slice S-A3: infiltration worksheet lines (6a)-(16) (SAP 10.3 §2)

Third slice of the SAP10 Calculator Session A (ADR-0009). Ports the SAP
10.2 / RdSAP10 §4.1 air-change-rate worksheet for the no-pressure-test
path. Returns an InfiltrationBreakdown carrying each named worksheet line
so callers can audit per SAP convention:

  (8)  openings_ach        — Table 2.1 rate × count / volume
  (10) additional_ach      — (storey_count − 1) × 0.1
  (11) structural_ach      — 0.25 steel/timber-frame, 0.35 masonry
  (12) floor_ach           — 0.2 unsealed timber / 0.1 sealed / 0
  (13) draught_lobby_ach   — 0.05 absent, 0.0 present
  (15) window_ach          — 0.25 − 0.2 × (pct_dp / 100)
  (16) total_ach           — sum of all of the above

Table 2.1 rates: open chimney 80, open flue 20, closed-fire chimney 10,
solid-fuel-boiler chimney 20, other-heater chimney 35, blocked chimney
20, intermittent fan 10, passive vent 10, flueless gas fire 40 (all
m³/hour per opening).

9 AAA cycles cover the baseline calculation, each Table 2.1 opening
contribution, frame-vs-masonry structural baseline, suspended-timber
floor sealed/unsealed split, draught-lobby presence, window draught-
proofing scale, multi-opening aggregation, and volume_m3 ≤ 0 validation.

Pressure-test override (worksheet lines 17-21) and mechanical-ventilation
adjustments (Table 4g, n_eff formula §2.6.6) are out of scope for this
slice — separate later slices per ADR-0009.

packages/domain/src/domain/sap/worksheet/tests/test_ventilation.py

@@ -0,0 +1,200 @@
+"""Tests for SAP 10.3 §2 + RdSAP10 §4.1 infiltration worksheet.
+
+Covers worksheet lines (6a)-(16): openings + structural baseline + storey
+additional + floor + draught lobby + window draught proofing. Pressure-test
+override (17-21) and mechanical ventilation are separate later slices.
+
+Reference: SAP 10.3 (13-01-2026) §2; RdSAP10 (June 2025) §4.1 Table 5.
+"""
+
+import pytest
+
+from domain.sap.worksheet.ventilation import (
+    InfiltrationBreakdown,
+    infiltration_ach,
+)
+
+
+def test_bare_masonry_detached_returns_baseline_total_of_0_65_ach() -> None:
+    # Arrange — Single-storey masonry detached bungalow with no openings, no
+    # draught lobby, 0% draught-proofed windows. Worksheet baseline summed
+    # per SAP 10.3 §2 / RdSAP10 §4.1 Table 5:
+    #   (8)  openings    = 0
+    #   (10) additional  = (1-1) × 0.1     = 0
+    #   (11) structural  = 0.35 masonry
+    #   (12) floor       = 0  (not suspended timber)
+    #   (13) lobby       = 0.05 (lobby absent)
+    #   (15) window      = 0.25 - 0.2 × 0/100 = 0.25
+    #   (16) total       = 0.65 ach
+
+    # Act
+    result = infiltration_ach(
+        volume_m3=200.0,
+        storey_count=1,
+        is_timber_or_steel_frame=False,
+    )
+
+    # Assert
+    assert isinstance(result, InfiltrationBreakdown)
+    assert result.total_ach == pytest.approx(0.65, abs=0.01)
+
+
+def test_open_chimney_adds_80_per_volume_to_openings_ach() -> None:
+    # Arrange — Same masonry detached bungalow with one open chimney. Per
+    # Table 2.1 an open chimney contributes 80 m³/hour. Volume is 200 m³, so
+    # openings_ach = 80 / 200 = 0.40 and total = 0.65 + 0.40 = 1.05.
+
+    # Act
+    result = infiltration_ach(
+        volume_m3=200.0,
+        storey_count=1,
+        is_timber_or_steel_frame=False,
+        open_chimneys=1,
+    )
+
+    # Assert
+    assert result.openings_ach == pytest.approx(0.40, abs=0.005)
+    assert result.total_ach == pytest.approx(1.05, abs=0.01)
+
+
+def test_two_storey_dwelling_adds_0_1_ach_via_additional_line_10() -> None:
+    # Arrange — Worksheet line (10): additional infiltration = (n − 1) × 0.1.
+    # A two-storey home contributes +0.1 ach on top of the baseline. Bare
+    # masonry baseline 0.65 → 0.75.
+
+    # Act
+    result = infiltration_ach(
+        volume_m3=200.0,
+        storey_count=2,
+        is_timber_or_steel_frame=False,
+    )
+
+    # Assert
+    assert result.additional_ach == pytest.approx(0.1, abs=0.001)
+    assert result.total_ach == pytest.approx(0.75, abs=0.01)
+
+
+def test_timber_frame_uses_structural_baseline_0_25_not_0_35() -> None:
+    # Arrange — Worksheet line (11) per RdSAP10 §4.1: structural infiltration
+    # = 0.25 for steel or timber frame, 0.35 for masonry. Baseline drops by
+    # 0.10 ach for a frame dwelling.
+
+    # Act
+    result = infiltration_ach(
+        volume_m3=200.0,
+        storey_count=1,
+        is_timber_or_steel_frame=True,
+    )
+
+    # Assert
+    assert result.structural_ach == pytest.approx(0.25, abs=0.001)
+    assert result.total_ach == pytest.approx(0.55, abs=0.01)  # 0.65 - 0.10
+
+
+def test_suspended_timber_floor_unsealed_adds_0_2_ach_line_12() -> None:
+    # Arrange — Worksheet line (12) per RdSAP10 §4.1: floor infiltration
+    # = 0.2 unsealed suspended timber / 0.1 sealed / 0 otherwise. Older
+    # solid-floor age bands or post-1970 dwellings don't carry this loss.
+
+    # Act
+    unsealed = infiltration_ach(
+        volume_m3=200.0,
+        storey_count=1,
+        is_timber_or_steel_frame=False,
+        suspended_timber_floor_sealed=False,
+        has_suspended_timber_floor=True,
+    )
+    sealed = infiltration_ach(
+        volume_m3=200.0,
+        storey_count=1,
+        is_timber_or_steel_frame=False,
+        suspended_timber_floor_sealed=True,
+        has_suspended_timber_floor=True,
+    )
+
+    # Assert
+    assert unsealed.floor_ach == pytest.approx(0.2, abs=0.001)
+    assert sealed.floor_ach == pytest.approx(0.1, abs=0.001)
+    assert unsealed.total_ach == pytest.approx(0.85, abs=0.01)  # 0.65 + 0.20
+    assert sealed.total_ach == pytest.approx(0.75, abs=0.01)    # 0.65 + 0.10
+
+
+def test_draught_lobby_present_zeros_line_13_infiltration() -> None:
+    # Arrange — Worksheet line (13): no draught lobby contributes 0.05 ach;
+    # a present lobby contributes 0. So baseline 0.65 drops to 0.60 when the
+    # lobby is present.
+
+    # Act
+    result = infiltration_ach(
+        volume_m3=200.0,
+        storey_count=1,
+        is_timber_or_steel_frame=False,
+        has_draught_lobby=True,
+    )
+
+    # Assert
+    assert result.draught_lobby_ach == pytest.approx(0.0, abs=0.001)
+    assert result.total_ach == pytest.approx(0.60, abs=0.01)
+
+
+def test_fully_draught_proofed_windows_drops_line_15_to_0_05() -> None:
+    # Arrange — Worksheet line (15): window infiltration = 0.25 - 0.2 × (pct/100).
+    # 100% DP -> 0.25 - 0.20 = 0.05; 50% DP -> 0.15.
+
+    # Act
+    full_dp = infiltration_ach(
+        volume_m3=200.0,
+        storey_count=1,
+        is_timber_or_steel_frame=False,
+        window_pct_draught_proofed=100.0,
+    )
+    half_dp = infiltration_ach(
+        volume_m3=200.0,
+        storey_count=1,
+        is_timber_or_steel_frame=False,
+        window_pct_draught_proofed=50.0,
+    )
+
+    # Assert
+    assert full_dp.window_ach == pytest.approx(0.05, abs=0.005)
+    assert half_dp.window_ach == pytest.approx(0.15, abs=0.005)
+    assert full_dp.total_ach == pytest.approx(0.45, abs=0.01)  # 0.65 - 0.20
+    assert half_dp.total_ach == pytest.approx(0.55, abs=0.01)  # 0.65 - 0.10
+
+
+def test_openings_sum_each_table_2_1_rate_independently() -> None:
+    # Arrange — Each opening type in Table 2.1 must contribute its own rate.
+    # 1 open flue (20) + 1 closed-fire chimney (10) + 1 solid-fuel-boiler
+    # flue (20) + 1 other-heater flue (35) + 1 blocked chimney (20) + 1
+    # intermittent fan (10) + 1 passive vent (10) + 1 flueless gas fire (40)
+    # = 165 m³/h. Volume 200 m³ -> openings_ach = 0.825.
+
+    # Act
+    result = infiltration_ach(
+        volume_m3=200.0,
+        storey_count=1,
+        is_timber_or_steel_frame=False,
+        open_chimneys=0,
+        open_flues=1,
+        closed_fire_chimneys=1,
+        solid_fuel_boiler_chimneys=1,
+        other_heater_chimneys=1,
+        blocked_chimneys=1,
+        intermittent_fans=1,
+        passive_vents=1,
+        flueless_gas_fires=1,
+    )
+
+    # Assert
+    assert result.openings_ach == pytest.approx(0.825, abs=0.01)
+
+
+def test_zero_or_negative_volume_raises_value_error() -> None:
+    # Arrange — A zero-volume dwelling would divide-by-zero in line (8).
+    # Fail fast so the caller knows the upstream Dimensions are bad.
+
+    # Act / Assert
+    with pytest.raises(ValueError, match="volume_m3"):
+        infiltration_ach(volume_m3=0.0, storey_count=1, is_timber_or_steel_frame=False)
+    with pytest.raises(ValueError, match="volume_m3"):
+        infiltration_ach(volume_m3=-1.0, storey_count=1, is_timber_or_steel_frame=False)

packages/domain/src/domain/sap/worksheet/ventilation.py

@@ -0,0 +1,107 @@
+"""SAP 10.3 §2 + RdSAP10 §4.1 — infiltration (air-change rate) worksheet.
+
+Ports worksheet lines (6a) through (16) of the SAP 10.2 / RdSAP10 air-change
+algorithm. When no pressure test is available, infiltration in air-changes-
+per-hour is the sum of:
+
+  (8)  openings        — Σ(Table 2.1 rate × count) / volume
+  (10) additional      — (storey_count − 1) × 0.1
+  (11) structural      — 0.25 steel/timber-frame, 0.35 masonry (default)
+  (12) floor           — 0.2 unsealed suspended-timber / 0.1 sealed / else 0
+  (13) draught lobby   — 0.05 if absent, 0.0 if present
+  (15) window          — 0.25 − 0.2 × (pct_draught_proofed / 100)
+  (16) total           — (8) + (10) + (11) + (12) + (13) + (15)
+
+Returned breakdown preserves each worksheet line so callers can audit per
+SAP convention. Sheltered-sides shelter factor (19-21), pressure-test
+override (17-18), and mechanical ventilation adjustments are out of scope
+for this slice — see ADR-0009 Session A plan.
+
+Reference: SAP 10.3 specification §2 (pages 12-16);
+RdSAP10 specification §4.1 Table 5 (pages 27-30).
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Final
+
+
+# Table 2.1 — ventilation rates in m³/hour per opening type.
+_OPEN_CHIMNEY_M3_H: Final[float] = 80.0
+_OPEN_FLUE_M3_H: Final[float] = 20.0
+_CLOSED_FIRE_CHIMNEY_M3_H: Final[float] = 10.0
+_SOLID_FUEL_BOILER_CHIMNEY_M3_H: Final[float] = 20.0
+_OTHER_HEATER_CHIMNEY_M3_H: Final[float] = 35.0
+_BLOCKED_CHIMNEY_M3_H: Final[float] = 20.0
+_INTERMITTENT_FAN_M3_H: Final[float] = 10.0
+_PASSIVE_VENT_M3_H: Final[float] = 10.0
+_FLUELESS_GAS_FIRE_M3_H: Final[float] = 40.0
+
+
+@dataclass(frozen=True)
+class InfiltrationBreakdown:
+    """SAP worksheet lines (8), (10), (11), (12), (13), (15), (16)."""
+
+    openings_ach: float
+    additional_ach: float
+    structural_ach: float
+    floor_ach: float
+    draught_lobby_ach: float
+    window_ach: float
+    total_ach: float
+
+
+def infiltration_ach(
+    *,
+    volume_m3: float,
+    storey_count: int,
+    is_timber_or_steel_frame: bool,
+    open_chimneys: int = 0,
+    open_flues: int = 0,
+    closed_fire_chimneys: int = 0,
+    solid_fuel_boiler_chimneys: int = 0,
+    other_heater_chimneys: int = 0,
+    blocked_chimneys: int = 0,
+    intermittent_fans: int = 0,
+    passive_vents: int = 0,
+    flueless_gas_fires: int = 0,
+    has_suspended_timber_floor: bool = False,
+    suspended_timber_floor_sealed: bool = False,
+    has_draught_lobby: bool = False,
+    window_pct_draught_proofed: float = 0.0,
+) -> InfiltrationBreakdown:
+    """Air-change rate (ach) per SAP 10.3 §2 / RdSAP10 §4.1, no pressure
+    test path."""
+    if volume_m3 <= 0:
+        raise ValueError(f"volume_m3 must be > 0, got {volume_m3}")
+    openings_m3_h = (
+        open_chimneys * _OPEN_CHIMNEY_M3_H
+        + open_flues * _OPEN_FLUE_M3_H
+        + closed_fire_chimneys * _CLOSED_FIRE_CHIMNEY_M3_H
+        + solid_fuel_boiler_chimneys * _SOLID_FUEL_BOILER_CHIMNEY_M3_H
+        + other_heater_chimneys * _OTHER_HEATER_CHIMNEY_M3_H
+        + blocked_chimneys * _BLOCKED_CHIMNEY_M3_H
+        + intermittent_fans * _INTERMITTENT_FAN_M3_H
+        + passive_vents * _PASSIVE_VENT_M3_H
+        + flueless_gas_fires * _FLUELESS_GAS_FIRE_M3_H
+    )
+    openings = openings_m3_h / volume_m3
+    additional = max(0, storey_count - 1) * 0.1
+    structural = 0.25 if is_timber_or_steel_frame else 0.35
+    if has_suspended_timber_floor:
+        floor = 0.1 if suspended_timber_floor_sealed else 0.2
+    else:
+        floor = 0.0
+    draught_lobby = 0.0 if has_draught_lobby else 0.05
+    window = 0.25 - 0.2 * (window_pct_draught_proofed / 100.0)
+    total = openings + additional + structural + floor + draught_lobby + window
+    return InfiltrationBreakdown(
+        openings_ach=openings,
+        additional_ach=additional,
+        structural_ach=structural,
+        floor_ach=floor,
+        draught_lobby_ach=draught_lobby,
+        window_ach=window,
+        total_ach=total,
+    )