diff --git a/datatypes/epc/domain/mapper.py b/datatypes/epc/domain/mapper.py
index a699be4e..380192d3 100644
--- a/datatypes/epc/domain/mapper.py
+++ b/datatypes/epc/domain/mapper.py
@@ -6942,6 +6942,12 @@ _ELMHURST_GLAZING_LABEL_TO_SAP10: Dict[str, int] = {
     "Single glazing": 1,
     "Double pre 2002": 2,
     "Double between 2002 and 2021": 3,
+    # Year-truncated form of "Double between 2002 and 2021": the trailing
+    # "and 2021" wraps to an adjacent PDF table cell that the extractor
+    # joins away (same artifact as "Triple post or during" below). Same
+    # SAP 10.2 code 3 (DG 2002-2021) — surfaced on the simulated-case-46
+    # multi-attribute worksheet.
+    "Double between 2002": 3,
     "Double with unknown install date": 3,
     "Double with unknown 16 mm or install date more": 3,
     # Elmhurst §11 lodgement of RdSAP-21 schema row 7 "double, known
diff --git a/domain/sap10_calculator/calculator.py b/domain/sap10_calculator/calculator.py
index 11cecf73..fb859bf6 100644
--- a/domain/sap10_calculator/calculator.py
+++ b/domain/sap10_calculator/calculator.py
@@ -617,7 +617,13 @@ def calculate_sap_from_inputs(inputs: CalculatorInputs) -> SapResult:
         )
     ecf = energy_cost_factor(total_cost_gbp=total_cost, total_floor_area_m2=tfa)
     sap_int = sap_rating_integer(ecf=ecf)
-    sap_cont = sap_rating(ecf=ecf)
+    # SAP 10.2 §13 / RdSAP 10 §13: the SAP rating is floored at 1 ("if the
+    # result of the calculation is less than 1, the rating is 1"). Apply the
+    # same floor to the continuous value so it stays a valid rating — the
+    # un-rounded part is for sensitivity NEAR real ratings, not for emitting
+    # a physically impossible negative SAP on a degenerate dwelling (e.g. a
+    # cert lodged at the floor of 1). Mirrors `sap_rating_integer`'s max(1,…).
+    sap_cont = max(1.0, sap_rating(ecf=ecf))
     co2_factor = inputs.co2_factor_kg_per_kwh
     # Per-end-use effective CO2 factors (Table 12d monthly cascade for
     # electricity, annual for gas). cert_to_inputs supplies these from
diff --git a/domain/sap10_calculator/rdsap/cert_to_inputs.py b/domain/sap10_calculator/rdsap/cert_to_inputs.py
index cd146109..8227764b 100644
--- a/domain/sap10_calculator/rdsap/cert_to_inputs.py
+++ b/domain/sap10_calculator/rdsap/cert_to_inputs.py
@@ -2631,6 +2631,7 @@ def _secondary_fraction(
     main: Optional[MainHeatingDetail],
     secondary_heating_type: object,
     secondary_lodged: bool = False,
+    unheated_habitable_rooms: bool = False,
 ) -> float:
     """SAP 10.2 Table 11 lookup by main heating category, applied only
     when (a) the cert has a secondary system lodged OR (b) the main
@@ -2672,7 +2673,12 @@ def _secondary_fraction(
     code = main.sap_main_heating_code
     has_lodged_secondary = secondary_heating_type is not None or secondary_lodged
     force = code is not None and code in _FORCE_SECONDARY_FOR_MAIN_CODES
-    if not has_lodged_secondary and not force:
+    # SAP 10.2 Appendix A.2.2 — when the main system does not heat every
+    # habitable room, the unheated rooms are assumed to be served by a
+    # portable-electric secondary heater, so the Table 11 fraction is costed
+    # even with no lodged secondary (the secondary fuel/efficiency cascade
+    # already defaults to portable electric, code 693, when no code lodged).
+    if not has_lodged_secondary and not force and not unheated_habitable_rooms:
         return 0.0
     if (
         code is not None
@@ -2682,6 +2688,26 @@ def _secondary_fraction(
     return _secondary_heating_fraction_for_category(main.main_heating_category)
 
 
+def _has_unheated_habitable_rooms(epc: EpcPropertyData) -> bool:
+    """SAP 10.2 Appendix A.2.2 — the main heating system does not heat every
+    habitable room (heated rooms < habitable rooms), so the unheated rooms
+    take an assumed portable-electric secondary heater.
+
+    Prefers the lodged `any_unheated_rooms` flag (set on both the gov-API and
+    Elmhurst paths). Falls back to the heated/habitable room-count comparison
+    only when the heated count is a real positive value — a lodged
+    `heated_rooms_count == 0` is the "not provided" sentinel on the gov-API
+    path, not literally zero heated rooms, so it must not spuriously trigger
+    the assumed secondary."""
+    if epc.any_unheated_rooms is not None:
+        return epc.any_unheated_rooms
+    return (
+        epc.heated_rooms_count > 0
+        and epc.habitable_rooms_count > 0
+        and epc.heated_rooms_count < epc.habitable_rooms_count
+    )
+
+
 def _has_lodged_secondary_description(epc: EpcPropertyData) -> bool:
     """True when the cert lodges a secondary-heating DESCRIPTION (the
     gov-API path surfaces the secondary as `secondary_heating.description`,
@@ -4735,6 +4761,7 @@ def energy_requirements_section_from_cert(
         main,
         epc.sap_heating.secondary_heating_type if epc.sap_heating else None,
         secondary_lodged=_has_lodged_secondary_description(epc),
+        unheated_habitable_rooms=_has_unheated_habitable_rooms(epc),
     )
     # When no secondary system is lodged the worksheet displays (208) = 0;
     # the per-system fuel formula already collapses to 0 via fraction_201 = 0
@@ -4960,16 +4987,23 @@ def ventilation_from_cert(
     storeys = max(1, dim.storey_count)
     vc = _ventilation_counts(epc.sap_ventilation)
     sv = epc.sap_ventilation
-    # RdSAP 10 §4.1 Table 5 (PDF p.28) — extract-fans default when the
-    # lodged count is below the age-band minimum. The Elmhurst Summary
-    # renders "0" as the form for unknown; the worksheet applies the
-    # default via `max(lodged, table_5_default)`.
+    # RdSAP 10 §4.1 Table 5 (PDF p.28) — extract fans: "Number of extract
+    # fans if known; if number is unknown: [age-band default]." The default
+    # is an UNKNOWN-fallback, NOT a floor: a genuinely-lodged count is used
+    # as-is even when it is below the age-band default (e.g. a band H-M
+    # dwelling lodging 2 fans is NOT bumped to the 3-fan default). The
+    # Elmhurst Summary / RdSAP convention renders "0" as the form for
+    # unknown, so a lodged 0 falls back to the default; any positive count
+    # is taken literally. (Was `max(lodged, default)`, which over-applied
+    # the default as a minimum and over-counted ventilation.)
     age_band = _dwelling_age_band(epc) or ""
     is_park_home = (epc.property_type or "").strip().lower() == "park home"
     table_5_fan_default = _rdsap_extract_fans_default(
         age_band, epc.habitable_rooms_count, is_park_home=is_park_home,
     )
-    intermittent_fans = max(vc.intermittent_fans, table_5_fan_default)
+    intermittent_fans = (
+        vc.intermittent_fans if vc.intermittent_fans > 0 else table_5_fan_default
+    )
     wind_kwargs: dict[str, tuple[float, ...]] = (
         {"monthly_wind_speed_m_s": postcode_climate.monthly_wind_speed_m_per_s}
         if postcode_climate is not None else {}
@@ -7272,6 +7306,7 @@ def cert_to_inputs(
         main,
         epc.sap_heating.secondary_heating_type,
         secondary_lodged=_has_lodged_secondary_description(epc),
+        unheated_habitable_rooms=_has_unheated_habitable_rooms(epc),
     )
     # SAP10.2 §4 — compute the worksheet (45..65) values now (they only
     # depend on the cert dwelling shape, not on water_efficiency). The
diff --git a/domain/sap10_calculator/worksheet/heat_transmission.py b/domain/sap10_calculator/worksheet/heat_transmission.py
index 80c65aac..a0d773d9 100644
--- a/domain/sap10_calculator/worksheet/heat_transmission.py
+++ b/domain/sap10_calculator/worksheet/heat_transmission.py
@@ -171,7 +171,12 @@ def _synthesised_window_u_raw(windows: Optional[Sequence[SapWindow]]) -> float:
         if isinstance(code, int)
         else ("double", None)
     )
-    return u_window(installed_year=year, glazing_type=glaze, frame_type=w.frame_material)
+    return u_window(
+        installed_year=year,
+        glazing_type=glaze,
+        frame_type=w.frame_material,
+        glazing_gap=w.glazing_gap,
+    )
 # RdSAP10 §15 "Rounding of data" (p.66): "All element areas (gross)
 # including window areas and conservatory wall area: 2 d.p." plus
 # "U-values: 2 d.p.". This is the data-passed-to-SAP-calculator
diff --git a/domain/sap10_ml/rdsap_uvalues.py b/domain/sap10_ml/rdsap_uvalues.py
index 33b9741c..6687491f 100644
--- a/domain/sap10_ml/rdsap_uvalues.py
+++ b/domain/sap10_ml/rdsap_uvalues.py
@@ -226,6 +226,26 @@ def _u_stone_thin_wall_age_a_to_e(
     return None
 
 
+def _table_3_stone_thickness(band: str, country: Country) -> int:
+    """RdSAP 10 §3.5 Table 3 (PDF p.20) — default stone wall thickness (mm)
+    used "only when the wall thickness could not be measured".
+
+    Stone row:  A-D = 500, E = 450, F-H = 420, I+ = 450.
+    Scotland footnote (*): add 200 mm for bands A and B, 100 mm for other
+    bands. Only A-E reach this helper (the §5.6 formula gate), so the F+
+    branches are defensive.
+    """
+    if band in ("A", "B", "C", "D"):
+        base = 500
+    elif band == "E":
+        base = 450
+    else:
+        base = 420
+    if country == Country.SCT:
+        base += 200 if band in ("A", "B") else 100
+    return base
+
+
 def _u_brick_thin_wall_age_a_to_e(wall_thickness_mm: int) -> float:
     """RdSAP 10 §5.7 Table 13 (PDF p.41) — default U-value for an
     uninsulated solid brick wall by lodged thickness, age bands A-E.
@@ -419,14 +439,16 @@ _CAVITY_FILLED_ENG: Final[list[float]] = [
 # entries that differ from the England base.
 _COUNTRY_KLM_OVERRIDES: Final[dict[Country, dict[tuple[int, int], dict[str, float]]]] = {
     Country.SCT: {
-        # Scotland Cavity-as-built K-M: 0.25, 0.22, 0.17 (vs ENG 0.30, 0.28, 0.26).
-        (WALL_CAVITY, 0): {"H": 0.45, "K": 0.25, "L": 0.22, "M": 0.17},
-        (WALL_STONE_GRANITE, 0): {"H": 0.45, "K": 0.25, "L": 0.22, "M": 0.17},
-        (WALL_STONE_SANDSTONE, 0): {"H": 0.45, "K": 0.25, "L": 0.22, "M": 0.17},
-        (WALL_SOLID_BRICK, 0): {"H": 0.45, "K": 0.25, "L": 0.22, "M": 0.17},
-        (WALL_TIMBER_FRAME, 0): {"K": 0.25, "L": 0.22, "M": 0.17},
-        (WALL_SYSTEM_BUILT, 0): {"H": 0.45, "K": 0.25, "L": 0.22, "M": 0.17},
-        (WALL_COB, 0): {"K": 0.25, "L": 0.22, "M": 0.17},
+        # Scotland (Table 7, PDF p.35) as-built bands that diverge from the
+        # England base: H 0.60→0.45 (not timber/cob, which are already 0.40/
+        # 0.60), J 0.35→0.30 (ALL types), K 0.30→0.25, L 0.28→0.22, M 0.26→0.17.
+        (WALL_CAVITY, 0): {"H": 0.45, "J": 0.30, "K": 0.25, "L": 0.22, "M": 0.17},
+        (WALL_STONE_GRANITE, 0): {"H": 0.45, "J": 0.30, "K": 0.25, "L": 0.22, "M": 0.17},
+        (WALL_STONE_SANDSTONE, 0): {"H": 0.45, "J": 0.30, "K": 0.25, "L": 0.22, "M": 0.17},
+        (WALL_SOLID_BRICK, 0): {"H": 0.45, "J": 0.30, "K": 0.25, "L": 0.22, "M": 0.17},
+        (WALL_TIMBER_FRAME, 0): {"J": 0.30, "K": 0.25, "L": 0.22, "M": 0.17},
+        (WALL_SYSTEM_BUILT, 0): {"H": 0.45, "J": 0.30, "K": 0.25, "L": 0.22, "M": 0.17},
+        (WALL_COB, 0): {"J": 0.30, "K": 0.25, "L": 0.22, "M": 0.17},
     },
     Country.NIR: {
         (WALL_CAVITY, 0): {"M": 0.18},
@@ -567,28 +589,53 @@ def u_wall(
     ctry = country if country is not None else Country.ENG
     age_idx = _age_index(age_band)
     band = _AGE_BANDS[age_idx]
-    # RdSAP 10 §5.6 (PDF p.40) — uninsulated stone wall thin-wall
-    # formula, age bands A-E. Fires only when a documentary wall
-    # thickness is lodged (per §5.3 documentary-evidence rule).
-    # §5.8 + Table 14 dry-line adjustment applies on top.
+    # RdSAP 10 Tables 6-10 stone rows + footnote (a) (PDF p.33-39), §5.6
+    # formula (PDF p.40), §5.8 + Table 14 (PDF p.41-42). A documentary wall
+    # thickness (per §5.3) routes stone in age bands A-E off the §5.6 formula,
+    # NOT the flat Table-6 typical-thickness default:
+    #   - Bands A-D: pure §5.6 formula, UNCAPPED. The stone rows read
+    #     "According to 5.6" with NO 1.7 entry, because a thin/standard solid
+    #     stone wall genuinely loses more than the typical default (sandstone
+    #     400 mm → 1.90, granite 120 mm → 3.89).
+    #   - Band E: the stone row reads "1.7 a"; footnote (a) = "Or from
+    #     equations in 5.6 if the calculated U-value is less than 1.7" →
+    #     U_E = min(formula, 1.7). Scotland sandstone/limestone age E defaults
+    #     to 1.5 (Table 7), granite/whinstone stays 1.7. The 1.7 (1.5) cap
+    #     belongs ONLY at age E, never A-D.
+    # The insulation STATE is NOT a gate: an "as built / insulation Unknown"
+    # lodgement (`wall_insulation_type` None or 4) takes the formula too. Cert
+    # 000565 Ext1 (granite 50 mm, age E, insulation Unknown) → min(6.09, 1.7)
+    # = 1.70, matching the U985 worksheet WITHOUT a flat-table detour — the
+    # age-E cap, not an insulation gate, is what produces the 1.70.
     #
-    # Table 6 footnote (a) (PDF p.34): "Or from equations in 5.6 if
-    # the calculated U-value is less than 1.7." The cap applies only
-    # to the AS-BUILT (no insulation, no dry-line) Table 6 row — for
-    # thin walls where §5.6 gives U ≥ 1.7 (e.g. granite at W=50 mm
-    # yields 6.09 → use Table 6 default 1.7 instead). When the wall
-    # is dry-lined or insulated, the raw §5.6 result feeds the §5.8
-    # chain as the input U₀ — the Table 6 footnote doesn't cap that
-    # path (verified empirically against cert 000565 Main alt_wall_1:
-    # granite W=120 mm dry-lined → U₀=3.88 raw + dry-line → 2.34
-    # matches worksheet, NOT 1.7 + dry-line → 1.32).
+    # When no documentary thickness is lodged, §3.5 Table 3 (PDF p.20) gives
+    # the default thickness to feed the formula (stone A-D = 500 mm, E = 450,
+    # Scotland +200/+100) — NOT a flat 1.7. This matches Elmhurst: an age-B
+    # granite as-built wall with unknown thickness defaults to 500 mm →
+    # 45.315 × 500^(-0.513) = 1.87 (sandstone → 1.68).
     if (
-        wall_thickness_mm is not None
-        and band in _STONE_AGE_A_TO_E
+        band in _STONE_AGE_A_TO_E
         and construction in (WALL_STONE_GRANITE, WALL_STONE_SANDSTONE)
     ):
-        u0 = _u_stone_thin_wall_age_a_to_e(construction, wall_thickness_mm)
+        w = (
+            wall_thickness_mm
+            if wall_thickness_mm is not None
+            else _table_3_stone_thickness(band, ctry)
+        )
+        u0 = _u_stone_thin_wall_age_a_to_e(construction, w)
         if u0 is not None:
+            # Footnote (a) cap is age-E only: clamp the as-built U to the
+            # Table-6/7 age-E default (1.7, or 1.5 for Scotland sandstone/
+            # limestone) when the §5.6 formula exceeds it. A-D stay uncapped.
+            if band == "E":
+                e_default = (
+                    1.5
+                    if ctry == Country.SCT
+                    and construction == WALL_STONE_SANDSTONE
+                    else 1.7
+                )
+                if u0 >= e_default:
+                    u0 = e_default
             # RdSAP 10 §5.8 + Table 14 (PDF p.41-42) — added External/Internal
             # insulation on a stone wall: U = 1/(1/U₀ + R_ins), with U₀ the
             # RAW §5.6 stone result (the Table-6 footnote (a) 1.7 cap does NOT
@@ -628,8 +675,12 @@ def u_wall(
                         Decimal("0.01"), rounding=ROUND_HALF_UP
                     )
                 )
-            if u0 >= 1.7:
-                return 1.7  # Table-6 row cap per footnote (a)
+            # As-built (uninsulated, not dry-lined) stone wall, age A-E:
+            # return the §5.6 result — uncapped for A-D, age-E-capped above.
+            # A thin solid stone wall genuinely has U > 1.7 (sandstone 400 mm
+            # = 1.90, granite 120 mm = 3.89); capping A-D to 1.7 under-counts
+            # fabric loss and over-rates. Confirmed against Elmhurst (age-B
+            # sandstone 400 mm → 1.90) and the §5.6 Table-12 formula tests.
             return u0
     known_types = {
         WALL_STONE_GRANITE, WALL_STONE_SANDSTONE, WALL_SOLID_BRICK, WALL_CAVITY,
@@ -788,20 +839,21 @@ _ROOF_RAFTERS_BY_THICKNESS: Final[list[tuple[int, float]]] = [
     (400, 0.14),
 ]
 
-# Table 18 rafters column: pitched-roof "insulation at rafters" default U
-# by age band when the thickness cannot be determined. RdSAP 10 §5.11
-# Table 18 (PDF p.45). Identical to the joist column (1) for bands A-G
+# Table 18 column (2) "Pitched, insulation at rafters": pitched-roof default
+# U by age band when the thickness cannot be determined. RdSAP 10 §5.11
+# Table 18 (PDF p.46). Identical to the joist column (1) for bands A-G
 # (2.30 → 0.40), then diverges higher (H 0.35 vs 0.30, I 0.35 vs 0.26,
-# J/K 0.20 vs 0.16, L 0.18 vs 0.16). Unlike the loft-joist default this
-# does NOT collapse to the optimistic 0.40 "assume modern retrofit" floor
-# at old bands — a rafter cavity cannot be topped up from the loft, so an
-# unknown-thickness rafter roof keeps the as-built age-band U (band F
-# 0.68, band E 1.50, A-D 2.30). Worksheet-validated by simulated case 41
-# Ext3 (band F, R Rafters, As Built → P960 §3 (30) U=0.68).
+# J/K 0.20 vs 0.16, L 0.18 vs 0.16) before converging to 0.15 at band M.
+# Unlike the loft-joist default this does NOT collapse to the optimistic
+# 0.40 "assume modern retrofit" floor at old bands — a rafter cavity cannot
+# be topped up from the loft, so an unknown-thickness rafter roof keeps the
+# as-built age-band U (band F 0.68, band E 1.50, A-D 2.30). Worksheet-
+# validated by simulated case 41 Ext3 (band F, R Rafters, As Built → P960
+# §3 (30) U=0.68).
 _ROOF_RAFTERS_BY_AGE: Final[dict[str, float]] = {
     "A": 2.30, "B": 2.30, "C": 2.30, "D": 2.30, "E": 1.50,
     "F": 0.68, "G": 0.40, "H": 0.35, "I": 0.35, "J": 0.20,
-    "K": 0.20, "L": 0.18, "M": 0.18,
+    "K": 0.20, "L": 0.18, "M": 0.15,
 }
 
 # Table 18 column (3): flat-roof default U by age band when thickness unknown.
@@ -1349,12 +1401,51 @@ def u_exposed_floor(
 # ---------------------------------------------------------------------------
 
 
+# RdSAP 10 Table 24 (PDF p.50-51) — pre-2002 (Scotland pre-2003 / NI pre-2006)
+# double and triple glazing split by glazing gap between panes: 6 mm, 12 mm,
+# and 16 mm or more, each with a PVC/wooden and a metal-frame U-value. The
+# 2002+ and 2022+ rows are gap-independent ("any" gap). (pvc, metal) per gap:
+_PRE_2002_DOUBLE_U_BY_GAP: Final[dict[str, tuple[float, float]]] = {
+    "6": (3.1, 3.7), "12": (2.8, 3.4), "16+": (2.7, 3.3),
+}
+_PRE_2002_TRIPLE_U_BY_GAP: Final[dict[str, tuple[float, float]]] = {
+    "6": (2.4, 2.9), "12": (2.1, 2.6), "16+": (2.0, 2.5),
+}
+
+
+def _glazing_gap_row(glazing_gap: "str | int | None") -> str:
+    """Map a lodged glazing gap to its Table 24 row key ("6" / "12" / "16+").
+
+    The cert lodges discrete gaps as the int 6 or 12 or the string "16+"
+    (RdSAP-Schema `glazing_gap`). Unknown gap (None) defaults to the 12 mm
+    row — the spec's typical pre-2002 sealed unit. Robust to intermediate
+    integers: <=8 → 6 mm, >=15 → 16 mm-or-more, else 12 mm."""
+    if glazing_gap is None:
+        return "12"
+    if isinstance(glazing_gap, str):
+        s = glazing_gap.strip().lower()
+        if "16" in s or "+" in s:
+            return "16+"
+        try:
+            g = int(float(s))
+        except ValueError:
+            return "12"
+    else:
+        g = int(glazing_gap)
+    if g <= 8:
+        return "6"
+    if g >= 15:
+        return "16+"
+    return "12"
+
+
 def u_window(
     installed_year: Optional[int],
     glazing_type: Optional[str],
     frame_type: Optional[str],
+    glazing_gap: "str | int | None" = None,
 ) -> float:
-    """RdSAP10 window U-value in W/m^2K, never null."""
+    """RdSAP10 window U-value in W/m^2K, never null (RdSAP 10 Table 24)."""
     if glazing_type is None and installed_year is None and frame_type is None:
         return 2.5
     glaze = (glazing_type or "double").lower()
@@ -1367,13 +1458,15 @@ def u_window(
 
     # double/triple glazing — period bands.
     if installed_year is not None and installed_year >= 2022:
-        return 1.4
+        # Table 24 "2022 or later" row: PVC/wood 1.4, metal 1.6.
+        return 1.6 if metal else 1.4
     if installed_year is not None and installed_year >= 2002:
         return 2.2 if metal else 2.0
-    # pre-2002 double/triple default to 12mm gap row.
-    if glaze == "triple":
-        return 2.6 if metal else 2.1
-    return 3.4 if metal else 2.8
+    # pre-2002 double/triple — Table 24 splits by glazing gap (6/12/16+ mm).
+    gap_row = _glazing_gap_row(glazing_gap)
+    table = _PRE_2002_TRIPLE_U_BY_GAP if glaze == "triple" else _PRE_2002_DOUBLE_U_BY_GAP
+    pvc_u, metal_u = table[gap_row]
+    return metal_u if metal else pvc_u
 
 
 # ---------------------------------------------------------------------------
diff --git a/domain/sap10_ml/tests/test_rdsap_uvalues.py b/domain/sap10_ml/tests/test_rdsap_uvalues.py
index 38efc93c..4fb51f42 100644
--- a/domain/sap10_ml/tests/test_rdsap_uvalues.py
+++ b/domain/sap10_ml/tests/test_rdsap_uvalues.py
@@ -421,6 +421,42 @@ def test_u_wall_scotland_age_band_m_returns_country_specific_table7_value() -> N
     assert result == pytest.approx(0.17, abs=0.001)
 
 
+def test_u_wall_scotland_age_band_j_returns_0_30_not_england_0_35_per_table7() -> None:
+    # Arrange — RdSAP 10 Table 7 (Scotland, PDF p.35) as-built band J is
+    # 0.30 for every uninsulated wall type, vs the England base 0.35
+    # (Table 6). The _COUNTRY_KLM_OVERRIDES[SCT] dicts previously listed
+    # H/K/L/M but omitted J, so a Scotland band-J cavity wrongly fell
+    # through to England's 0.35.
+
+    # Act
+    result = u_wall(
+        country=Country.SCT,
+        age_band="J",
+        construction=WALL_CAVITY,
+        insulation_thickness_mm=0,
+    )
+
+    # Assert
+    assert result == pytest.approx(0.30, abs=0.001)
+
+
+def test_u_wall_scotland_age_band_j_timber_frame_returns_0_30_per_table7() -> None:
+    # Arrange — the J=0.30 override applies to all 7 as-built wall types,
+    # including timber frame (England base J = 0.35). Guards the type whose
+    # Scotland override has no H entry (timber H already 0.40 in England).
+
+    # Act
+    result = u_wall(
+        country=Country.SCT,
+        age_band="J",
+        construction=WALL_TIMBER_FRAME,
+        insulation_thickness_mm=0,
+    )
+
+    # Assert
+    assert result == pytest.approx(0.30, abs=0.001)
+
+
 def test_u_wall_timber_frame_as_built_age_band_a_returns_table6_value() -> None:
     # Arrange — Timber frame as built, age A, England -> 2.5 W/m^2K.
 
@@ -826,13 +862,14 @@ def test_u_wall_stone_granite_age_g_with_wall_thickness_ignores_5_6_formula_per_
     assert abs(result - 0.60) <= 1e-3
 
 
-def test_u_wall_stone_granite_age_a_without_wall_thickness_returns_table_6_age_a_default() -> None:
-    # Arrange — §5.6 formula only fires when a wall thickness is
-    # lodged. Without documentary wall-thickness evidence, fall back
-    # to the Table 6 row (which represents typical thickness). For
-    # age A stone granite without thickness, the cascade preserves
-    # its existing "as-built typical" U value rather than the formula
-    # extrapolation.
+def test_u_wall_stone_granite_age_a_without_wall_thickness_uses_table_3_default_500mm() -> None:
+    # Arrange — when no documentary wall thickness is lodged, RdSAP 10 §3.5
+    # Table 3 (PDF p.20) supplies the default stone thickness (A-D = 500 mm),
+    # which feeds the §5.6 formula — NOT a flat 1.7. This matches Elmhurst:
+    # an as-built granite/whinstone wall with unknown thickness defaults to
+    # 500 mm → U = 45.315 × 500^(-0.513) = 1.8693. (The earlier 1.7
+    # expectation was a setup error: Table 6 reads "According to 5.6" for
+    # bands A-D, with no 1.7 entry.)
 
     # Act
     result = u_wall(
@@ -845,8 +882,138 @@ def test_u_wall_stone_granite_age_a_without_wall_thickness_returns_table_6_age_a
         wall_thickness_mm=None,
     )
 
-    # Assert — _TYPICAL_STONE_UNINSULATED at age A = 1.7 (cohort default).
-    assert abs(result - 1.7) <= 1e-3
+    # Assert — §5.6 formula at the Table-3 default 500 mm.
+    assert abs(result - 1.8693) <= 1e-3
+
+
+def test_u_wall_stone_sandstone_age_b_without_wall_thickness_uses_table_3_default_500mm() -> None:
+    # Arrange — sandstone/limestone variant of the Table-3 default: age B,
+    # unknown thickness → 500 mm → 54.876 × 500^(-0.561) = 1.6798. This is
+    # the "500 mm → sandstone 1.68" Elmhurst default.
+
+    # Act
+    result = u_wall(
+        country=Country.ENG,
+        age_band="B",
+        construction=WALL_STONE_SANDSTONE,
+        insulation_thickness_mm=None,
+        insulation_present=False,
+        wall_insulation_type=4,
+        wall_thickness_mm=None,
+    )
+
+    # Assert
+    assert abs(result - 1.6798) <= 1e-3
+
+
+def test_u_wall_stone_sandstone_scotland_age_a_without_thickness_adds_200mm_per_table_3() -> None:
+    # Arrange — Table 3 Scotland footnote (*): add 200 mm for bands A and B.
+    # Age-A Scotland sandstone unknown thickness → 500 + 200 = 700 mm →
+    # 54.876 × 700^(-0.561) = 1.3909 (< 1.7, no age-E cap at band A).
+
+    # Act
+    result = u_wall(
+        country=Country.SCT,
+        age_band="A",
+        construction=WALL_STONE_SANDSTONE,
+        insulation_thickness_mm=None,
+        insulation_present=False,
+        wall_insulation_type=4,
+        wall_thickness_mm=None,
+    )
+
+    # Assert
+    assert abs(result - 1.3909) <= 1e-3
+
+
+def test_u_wall_stone_granite_age_e_50mm_caps_at_table6_default_1_7() -> None:
+    # Arrange — RdSAP 10 Table 6 (England, PDF p.33-34) stone row reads
+    # "1.7 a" at age E, footnote (a) = "Or from equations in 5.6 if the
+    # calculated U-value is less than 1.7". A 50 mm granite wall's §5.6
+    # formula gives U = 45.315 × 50^(-0.513) = 6.09 (> 1.7), so the age-E
+    # default 1.7 stands → min(6.09, 1.7) = 1.70. The cap is age-E ONLY:
+    # bands A-D are uncapped (120 mm age-A granite = 3.89). Insulation is
+    # Unknown (wall_insulation_type None) — no longer a gate. Cert 000565
+    # BP Ext1 is this fixture (U985 worksheet U = 1.70).
+
+    # Act
+    result = u_wall(
+        country=Country.ENG,
+        age_band="E",
+        construction=WALL_STONE_GRANITE,
+        insulation_thickness_mm=None,
+        insulation_present=False,
+        wall_insulation_type=None,
+        dry_lined=False,
+        wall_thickness_mm=50,
+    )
+
+    # Assert
+    assert abs(result - 1.70) <= 1e-3
+
+
+def test_u_wall_stone_sandstone_age_e_thick_wall_uses_5_6_formula_below_1_7() -> None:
+    # Arrange — footnote (a) at age E: use the §5.6 formula when it gives
+    # < 1.7. A 600 mm sandstone wall → U = 54.876 × 600^(-0.561) = 1.5165
+    # (< 1.7), so the formula value is used, NOT the 1.7 default.
+
+    # Act
+    result = u_wall(
+        country=Country.ENG,
+        age_band="E",
+        construction=WALL_STONE_SANDSTONE,
+        insulation_thickness_mm=None,
+        insulation_present=False,
+        wall_insulation_type=None,
+        dry_lined=False,
+        wall_thickness_mm=600,
+    )
+
+    # Assert
+    assert abs(result - 1.5165) <= 1e-3
+
+
+def test_u_wall_stone_sandstone_scotland_age_e_caps_at_1_5_not_1_7() -> None:
+    # Arrange — RdSAP 10 Table 7 (Scotland, PDF p.35) sandstone/limestone
+    # age E default is "1.5 a" (granite/whinstone stays 1.7). A 500 mm
+    # sandstone wall's §5.6 formula = 54.876 × 500^(-0.561) = 1.68 (> 1.5),
+    # so the Scotland age-E default 1.5 stands → min(1.68, 1.5) = 1.50.
+
+    # Act
+    result = u_wall(
+        country=Country.SCT,
+        age_band="E",
+        construction=WALL_STONE_SANDSTONE,
+        insulation_thickness_mm=None,
+        insulation_present=False,
+        wall_insulation_type=None,
+        dry_lined=False,
+        wall_thickness_mm=500,
+    )
+
+    # Assert
+    assert abs(result - 1.50) <= 1e-3
+
+
+def test_u_wall_stone_granite_scotland_age_e_50mm_stays_capped_at_1_7() -> None:
+    # Arrange — Scotland granite/whinstone age E default is 1.7 (only
+    # sandstone/limestone drops to 1.5, Table 7 PDF p.35). A 50 mm granite
+    # wall's formula 6.09 (> 1.7) → min(6.09, 1.7) = 1.70, NOT 1.5.
+
+    # Act
+    result = u_wall(
+        country=Country.SCT,
+        age_band="E",
+        construction=WALL_STONE_GRANITE,
+        insulation_thickness_mm=None,
+        insulation_present=False,
+        wall_insulation_type=None,
+        dry_lined=False,
+        wall_thickness_mm=50,
+    )
+
+    # Assert
+    assert abs(result - 1.70) <= 1e-3
 
 
 def test_u_wall_curtain_wall_missing_age_lodgement_defaults_to_pre_2023_u_2p0_per_rdsap_5_18() -> None:
@@ -1098,6 +1265,25 @@ def test_u_roof_at_rafters_unknown_thickness_uses_table18_rafters_age_band() ->
     assert abs(band_c - 2.30) <= 0.001
 
 
+def test_u_roof_at_rafters_unknown_thickness_age_m_returns_0_15_per_table18() -> None:
+    # Arrange — RdSAP 10 Table 18 column (2) "Pitched, insulation at
+    # rafters" (PDF p.46): band M = 0.15 (footnote (1) only, no country
+    # variation — the whole M row converges to 0.15). The rafters column
+    # diverges above the joist column at H-L (0.35/0.35/0.20/0.20/0.18)
+    # but rejoins it at M = 0.15; the table previously carried 0.18 here.
+
+    # Act
+    band_m = u_roof(
+        country=Country.ENG,
+        age_band="M",
+        insulation_thickness_mm=None,
+        insulation_at_rafters=True,
+    )
+
+    # Assert
+    assert abs(band_m - 0.15) <= 0.001
+
+
 def test_u_roof_unknown_age_band_falls_back_to_mid_range() -> None:
     # Arrange — nothing known.
 
@@ -1562,6 +1748,42 @@ def test_u_window_post_2022_pvc_returns_low_table24_value() -> None:
     assert result == pytest.approx(1.4, abs=0.001)
 
 
+def test_u_window_post_2022_metal_returns_table24_1_6_not_pvc_1_4() -> None:
+    # Arrange — Table 24 "2022 or later" row (PDF p.51): PVC/wooden frame
+    # 1.4, METAL frame 1.6. The metal frame variant was previously ignored
+    # (1.4 returned for both), under-counting metal-frame heat loss.
+
+    # Act
+    result = u_window(installed_year=2023, glazing_type="double", frame_type="metal")
+
+    # Assert
+    assert result == pytest.approx(1.6, abs=0.001)
+
+
+def test_u_window_pre_2002_double_glazing_gap_selects_table24_row() -> None:
+    # Arrange — RdSAP 10 Table 24 (PDF p.50) pre-2002 double glazing splits
+    # by glazing gap (PVC/wooden frame): 6 mm → 3.1, 12 mm → 2.8, 16 mm or
+    # more → 2.7. The cert lodges the gap as the int 6/12 or the string
+    # "16+"; unknown gap defaults to the 12 mm row.
+
+    # Act / Assert
+    assert u_window(installed_year=None, glazing_type="double", frame_type="pvc", glazing_gap=6) == pytest.approx(3.1, abs=0.001)
+    assert u_window(installed_year=None, glazing_type="double", frame_type="pvc", glazing_gap=12) == pytest.approx(2.8, abs=0.001)
+    assert u_window(installed_year=None, glazing_type="double", frame_type="pvc", glazing_gap="16+") == pytest.approx(2.7, abs=0.001)
+    assert u_window(installed_year=None, glazing_type="double", frame_type="pvc", glazing_gap=None) == pytest.approx(2.8, abs=0.001)
+
+
+def test_u_window_pre_2002_triple_glazing_gap_and_metal_frame_select_table24_row() -> None:
+    # Arrange — Table 24 pre-2002 triple glazing: 6 mm → 2.4, 12 mm → 2.1,
+    # 16 mm+ → 2.0 (PVC); metal frame adds +0.5 per the metal column
+    # (6 → 2.9, 12 → 2.6, 16+ → 2.5).
+
+    # Act / Assert
+    assert u_window(installed_year=None, glazing_type="triple", frame_type="pvc", glazing_gap="16+") == pytest.approx(2.0, abs=0.001)
+    assert u_window(installed_year=None, glazing_type="triple", frame_type="metal", glazing_gap=6) == pytest.approx(2.9, abs=0.001)
+    assert u_window(installed_year=None, glazing_type="triple", frame_type="metal", glazing_gap="16+") == pytest.approx(2.5, abs=0.001)
+
+
 def test_u_window_falls_back_to_mid_range_when_unknown() -> None:
     # Arrange — nothing known.
 
diff --git a/tests/datatypes/epc/domain/test_mapper_glazing_label.py b/tests/datatypes/epc/domain/test_mapper_glazing_label.py
new file mode 100644
index 00000000..8430d76e
--- /dev/null
+++ b/tests/datatypes/epc/domain/test_mapper_glazing_label.py
@@ -0,0 +1,26 @@
+"""Mapper boundary: the Elmhurst §11 "Double between 2002" glazing label.
+
+The full RdSAP-Schema-21 label is "Double between 2002 and 2021" (SAP 10.2
+Table 24 code 3 — double glazing installed 2002-2021). When the Elmhurst
+Summary PDF wraps the trailing "and 2021" into an adjacent table cell the
+extractor joins away, the surfaced label truncates to "Double between 2002"
+(the same artifact already handled for "Triple post or during"). Before this
+was mapped the truncated form raised `UnmappedElmhurstLabel`, blocking the
+whole Summary (surfaced on the simulated-case-46 multi-attribute worksheet).
+"""
+
+from datatypes.epc.domain.mapper import (
+    _elmhurst_glazing_type_code,  # pyright: ignore[reportPrivateUsage]
+)
+
+
+def test_truncated_double_between_2002_maps_to_code_3() -> None:
+    # Arrange — the year-truncated form of "Double between 2002 and 2021".
+
+    # Act
+    code = _elmhurst_glazing_type_code("Double between 2002")
+    full = _elmhurst_glazing_type_code("Double between 2002 and 2021")
+
+    # Assert — both resolve to SAP 10.2 Table 24 code 3 (DG 2002-2021).
+    assert code == 3
+    assert full == 3
diff --git a/tests/domain/sap10_calculator/rdsap/test_cert_to_inputs.py b/tests/domain/sap10_calculator/rdsap/test_cert_to_inputs.py
index d8934c16..e1ca3f7e 100644
--- a/tests/domain/sap10_calculator/rdsap/test_cert_to_inputs.py
+++ b/tests/domain/sap10_calculator/rdsap/test_cert_to_inputs.py
@@ -1104,6 +1104,59 @@ def test_secondary_fraction_fires_when_secondary_lodged_via_description_only() -
     assert abs(description_lodged - 0.10) <= 1e-9
 
 
+def test_secondary_fraction_fires_for_unheated_habitable_rooms_per_appendix_a22() -> None:
+    # Arrange — SAP 10.2 Appendix A.2.2: when the main system does not heat
+    # every habitable room (heated rooms < habitable rooms), the unheated
+    # rooms take an assumed portable-electric secondary heater, so the Table
+    # 11 0.10 fraction is costed EVEN WITH no lodged secondary. A gas boiler
+    # main (cat 2, not forced-secondary) with no secondary lodged returns 0.0
+    # normally, but 0.10 once `unheated_habitable_rooms=True`. Worksheet-
+    # validated on simulated case 46 (heated 4 < habitable 7): the assumed
+    # secondary lifted our SAP from 39 to 29 (Elmhurst 30).
+    from domain.sap10_calculator.rdsap.cert_to_inputs import _secondary_fraction  # pyright: ignore[reportPrivateUsage]
+
+    main = _gas_boiler_detail()  # cat 2, code 102 — not forced-secondary
+
+    # Act
+    all_rooms_heated = _secondary_fraction(main, None, unheated_habitable_rooms=False)
+    has_unheated = _secondary_fraction(main, None, unheated_habitable_rooms=True)
+
+    # Assert
+    assert all_rooms_heated == 0.0
+    assert abs(has_unheated - 0.10) <= 1e-9
+
+
+def test_has_unheated_habitable_rooms_prefers_flag_and_guards_zero_sentinel() -> None:
+    # Arrange — `_has_unheated_habitable_rooms` prefers the lodged
+    # `any_unheated_rooms` flag; its room-count fallback must NOT trigger on a
+    # `heated_rooms_count == 0` "not provided" sentinel (gov-API), only on a
+    # real positive heated count below the habitable count.
+    import dataclasses
+
+    from domain.sap10_calculator.rdsap.cert_to_inputs import (  # pyright: ignore[reportPrivateUsage]
+        _has_unheated_habitable_rooms,
+    )
+
+    base = make_minimal_sap10_epc(
+        total_floor_area_m2=_TYPICAL_TFA_M2, country_code="ENG",
+    )
+
+    flag_true = dataclasses.replace(base, any_unheated_rooms=True)
+    flag_false = dataclasses.replace(base, any_unheated_rooms=False)
+    count_unheated = dataclasses.replace(
+        base, any_unheated_rooms=None, heated_rooms_count=4, habitable_rooms_count=7
+    )
+    zero_sentinel = dataclasses.replace(
+        base, any_unheated_rooms=None, heated_rooms_count=0, habitable_rooms_count=5
+    )
+
+    # Act / Assert
+    assert _has_unheated_habitable_rooms(flag_true) is True
+    assert _has_unheated_habitable_rooms(flag_false) is False
+    assert _has_unheated_habitable_rooms(count_unheated) is True
+    assert _has_unheated_habitable_rooms(zero_sentinel) is False
+
+
 def test_main_heating_fraction_missing_falls_back_to_table11_default() -> None:
     # Arrange — when main_heating_fraction isn't lodged AND the cert
     # has a secondary system lodged, Table 11's 0.10 default still
@@ -1556,6 +1609,40 @@ def test_ventilation_from_cert_applies_table_5_default_when_lodged_zero() -> Non
     )
 
 
+def test_ventilation_from_cert_uses_lodged_fans_below_age_default_not_floored() -> None:
+    # Arrange — RdSAP 10 §4.1 Table 5 (PDF p.28): "Number of extract fans if
+    # known; if unknown: [age-band default]." The default is an UNKNOWN-
+    # fallback, NOT a floor — a genuinely-lodged positive count is used
+    # as-is even when below the age default. An age-H 6-habitable-room
+    # dwelling has a 3-fan default, but a cert lodging 2 fans must use 2,
+    # not be floored up to 3. (Was `max(lodged, default)` → 3, over-counting
+    # ventilation; surfaced on simulated case 46 where it inflated (8) by
+    # one fan = 0.055 ACH and pushed SAP 30 → 29.)
+    age_h_part = make_building_part(
+        floor_dimensions=[
+            make_floor_dimension(total_floor_area_m2=45.0, floor=0),
+            make_floor_dimension(total_floor_area_m2=45.0, floor=1),
+        ],
+        construction_age_band='H',
+    )
+    epc = make_minimal_sap10_epc(
+        total_floor_area_m2=_TYPICAL_TFA_M2,
+        habitable_rooms_count=6,  # age H-M, 6-8 rooms → Table 5 default 3
+        region_code="1",
+        sap_building_parts=[age_h_part],
+        sap_ventilation=SapVentilation(extract_fans_count=2),  # lodged 2 < 3
+    )
+
+    # Act
+    v = ventilation_from_cert(epc)
+
+    # Assert — (8) openings ACH uses the lodged 2 fans (20 m³/h), not 3.
+    from domain.sap10_calculator.rdsap.cert_to_inputs import dimensions_from_cert
+    vol = dimensions_from_cert(epc).volume_m3
+    assert abs(v.openings_ach - 20.0 / vol) <= 1e-6
+    assert abs(v.openings_ach - 30.0 / vol) > 1e-6
+
+
 def test_ventilation_from_cert_passes_lodged_ap4_to_pressure_test_ach_per_sap_10_2_section_2_line_18() -> None:
     # Arrange — SAP 10.2 §2 line (17a)/(18) "Air permeability value, AP4
     # (m³/h/m²)": when a Pulse pressure test is lodged the cascade must
diff --git a/tests/domain/sap10_calculator/test_calculator.py b/tests/domain/sap10_calculator/test_calculator.py
index dba25409..5444a140 100644
--- a/tests/domain/sap10_calculator/test_calculator.py
+++ b/tests/domain/sap10_calculator/test_calculator.py
@@ -270,6 +270,28 @@ def test_calculator_returns_twelve_month_breakdown_and_plausible_sap_score() ->
     )
 
 
+def test_sap_score_continuous_floored_at_1_for_degenerate_high_cost() -> None:
+    # Arrange — SAP 10.2 §13 / RdSAP 10 §13: the SAP rating is floored at 1
+    # ("if the result of the calculation is less than 1, the rating is 1").
+    # Drive the cost so high that the raw ECF formula returns a negative SAP
+    # (a degenerate dwelling, e.g. a cert lodged at the floor of 1); both the
+    # integer AND the continuous score must clamp to 1 rather than emit a
+    # physically impossible negative rating.
+    inputs = replace(
+        _baseline_inputs(),
+        space_heating_fuel_cost_gbp_per_kwh=5.0,
+        hot_water_fuel_cost_gbp_per_kwh=5.0,
+        other_fuel_cost_gbp_per_kwh=5.0,
+    )
+
+    # Act
+    result = calculate_sap_from_inputs(inputs)
+
+    # Assert — raw SAP would be < 1 here; the floor holds on both outputs.
+    assert result.sap_score == 1
+    assert abs(result.sap_score_continuous - 1.0) <= 1e-9
+
+
 def test_calculate_exposes_dimensions_intermediates() -> None:
     # Arrange — P5 trace mode: `result.intermediate` must surface the
     # worksheet-named dimensions variables for per-section diffing
diff --git a/tests/infrastructure/epc_client/test_sap_accuracy_corpus.py b/tests/infrastructure/epc_client/test_sap_accuracy_corpus.py
index ef933adb..df64ed59 100644
--- a/tests/infrastructure/epc_client/test_sap_accuracy_corpus.py
+++ b/tests/infrastructure/epc_client/test_sap_accuracy_corpus.py
@@ -150,10 +150,53 @@ _CORPUS = Path(
 # MAE 0.12 -> 0.08 t/yr (bias +0.04 -> 0.00). A prior session deferred enum 9
 # ("direction not understood") while the PE/CO2 lens was confounded by the
 # climate-cascade bug (fc7c4d2d); the corrected lens shows the over-rate.
-_MIN_WITHIN_HALF_SAP = 0.70
-_MAX_SAP_MAE = 0.85
+# UNINSULATED STONE WALL §5.6 FORMULA (RdSAP 10 §5.6 Table 12, PDF p.40): a
+# stone wall of KNOWN thickness whose insulation STATE is known (As Built /
+# external / internal) is billed by the §5.6 formula on its lodged thickness
+# (sandstone/limestone U = 54.876·W^-0.561, granite/whinstone 45.315·W^-0.513),
+# NOT capped at the Table-6 typical-thickness 1.7. The old `if u0>=1.7: 1.7`
+# cap nullified the formula for every real-thickness stone wall (it only dips
+# below 1.7 past ~488 mm sandstone / ~640 mm granite) and under-counted fabric
+# loss → over-rate. Gated on `wall_insulation_type is not None` so an
+# "insulation Unknown" wall still falls to the Table-6 default (cert 000565
+# Ext1: granite 50 mm + Unknown → worksheet 1.70, not the formula's 6.09).
+# Took within-0.5 70.3% -> 71.6% (MAE 0.833 -> 0.822); fixed the 2 stone-U
+# unit tests; worksheet-validated (Elmhurst age-B sandstone 400 mm → 1.90).
+#
+# STONE MECHANISM CORRECTED (RdSAP 10 Tables 6-7 footnote a + §3.5 Table 3):
+# the commit above (034d4b7c) got the right numbers for two cases but the
+# wrong mechanism — it dropped the 1.7 cap for ALL age bands and gated on
+# `wall_insulation_type is not None`. Per Tables 6-10: bands A-D = uncapped
+# §5.6 formula, band E = min(formula, 1.7) (Scotland sandstone 1.5); the cap
+# is age-E ONLY. The insulation-state gate is not a spec rule (it sent
+# age-A-D "insulation Unknown" stone to the flat 1.7 table). Unknown
+# thickness now feeds the §3.5 Table-3 default thickness (stone A-D 500 mm,
+# E 450; Scotland +200/+100) into the formula — Elmhurst defaults an England
+# age-B granite as-built unknown-thickness wall to 500 mm → 1.87 (sandstone
+# 1.68), NOT a flat 1.7. Also added the missing Scotland band-J 0.30 override
+# (Table 7) for all 7 as-built wall types. MAE 0.822 -> 0.819, PE 3.7 -> 3.6;
+# within-0.5 and CO2 unchanged. Unit-pinned in test_rdsap_uvalues.
+#
+# SAP RATING FLOOR (SAP 10.2 §13 / RdSAP 10 §13): the rating is floored at 1
+# ("if the result is less than 1, the rating is 1"). `calculate_sap_from_inputs`
+# now applies that floor to the CONTINUOUS score too (was integer-only), so a
+# degenerate dwelling no longer emits a negative SAP. Removed a -12.3 outlier
+# (cert 422000111926, lodged at the floor of 1, was computing -11.3): within-0.5
+# 70.2% -> 70.3%, MAE 0.845 -> 0.833.
+# EXTRACT-FAN DEFAULT IS UNKNOWN-FALLBACK, NOT A FLOOR (RdSAP 10 §4.1 Table 5,
+# PDF p.28). Table 5 reads "Number of extract fans if known; if unknown:
+# [age-band default]". The cascade applied `max(lodged, age_default)`, flooring
+# a genuinely-lodged count up to the age-band minimum (e.g. an age H-M dwelling
+# lodging 2 fans billed at the 3-fan default), over-counting ventilation line
+# (8) and the HLC. Fixed to `lodged if lodged > 0 else default` (a lodged 0 is
+# the Elmhurst/RdSAP "unknown" form → default; any positive count is literal).
+# within-0.5 71.6% -> 72.5%, MAE 0.819 -> 0.815. Surfaced by Khalim's Elmhurst
+# stress worksheet (simulated case 46): closed its last ventilation residual
+# (our Jan ACH 9.14 -> 9.0748 exact; SAP 29 -> 30 = accredited Elmhurst).
+_MIN_WITHIN_HALF_SAP = 0.72
+_MAX_SAP_MAE = 0.82
 _MAX_CO2_MAE_TONNES = 0.09      # t CO2 / yr vs co2_emissions_current
-_MAX_PE_PER_M2_MAE = 4.0        # kWh / m2 / yr vs energy_consumption_current
+_MAX_PE_PER_M2_MAE = 3.7        # kWh / m2 / yr vs energy_consumption_current
 
 
 def _load_corpus() -> list[dict[str, Any]]: