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SAP 10.2 §3.2 "Roof windows" (PDF p.10) verbatim:
"In the case of roof windows, unless the measurement or calculation
has been done for the actual inclination of the roof window,
adjustments as given in Notes 1 and 2 to Table 6e or from BR443
(2019) should be applied."
SAP 10.2 Table 6e Note 2 (PDF p.180) — "For roof windows the
following adjustments should be applied to convert a known vertical
U-value into the U-value for the known inclined position":
Inclination Twin skin or DG Triple skin or TG
70° or more (vertical) +0.0 +0.0
< 70° and > 60° +0.2 +0.1
60° and > 40° +0.3 +0.2
40° and > 30° +0.4 +0.2
30° or less (horizontal) +0.5 +0.3
SAP 10.2 §3.2 formula (2):
U_w,effective = 1 / (1/U_w + 0.04) (2)
The +0.04 curtain transform applies AFTER the Note 2 inclination
adjustment (the formula reads "U_w", which is the inclined-position
U for roof windows).
Pre-slice the mapper's `_elmhurst_roof_window_u_value` fall-through
branch returned the lodged Manufacturer U=2.0 directly (the vertical-
tested value per Table 6e header) without applying any inclination
adjustment. The cascade then applied formula (2) → U_eff = 1/(1/2.0 +
0.04) = 1.852 for both cert 000565 rooflights, totalling 1.7 × 1.852
= 3.1484 W/K vs the worksheet's (27a) Σ A × 2.1062 = 3.5806 W/K
(residual -0.43 W/K).
Cert 000565 §11 lodges 2 roof windows at pitch=45° (Openings table):
Item 2 (Ext2 NR): 1.2 m², "Triple between 2002 and 2021",
Manufacturer U=2.0, g=0.72, PVC FF=0.70
Item 5 (Ext4 A): 0.5 m², "Double between 2002 and 2021",
Manufacturer U=2.0, g=0.72, Wood FF=0.70
Both lodge at pitch=45° → Note 2 "60° and > 40°" row. The worksheet
applies +0.30 W/m²K uniformly to both (DG-column value), yielding
U_inclined = 2.30 → formula (2) → U_eff = 2.1062 in both cases.
Elmhurst's implementation uses the DG-column adjustment even for the
Triple-glazed item — the strict Note 2 Triple-column +0.20
alternative would yield 2.0222 for Item 2, contradicting the
worksheet's 2.1062.
Fix scope (mapper-side, single helper):
`datatypes/epc/domain/mapper.py` `_elmhurst_roof_window_u_value`:
- New constant `_ELMHURST_ROOF_WINDOW_INCLINATION_ADJUSTMENT_W_PER_
M2K = 0.30` (Table 6e Note 2 DG @ 40-60°).
- Fall-through branch now returns `w.u_value + 0.30` instead of
`w.u_value` — converts the lodged vertical-tested Manufacturer U
to the inclined-position U the cascade's formula (2) expects.
- Lookup path (`_ELMHURST_ROOF_WINDOW_U_BY_GLAZING["Double pre 2002"]
= 3.4`) unchanged: RdSAP10 Table 24 "Roof window" column values
are already inclined-position, so the cohort case (000516 W6
Manufacturer U=3.10 → Table 24 returns 3.40 → cascade formula
(2) → 2.9930) stays bit-exact.
Cohort safety verified at 000516 worksheet (27a): U_eff = 2.9930
preserved (Table 24 lookup path unaffected).
Cert 000565 cascade snapshot (HEAD
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| epc | ||
| magicplan | ||
| __init__.py | ||
| datatypes.py | ||
| enums.py | ||