Record flat-roof-thickness and glazing-reconcile decisions (ADR 0041/0042)

ADR-0041: flat roofs ARE scored by insulation thickness via RdSAP Table 16
col (1) ('joists at ceiling level and flat roof'); the RoofType taxonomy lacks
flat-thickness members so the depth is discarded — fix needs new FLAT_*MM members
(FE-owned pgEnum). ADR-0042: a landlord glazing override reconciles against the
cert's per-window sap_windows composition rather than flattening every window to
one type; mixed-and-close defers to the cert, mixed-and-far is flagged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/adr/0041-flat-roofs-scored-by-insulation-thickness.md

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+# Flat roofs are scored by insulation thickness (RdSAP Table 16 col 1), not the age-band default
+
+## Context
+
+A **Landlord Override** naming a flat roof with a known insulation depth (`flat: 50mm` / `100mm` / `150mm`) is classified to the canonical `RoofType` value `"Flat, insulated (assumed)"`, which the roof **Simulation Overlay** resolves to `roof_construction_type='Flat'` with **no thickness**. The calculator then takes the U-value from the flat age-band default (`_FLAT_ROOF_BY_AGE`, RdSAP Table 18 column (3)). The stated depth is **discarded** — ~102 `property_overrides` rows.
+
+The overlay's own comment asserted *"No flat RoofType value carries an explicit mm depth"*. That is a **taxonomy artefact, not a truth about the data**: the `RoofType` enum has flat members only for insulation *state* (`FLAT_INSULATED / _ASSUMED / LIMITED / NO_INSULATION`) and **no flat-thickness members** — whereas pitched has the full `PITCHED_LOFT_12MM … 400MM` ladder. So a flat depth has nowhere to land and is lost at **classification**, before the overlay ever runs.
+
+Reviewing the **RdSAP 10 Specification (10-06-2025)** during grilling (issue #1361 override audit / #1376) settled the domain fact: **Table 16** ("Roof U-values when loft insulation thickness is known"), **column (1)**, is headed *"Insulation at joists at ceiling level **and flat roof**"*. A flat roof **is** scored by thickness — 50 mm → 0.68, 100 mm → 0.40, 150 mm → 0.30. Table 18 (the age-band default) is explicitly only the fallback *"used when thickness of insulation cannot be determined"*. The earlier assumption that flat roofs are age-band-only was wrong.
+
+The calculator already implements this correctly: `u_roof` routes a flat roof **with** a thickness through `_ROOF_BY_THICKNESS` (which *is* Table 16 col (1)). So a flat roof given its depth scores right today — the only defect is that the depth never reaches the calculator, because the taxonomy can't carry it.
+
+This is the opposite of the wall / flat "as built (assumed)" cases (ADR-0033), where **no** real datum exists and the age band is the correct lever. Here a **real measurement** exists and RdSAP scores it.
+
+## Decision
+
+Make a flat roof's known insulation thickness first-class, so it reaches Table 16 col (1):
+
+- Add **flat-thickness members** to the `RoofType` taxonomy — `FLAT_12MM … FLAT_400_PLUS_MM` (values like `"Flat, 150 mm insulation"` — **not** "loft"; a flat roof has no loft). Minimum set for today's data: 50, 100, 150; the full ladder mirrors the pitched members for symmetry.
+- The roof **Simulation Overlay** emits `roof_insulation_thickness` for a flat roof with a known depth (reusing the existing mm regex), alongside `roof_construction_type='Flat'`, so `u_roof` reaches Table 16 col (1) instead of the age-band default.
+- **Reclassify** the existing `flat: Nmm` rows off `"Flat, insulated (assumed)"` onto the new members.
+- Correct the misleading overlay comment.
+
+The flat/pitched distinction is retained even though Table 16 col (1) gives the same U at a given thickness for both — it stays load-bearing for non-U concerns (measure eligibility, shape), so flat depths are **not** collapsed onto the pitched members.
+
+## Consequences
+
+- ~102 flat-roof properties re-score from the age-band default to their true thickness-based U-value — **both directions** (a newer-band flat roof with 150 mm improves; an old-band flat with 50 mm may worsen relative to its default).
+- **Cross-repo (FE-owned pgEnum, Dan).** The `RoofType` `value` column is a Drizzle-owned Postgres enum (see `main-heating-system-pgenum-is-fe-owned`; PR #1361 Class A/B). The new members must be added to the pgEnum by the FE owner before the classifier-cache `value` writes; the `property_overrides` (TEXT) reclassify is immediate. So this is an **enum-dependent slice**, grouped with the other new-archetype slices of #1376 — not the no-enum roof/glazing resolver slice.
+- The reclassify follows the established one-time-script shape (dry-run default, `--apply` in a transaction, idempotent), and surfaces any members the live enum does not yet carry as deferred, exactly as Class A did.

docs/adr/0042-glazing-override-reconciles-against-cert-composition.md

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+# Landlord glazing override reconciles against the cert's per-window composition, not a whole-dwelling type
+
+## Context
+
+A **Landlord Override** for glazing is a whole-dwelling categorical (`GlazingType` — Single / Double pre- and post-2002 / Triple / Unknown). The glazing **Simulation Overlay** resolves it to one SAP10 `glazing_type` code, and `_fold_glazing` overwrites **every** window's `glazing_type` (and clears its lodged U-/g-value) — flattening the cert to a single type.
+
+The landlord descriptions are frequently **aggregate splits** ("40% double, 60% single"), and the LLM classifier collapses *any-double-present* to `"Double glazing"`. So ~319 `property_overrides` rows describing a **single-dominant** mix are scored as **fully double-glazed** — a material over-credit to the window U-values, hence to SAP.
+
+The Effective EPC already carries **per-window glazing**: `sap_windows`, each with its own `glazing_type` **and** `window_width`×`window_height` (so area is derivable), plus the dwelling-level `multiple_glazed_proportion`. This is **more granular** than any whole-dwelling summary, and a whole-dwelling percentage **cannot be faithfully assigned to specific windows** — "which windows are the single ones" is unknowable from an aggregate. `_fold_glazing` already holds the EPC at apply time, so the per-window data is available where the override is applied.
+
+Fixing this by "dominant type wins" would still **clobber real per-window variation** (a 60/40 dwelling flattened to one type). The faithful move is to treat the cert's per-window data as **authoritative** and the landlord aggregate as a **check** on it — the descriptions are, after all, aggregations of the same per-window split the cert records.
+
+## Decision
+
+The landlord glazing override **reconciles against the cert's per-window composition** instead of imposing a whole-dwelling type.
+
+- **Classifier emits a proportion, not just a dominant type.** The asserted glazing **proportion** (e.g. multiple-glazed %) is extracted by the **LLM** — which is there precisely because landlord inputs vary; we do **not** hard-parse one string format.
+- **Compute the cert's actual composition** from `sap_windows`, **area-weighted** by window (bigger windows dominate the dwelling U-window).
+- **Reconcile in `_fold_glazing`** (it holds the EPC), three outcomes:
+  - **Uniform assertion (~100% one type)** → apply the blanket type. Unambiguous, and a real correction (e.g. a full reglaze). Unchanged from today for clean cases.
+  - **Mixed, proportion within tolerance of the cert** → **no-op**. The cert already reflects it, per-window and more precisely — leave the better data alone.
+  - **Mixed, proportion materially different from the cert** → **no-op + flag**. The landlord genuinely disagrees, but per-window assignment is unknowable, so **do not fabricate a split** — surface it for review.
+- **Tolerance** is a tunable band on the area-weighted multiple-glazed %, pinned against the real distribution, not guessed.
+
+## Consequences
+
+- The ~319 over-credited rows stop being flattened to double; a mix that matches the cert is left on its per-window data, and a clean uniform reglaze still applies.
+- **No new enum.** A no-op reconciliation leaves the cert glazing untouched (as `Unknown` already does). But it needs a **classifier-output change** (emit a proportion) **plus** the reconcile in the **apply seam** (`_fold_glazing`) — so it is its **own slice**, distinct from the no-enum roof party-ceiling fix that ships first.
+- Genuine landlord-vs-cert glazing disagreements are **surfaced** rather than silently trusted (old behaviour: flatten to double) or silently overwritten.
+- **Alternatives rejected.** *Dominant type wins* — still clobbers per-window variation. *Carry a full landlord composition to re-derive per-window types* — per-window assignment from an aggregate is unknowable; we decline to fabricate it. *Deterministic regex of "X% double, Y% single"* — brittle against varied input, which is the LLM's job.
+- Pairs with the per-window fidelity the calculator already relies on: the reconciliation is only correct on a faithful Effective EPC whose `sap_windows` round-trip (cf. ADR-0040).