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Cohort residual slice 11: Simplified Type 1 RR geometry — _part_geometry + heat_transmission
Implements RdSAP10 §3.9.1 Simplified Type 1 (True Room-in-Roof, no
common walls):
A_RR = 12.5 × √(A_RR_floor / 1.5)
When the cert lodges only a `SapRoomInRoof(floor_area, construction_
age_band)` (no gable / party / sheltered / connected wall lengths),
ΣA_RR_gable/other = 0 → A_RR_final = A_RR, treated as timber-framed
roof structure with U from Table 18 col (4) "Room-in-roof, all elements".
The storey-below roof area (§3.8) is deducted by A_RR_floor per §3.9.
Changes:
- `_part_geometry`: returns new keys `rr_floor_area_m2` and
`rr_simplified_a_rr_m2`; existing `top_floor_area_m2` now subtracts
`rr_floor_area_m2` (the §3.9 deduction).
- Main loop: `roof += U_RR × A_RR` where U_RR is from
`u_rr_default_all_elements(country, rir.construction_age_band)`.
A_RR also joins the (31) external-area total for thermal-bridging.
Test: synthetic 2-storey + RR (15 m² floor) at age B → roof_w_per_k
math closes at abs=0.001 vs hand-computed 100.92 W/K.
Cohort impact (post-slice-11 vs post-slice-8):
- 000474, 000490 unchanged at Δ=0 ✓
- 000480: Δ=+12 → +4 (RR Simplified resolved most of the gap)
- 000487: Δ=+11 → +3 (same)
- 000516: Δ=+12 → +4 (same)
- 000477: Δ=+2 → −6 (overshoot — the U985 PDF uses detailed §3.10
per-surface RR lodgement; Simplified Type 1 at U=2.30 is too high
for an RR with measured retrofit insulation. Closes once Detailed
lands + 000477 fixture upgrades to detailed lodgement, slice 14.)
Reference: RdSAP 10 (10-06-2025) §3.9.1 page 21-22; Table 18 page 45.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
This commit is contained in:
Khalim Conn-Kowlessar
parent
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2 changed files with 103 additions and 3 deletions
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@ -56,9 +56,11 @@ from domain.ml.rdsap_uvalues import (
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u_floor,
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u_party_wall,
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u_roof,
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u_rr_default_all_elements,
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u_wall,
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u_window,
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)
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from math import sqrt
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_WALL_INSULATION_NONE: Final[int] = 4
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@ -147,6 +149,8 @@ def _part_geometry(part: SapBuildingPart) -> dict[str, float]:
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"top_floor_area_m2": 0.0,
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"gross_wall_area_m2": 0.0,
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"party_wall_area_m2": 0.0,
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"rr_floor_area_m2": 0.0,
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"rr_simplified_a_rr_m2": 0.0,
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}
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fds = list(part.sap_floor_dimensions)
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ground = next((fd for fd in fds if fd.floor == 0), fds[0])
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@ -165,11 +169,28 @@ def _part_geometry(part: SapBuildingPart) -> dict[str, float]:
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(fd.party_wall_length_m or 0.0) * (fd.room_height_m or _DEFAULT_STOREY_HEIGHT_M)
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for fd in fds
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)
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# RdSAP10 §3.9.1 Simplified Type 1 (True Room-in-Roof): when an RR is
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# lodged with only its floor area (no gable/party/sheltered/connected
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# wall lengths), the spec's empirical formula treats it as one chunk
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# of timber-framed roof structure of area A_RR = 12.5 × √(A_RR_floor
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# / 1.5). The storey-below roof area (§3.8) is deducted by A_RR_floor
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# — the regular roof "becomes" the residual footprint not under the
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# RR. Type 2 (common walls < 1.8m) and the Detailed §3.10 path are
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# additive on top — they decompose A_RR into per-surface areas with
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# their own U-values, deducted from A_RR_final per step e.
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rr_floor_area = 0.0
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rr_a_rr = 0.0
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rir = part.sap_room_in_roof
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if rir is not None and rir.floor_area > 0:
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rr_floor_area = float(rir.floor_area)
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rr_a_rr = 12.5 * sqrt(rr_floor_area / 1.5)
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return {
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"ground_floor_area_m2": ground.total_floor_area_m2 or 0.0,
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"top_floor_area_m2": top.total_floor_area_m2 or 0.0,
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"top_floor_area_m2": max(0.0, (top.total_floor_area_m2 or 0.0) - rr_floor_area),
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"gross_wall_area_m2": gross_wall,
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"party_wall_area_m2": party_wall,
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"rr_floor_area_m2": rr_floor_area,
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"rr_simplified_a_rr_m2": rr_a_rr,
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}
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@ -328,6 +349,21 @@ def heat_transmission_from_cert(
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walls += uw * main_wall_area + alt_walls_contribution
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roof += ur * roof_area
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# RdSAP10 §3.9.1 Simplified RR contribution. A_RR is treated as
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# timber-framed roof structure with U from Table 18 column (4)
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# "Room-in-roof, all elements" (the as-built / unknown default
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# per footnote (1)). The age band lives on the SapRoomInRoof, not
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# the SapBuildingPart, so we read it from there. Lines under (30)
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# in the U985 worksheet — same line ref as the regular roof, so
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# we fold the contribution into roof_w_per_k.
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rr_a_rr = geom["rr_simplified_a_rr_m2"]
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if rr_a_rr > 0:
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rir = part.sap_room_in_roof
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assert rir is not None # rr_a_rr > 0 ⇒ rir present per _part_geometry
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u_rr = u_rr_default_all_elements(
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country=country, age_band=rir.construction_age_band,
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)
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roof += u_rr * rr_a_rr
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floor += uf * floor_area_total
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party += upw * party_area
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windows += window_u * w_area
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@ -335,9 +371,11 @@ def heat_transmission_from_cert(
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# (31) — total external element area used by both the worksheet
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# readout and the (36) thermal-bridging multiplier. Excludes the
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# party wall (party walls have their own line (32)) per RdSAP
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# §5.15: bridging applies to *exposed* area only.
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# §5.15: bridging applies to *exposed* area only. RR area joins
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# the external surfaces per the spec — A_RR contributes to (31)
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# alongside walls + roof + floor + openings.
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part_external_area = (
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main_wall_area + alt_walls_total_area + roof_area + floor_area_total + w_area + d_area
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main_wall_area + alt_walls_total_area + roof_area + floor_area_total + w_area + d_area + rr_a_rr
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)
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total_external_area += part_external_area
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bridging += y * part_external_area
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@ -21,6 +21,7 @@ from datatypes.epc.domain.epc_property_data import (
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BuildingPartIdentifier,
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EnergyElement,
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SapAlternativeWall,
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SapRoomInRoof,
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)
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from domain.ml.tests._fixtures import (
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@ -1306,3 +1307,64 @@ def test_section_3_partial_match_against_elmhurst_worksheet(fixture: ModuleType)
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# (gap #1). Non-RR fixtures get exact (31) + (36) asserted by the
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# dedicated `test_section_3_non_rr_line_31_and_36_match_elmhurst_worksheet`.
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assert result.total_external_element_area_m2 > 0
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def test_room_in_roof_simplified_type_1_adds_a_rr_timber_framed_area_to_roof_w_per_k() -> None:
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"""RdSAP10 §3.9.1 Simplified Type 1 (True Room-in-Roof, no common
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walls). Formula (page 22 step d): A_RR = 12.5 × √(A_RR_floor / 1.5);
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this area is treated as timber-framed construction and assigned a
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U-value from Table 18 column (4) "Room-in-roof, all elements" by age
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band when no gable / party / sheltered / connected wall lengths are
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lodged (ΣA_RR_gable/other = 0 → A_RR_final = A_RR).
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Also (§3.9 page 21): A_RR_floor is deducted from the storey-below
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roof area determined by §3.8 (which takes the greatest floor area
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across levels).
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Synthetic dwelling for arithmetic clarity:
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- 2 storeys × 40 m² each → §3.8 roof area = 40
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- RR floor area = 15 m²
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- §3.9 deducted top-floor roof area = 40 − 15 = 25 m²
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- A_RR = 12.5 × √(15 / 1.5) = 12.5 × √10 ≈ 39.5285 m²
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- Age band B → U_roof (Table 18 col 1) = 0.40; U_RR (Table 18
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col 4 "as built") = 2.30.
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- roof_w_per_k = 25 × 0.40 + 39.5285 × 2.30 = 10.00 + 90.9156
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= 100.9156 W/K.
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"""
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# Arrange
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import math
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main = make_building_part(
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identifier=BuildingPartIdentifier.MAIN,
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construction_age_band="B",
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wall_construction=3,
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wall_insulation_type=4,
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party_wall_construction=1,
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roof_construction=4,
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floor_dimensions=[
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make_floor_dimension(
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total_floor_area_m2=40.0, room_height_m=2.5,
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heat_loss_perimeter_m=20.0, party_wall_length_m=0.0, floor=0,
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),
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make_floor_dimension(
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total_floor_area_m2=40.0, room_height_m=2.5,
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heat_loss_perimeter_m=20.0, party_wall_length_m=0.0, floor=1,
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),
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],
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sap_room_in_roof=SapRoomInRoof(floor_area=15.0, construction_age_band="B"),
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)
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epc = make_minimal_sap10_epc(
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total_floor_area_m2=95.0, # 40 + 40 + 15
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habitable_rooms_count=5,
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country_code="ENG",
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sap_building_parts=[main],
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)
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# Act
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result = heat_transmission_from_cert(
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epc, window_total_area_m2=0.0, window_avg_u_value=None, door_count=0,
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)
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# Assert
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a_rr = 12.5 * math.sqrt(15.0 / 1.5)
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expected_roof_w_per_k = (40.0 - 15.0) * 0.40 + a_rr * 2.30
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assert result.roof_w_per_k == pytest.approx(expected_roof_w_per_k, abs=0.001)
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