diff --git a/tests/domain/epc/test_roof_sloping_ceiling_guard.py b/tests/domain/epc/test_roof_sloping_ceiling_guard.py
index 022b36460..d2820826f 100644
--- a/tests/domain/epc/test_roof_sloping_ceiling_guard.py
+++ b/tests/domain/epc/test_roof_sloping_ceiling_guard.py
@@ -40,3 +40,46 @@ def test_sloping_ceiling_without_a_depth_resolves_to_as_built(
 
     # Assert
     assert member is RoofType.PITCHED_SLOPING_CEILING_AS_BUILT
+
+
+@pytest.mark.parametrize(
+    ("description", "expected"),
+    [
+        # Exact tabulated depths → their own member.
+        ("PitchedWithSlopingCeiling: 12mm", RoofType.PITCHED_SLOPING_CEILING_12MM),
+        ("PitchedWithSlopingCeiling: 100mm", RoofType.PITCHED_SLOPING_CEILING_100MM),
+        ("PitchedWithSlopingCeiling: 150 mm", RoofType.PITCHED_SLOPING_CEILING_150MM),
+        ("PitchedWithSlopingCeiling: 270mm", RoofType.PITCHED_SLOPING_CEILING_270MM),
+        ("PitchedWithSlopingCeiling: 400mm", RoofType.PITCHED_SLOPING_CEILING_400MM),
+        # Off-ladder depth snaps to the nearest tabulated depth ≤ N (mirrors the
+        # calculator's `_ROOF_BY_THICKNESS` picker), so nothing leaks to the LLM.
+        ("PitchedWithSlopingCeiling: 130mm", RoofType.PITCHED_SLOPING_CEILING_125MM),
+        # Above 400 mm, or an explicit "400+" lodgement → the 400+ member.
+        ("PitchedWithSlopingCeiling: 450mm", RoofType.PITCHED_SLOPING_CEILING_400_PLUS),
+        ("PitchedWithSlopingCeiling: 400+mm", RoofType.PITCHED_SLOPING_CEILING_400_PLUS),
+    ],
+)
+def test_sloping_ceiling_measured_depth_resolves_to_its_ladder_member(
+    description: str, expected: RoofType
+) -> None:
+    # ADR-0066: a measured sloping-ceiling depth rides onto the matching ladder
+    # member (Table 17 col (1a)); off-ladder depths snap down; ≥ 400 / "400+"
+    # caps at the top member.
+
+    # Act
+    member = roof_sloping_ceiling_guard(description)
+
+    # Assert
+    assert member is expected
+
+
+def test_sloping_ceiling_depth_below_the_ladder_falls_back_to_as_built() -> None:
+    # No member exists below 12 mm; a sub-ladder depth defers to `as built` (the
+    # age band drives it — uninsulated at old bands anyway), never inventing a
+    # member or leaking to the loft LLM route.
+
+    # Act
+    member = roof_sloping_ceiling_guard("PitchedWithSlopingCeiling: 5mm")
+
+    # Assert
+    assert member is RoofType.PITCHED_SLOPING_CEILING_AS_BUILT