SAP 10.2 Table 3 (PDF p.160) verbatim:
Primary loss is set to zero for the following:
Electric immersion heater
Combi boiler ...
CPSU ...
Boiler and thermal store within a single casing
Separate boiler and thermal store connected by no more than 1.5
m of insulated pipework
Direct-acting electric boiler
Heat pump (...) with hot water vessel integral to package
The Elmhurst WHC=903 lodging signals exactly the first row: "HW from
a separate electric immersion heater" — the cylinder is heated by an
immersion element inside the tank, no primary pipework between any
heat generator and the cylinder. The rule is universal: regardless
of what main heating exists for space heating, electric immersion
means no primary circuit means no primary loss.
Pre-slice `_primary_loss_applies` only consulted `water_heating_code`
in the Table 4a wet-boiler branch (codes 151-161 / 191-196). The Cat
4 HP branch returned True unconditionally when no PCDB record was
lodged; the Cat 1/2 boiler branch returned True unconditionally; the
PCDB Table 322 + Table 4b non-PCDB branches likewise. For the
electric 2 corpus variant (sap_main_heating_code=524 Cat 5 warm-air
ASHP, main_heating_category=4 per Elmhurst mapper, no PCDB record,
WHC=903 + cylinder), the Cat-4 branch falsely returned True and the
cascade added ~510 kWh/yr primary loss to a system with no primary
circuit at all.
Per-line walk discipline applied: cascade `water_heating_from_cert`
output dump showed `primary_loss_monthly_kwh_annual = 509.98` while
worksheet (59)m = 0 every month → spec lookup found Table 3 verbatim
"Electric immersion heater" zero-loss line.
Adds `_WHC_ELECTRIC_IMMERSION: Final[int] = 903` constant + a
top-of-function `if water_heating_code == _WHC_ELECTRIC_IMMERSION:
return False` guard that fires before any of the system-type-keyed
branches.
Closures electric 2:
HW kWh 2849.22 → 2339.24 (matches worksheet (62)/(64) = 2384.12
within the residual ~45 kWh storage-loss gap)
ΔSAP −0.4584 → +0.8118 (cascade swung past the worksheet by +1.27
— the pre-slice 'near-correct' value was offsetting cascade bugs
per [[feedback-software-no-special-handling]]; the +0.81 residual
exposes a separate upstream gap to chase in a follow-up slice)
Δcost +£10.56 → −£18.71
ΔCO2 +47.89 → −7.21 kg
ΔPE +443.13 → −161.68 kWh
No regressions on the other 24 cohort variants — only electric 2 has
the (Cat 4 HP, no PCDB, WHC=903) combination in the corpus.
Extended handover suite: 900 pass / 0 fail (was 899 — +1 from the
new AAA test). Pyright net-zero (43 → 43).
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
5 certs in a 2026 API sample raised `KeyError: 'rr_common_wall_area_m2'`
and were blocked from computing. Root cause: `_part_geometry`'s early
return (taken when a building part lodges no sap_floor_dimensions —
e.g. a party-wall-only or RR-only extension as bp[0]) returned only 6 of
the 9 keys the full return exposes, omitting rr_common_wall_area_m2,
rr_gable_area_m2 and cantilever_floor_area_m2. The §3.9 RR contribution
block reads geom["rr_common_wall_area_m2"] / ["rr_gable_area_m2"] for
EVERY part, so the floorless part's truncated dict raised KeyError at
heat_transmission.py:974.
Fix: the early return now exposes all 9 keys, the three RR/cantilever
geometry values defaulting to 0.0 — correct, since a part with no floor
dimensions has no derivable RR shell or cantilever (no floor area).
Pure contract-completion bug; no spec/U-value change.
Regression test pins the invariant directly: a floorless part's
_part_geometry keys must equal a with-floors part's keys. Validated: all
5 certs now compute (4 within ~2 SAP of lodged; the 5th, 8536, has a
separate residual). §4 suite 2393 passed; heat_transmission.py pyright
unchanged at 12, test file at 71.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Slice 2b. Timber frame (wall_construction=5) takes internal wall insulation but
not external (not constructable — ADR-0019), so the generator offers IWI only.
Cascade pin: the IWI Option reproduces the re-lodged timber-frame after at
abs(diff) <= 1e-4 (general Table 6 insulation-thickness bucket, not the solid-
brick documentary path).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Slice 2a. New recommend_solid_wall emits one Main-wall Recommendation carrying
External + Internal wall-insulation Options for an uninsulated (wall_insulation
_type=4) solid-brick (wall_construction=3) main wall, each priced at the heat-
loss wall area. Cascade pin: the generator's EWI and IWI Options reproduce
their respective re-lodged afters at abs(diff) <= 1e-4.
Detection keys on wall_construction code, not description (ADR-0019 note
corrected): the Elmhurst ingestion path leaves walls[].description empty, so
the code is the only cross-path signal; codes 1-5 are consistent.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
above) → None
The 2026 sample lodges roof_construction=6 (1 cert, "Thatched, with
additional insulation") and =7 (6 certs, "(same dwelling above)" /
"(another dwelling above)"), both raising UnmappedApiCode and blocking
the cert. roof_construction_type is read ONLY for the §3 "sloping
ceiling" cos(30°) inclined-surface factor (Slice 89); the base roof
U-value comes from the global roofs[].description. Neither code is a
sloping ceiling:
- 6 = thatched — U set by the description, not this field;
- 7 = same/another dwelling above — an internal ceiling with no roof
heat loss (the roof-side analogue of floor_construction code 0,
governed by the roof_heat_loss / description path).
Map both to None: carries no information the cascade consumes here and
correctly avoids the cos(30°) false-trigger. Empirically inert and
validated — roof W/K is byte-identical whether 6/7 map to None or to an
explicit pitched string across all code-6/7 certs in the sample. 5 of
the 7 now compute (e.g. thatched cert 2276 SAP 62.8 vs lodged 63); the
other 2 also carry a gable_wall_type 2/3 raise (separate, worksheet-
backed slice).
Dict value type widened to Optional[str]. §4 suite 2392 passed; mapper.py
pyright unchanged at 32; new tests suppress reportPrivateUsage (net-zero).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Captures the grill-with-docs session for solid-wall insulation: CONTEXT.md
gains EWI/IWI Measure Types + the Wall Insulation Eligibility rule (+ a
flagged-ambiguity that the three planning flags stay distinct, never recollapsed
to legacy restricted_measures). ADR-0019 records the eligibility policy (cavity
-> cavity only; brick/system -> IWI+EWI; timber -> IWI only; cob/stone -> none;
conservation/flat block EWI, listed/heritage block both). ADR-0020 records
conservation/listed/heritage as three distinct Property attributes sourced by
extending the geospatial S3 repo (flags co-located with lat/long).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Slice 1 of solid-wall insulation. BuildingPartOverlay gains a
wall_insulation_thickness field; the generic applicator already folds it onto
SapBuildingPart by name. With wall_insulation_type=1 (EWI) / 3 (IWI) + 100 mm,
the calculator derives the post-insulation U-value (§5.8 documentary path,
λ=0.04 default) — and for IWI also lowers the thermal-mass parameter. Two new
Elmhurst before/after cascade pins (solid-brick EWI + IWI, cert 001431)
reproduce the re-lodged after at abs(diff) <= 1e-4 across SAP/CO2/PE.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
A 2026-register cert (4519-9056-4002-0222-4802) omits the top-level
post_town entirely (its town sits only in address_line_3 "BARNSTAPLE").
RdSapSchema21_0_x declares post_town as a required no-default field, so
from_dict raised "missing required field 'post_town'" and blocked the
whole cert from computing.
post_town is address metadata the SAP cascade never reads (no consumer
in domain/sap10_calculator/), so default an absent post_town to "" in a
from_api_response pre-processor (mirroring _normalize_shower_outlets) —
inert for the calculation, keeps the cert mappable. The schema dataclass
can't simply give post_town a default: it is a plain (non-kw_only)
dataclass with 57 required fields after post_town, so a mid-list default
would break field ordering.
Validated: cert 4519 now maps (post_town="") and computes SAP cont 74.68
vs lodged 75. §4 suite 2392 passed; mapper.py pyright unchanged at 32;
new tests suppress reportPrivateUsage (net-zero).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
The 2026 sample's second-largest mapper raise: 37 certs lodge
sap_floor_dimensions.floor_construction=0, which raised UnmappedApiCode
and blocked the cert. Code 0 is the "not recorded / not applicable"
sentinel — 33/37 pair it with floor_heat_loss=6 ("another dwelling
below", an upper-floor flat with no ground floor to describe); the rest
carry mixed Solid / unheated-space descriptions. There is no single
construction to assert.
Map code 0 → None, which defers to RdSAP 10 Table 19 ("where floor
construction is unknown" → age-band default) — identical to how an
unlodged floor_construction (the 993 None certs) is already handled, and
honest about the absence (cf. the no-misleading-insulation_type rule).
Empirically inert and validated: across all 37 code-0 certs the cascade
floor W/K is byte-identical whether code 0 maps to None or to an explicit
"Solid" string — the another-dwelling-below floors compute to 0.0 W/K
(handled via floor_heat_loss + property_type=Flat + floors[].description,
per the _API_FLOOR_HEAT_LOSS_TO_FLOOR_TYPE code-6 note), and the few
genuine ground/unheated floors hit the same age-band default either way.
All 37 now compute (were raising).
Dict value type widened to Optional[str] for the None entry; helper
already returns Optional[str]. §4 suite + schema-mapper tests green
(pre-existing test_total_floor_area failure unrelated); mapper.py pyright
unchanged at 32; new test suppresses reportPrivateUsage (net-zero).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
A random 1000-cert Jan–May 2026 EPB-register sample surfaced 53 certs
lodging sap_floor_dimensions.floor_construction=3, which raised
UnmappedApiCode and blocked the whole cert from computing (~44 of the
sample's mapper raises). RdSAP 10 field 3-1 "Floor construction"
enumerates the lowest-floor construction as solid / suspended timber /
suspended, not timber, and the spec's "Suspended not timber (structural
infiltration 0)" makes the split load-bearing.
Map code 3 to the canonical "Suspended, not timber" string (the same
value the site-notes mapper already emits — cross-mapper parity):
- u_floor takes the suspended BS EN ISO 13370 branch via the
"Suspended" prefix (_floor_is_suspended_from_description), and
- _has_suspended_timber_floor_per_spec's exact-match
`!= "Suspended timber"` gate correctly does NOT fire, so the §5 (12)
0.1/0.2 floor-infiltration adjustment is skipped (structural
infiltration 0) — exactly the spec rule for not-timber suspended.
Validated: all 5 sampled code-3 certs now compute (e.g.
0340-2877-5570-2606-5965 floor_construction_type="Suspended, not
timber", SAP cont 60.12 vs lodged 60). Confirmed against the cert's own
global floor descriptions ("Suspended, …", floor_heat_loss=7).
Code semantics established from the RdSAP 10 spec + the lodged certs'
human-readable floor descriptions (the EPB /api/codes endpoint carries
no floor_construction enum). §4 suite + schema-mapper tests green
(the pre-existing test_total_floor_area failure is unrelated). mapper.py
pyright unchanged at 32; new test suppresses reportPrivateUsage to keep
net-zero new errors.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Record S0380.218 shipped, bump HEAD/next-slice, note both certs are
0-residual cross-validated golden fixtures and flag the optional
Summary-path regression guard as the cheap follow-up.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
