambiguous). + +### Alternatives rejected + +- **Make every companion total (force fuel and meter too).** Rejected: it breaks + the deliberate deferrals — community-heating fuel (ambiguous carrier) and the + ADR-0046 screed-underfloor meter — whose `None` is a load-bearing "defer to the + cert/override" signal, not a gap. +- **Fix the Table 12a resolver to prefer the SAP code over a stale category.** + A sound defence-in-depth follow-up, but it treats the symptom; the overlay + emitting an incoherent cert is the root cause, and category/control coherence + must hold for every consumer (predicted EPCs, raw lodged certs), not only the + billing resolver. +- **Raise on an incomplete companion set now.** Rejected for this change: heat + pump / community / underfloor overrides model today (by luck of inheritance), + so an immediate raise is a blast-radius change mid-campaign. Log now, raise once + the common archetypes are filled.