Recommend loft insulation for a loft below the building-regs depth 🟩

A lodged numeric loft depth below the 270mm building-regs compliance gate is
now eligible (topped up to the 300mm install depth), regardless of whether the
roof type is lodged, since a measured depth is a positive statement of a real
loft. Sentinels keep their ADR-0047 resolution. Fixes property 724702 (50mm
loft) which previously returned no recommendation. ADR-0063.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

domain/modelling/generators/roof_recommendation.py

@@ -30,6 +30,12 @@ _SLOPING_CEILING_MEASURE_TYPE = MeasureType.SLOPING_CEILING_INSULATION
 # measure at 300 mm; pinning the before→after cascade (000490/001431) requires
 # the overlay to match that depth exactly (see test_elmhurst_cascade_pins).
 _RECOMMENDED_LOFT_THICKNESS_MM = 300
+# Building Regulations Approved Document L loft/ceiling compliance gate (mm): a
+# lodged loft shallower than this is sub-standard and eligible for a top-up to
+# `_RECOMMENDED_LOFT_THICKNESS_MM` (ADR-0063). The gate (270, "is this at
+# building regs?") and the install depth (300, "how deep do we lay it?") are
+# deliberately different numbers.
+_BUILDING_REGS_LOFT_DEPTH_MM: Final[int] = 270
 # Recommended sloping-ceiling depth (mm); Elmhurst re-lodges 100 mm (ADR-0021).
 _RECOMMENDED_SLOPING_CEILING_THICKNESS_MM = 100
 # Age bands whose as-built pitched roof is uninsulated (ADR-0047: A-D
@@ -62,6 +68,23 @@ def _pitched_roof_is_uninsulated(
             and age_band.upper() in _AS_BUILT_UNINSULATED_AGE_BANDS
         )
     return False
+
+
+def _lodged_numeric_depth_mm(thickness: Union[str, int, None]) -> Optional[int]:
+    """The lodged loft depth as a whole number of millimetres, or None when the
+    value is a sentinel or unlodged (``ND`` / ``NI`` / ``"As Built"`` / None).
+    Parses a bare int, an ``"Nmm"`` string (``"50mm"``), and an ``"Nmm+"`` string
+    (``"400mm+"`` → 400). Non-numeric values return None so they fall through to
+    the sentinel resolution (`_pitched_roof_is_uninsulated`), preserving the
+    ADR-0047 split (ADR-0063)."""
+    if isinstance(thickness, int):
+        return thickness
+    if thickness is None:
+        return None
+    digits: str = thickness.strip().lower().removesuffix("+").removesuffix("mm").strip()
+    return int(digits) if digits.isdigit() else None
+
+
 _FLAT_ROOF_MEASURE_TYPE = MeasureType.FLAT_ROOF_INSULATION
 # Recommended flat-roof depth (mm); Elmhurst re-lodges 200 mm (ADR-0021).
 _RECOMMENDED_FLAT_ROOF_THICKNESS_MM = 200
@@ -134,15 +157,25 @@ def recommend_roof_insulation(
     # codes 6/7 ("(another dwelling above)" / insulated thatch) map the type
     # to None and real code-7 certs lodge "ND" — with zero roof heat loss
     # (RdSAP 10 Table 18), so only an explicit 0 may trigger it.
+    # A lodged NUMERIC depth is a positive statement of a real, accessible loft
+    # (a party ceiling never lodges a measured roof depth), so it is eligible
+    # whenever it is below the building-regs compliance gate — regardless of
+    # whether the roof type is lodged, and covering the explicit-0 uninsulated
+    # case. A SENTINEL (or nothing) keeps the ADR-0047 resolution: known-pitched
+    # resolves by age band, an unlodged type defers (party-ceiling guard).
     known_pitched: bool = "pitched" in roof_type or "thatch" in roof_type
-    uninsulated: bool = (
-        _pitched_roof_is_uninsulated(
+    lodged_depth_mm: Optional[int] = _lodged_numeric_depth_mm(
+        main.roof_insulation_thickness
+    )
+    if lodged_depth_mm is not None:
+        eligible: bool = lodged_depth_mm < _BUILDING_REGS_LOFT_DEPTH_MM
+    elif known_pitched:
+        eligible = _pitched_roof_is_uninsulated(
             main.roof_insulation_thickness, main.construction_age_band
         )
-        if known_pitched
-        else main.roof_insulation_thickness == 0
-    )
-    if not uninsulated:
+    else:
+        eligible = False
+    if not eligible:
         return None
     return _roof_recommendation(
         epc,