diff --git a/src/AcDream.Core/Physics/TransitionTypes.cs b/src/AcDream.Core/Physics/TransitionTypes.cs
index cc6944a..6494789 100644
--- a/src/AcDream.Core/Physics/TransitionTypes.cs
+++ b/src/AcDream.Core/Physics/TransitionTypes.cs
@@ -623,7 +623,15 @@ public sealed class Transition
             if (!ci.ContactPlaneValid && oi.Contact && !sp.StepDown
                 && sp.CheckCellId != 0 && oi.StepDown)
             {
-                float zVal            = PhysicsGlobals.LandingZ;
+                // L.2.3i (2026-04-29): retail uses FloorZ when OnWalkable,
+                // LandingZ when not. acdream was unconditionally LandingZ —
+                // which let the step-down probe accept steep polygons
+                // (~85° permissive instead of ~49° strict) as the player's
+                // new contact, contributing to the "walks up steep roofs"
+                // bug. Per CTransition::transitional_insert step-down OK
+                // branch (acclient_2013_pseudo_c.txt:273258-273265) and
+                // ACE Transition.cs:849-856.
+                float zVal            = oi.GetWalkableZ();
                 float stepDownHeight  = oi.StepDownHeight;
                 sp.WalkableAllowance  = zVal;
                 sp.SaveCheckPos();
@@ -1638,7 +1646,14 @@ public sealed class Transition
             ci.LastKnownContactPlaneIsWater = ci.ContactPlaneIsWater;
 
             oi.State |= ObjectInfoState.Contact;
-            if (ci.ContactPlane.Normal.Z >= PhysicsGlobals.LandingZ)
+            // L.2.3i (2026-04-29): use FloorZ (~49°) NOT LandingZ (~85°)
+            // for the OnWalkable test. The previous LandingZ check was
+            // far too permissive — a 60° roof (normal.Z=0.5) was being
+            // marked OnWalkable, letting the player walk up steep slopes
+            // they shouldn't reach. Retail's PhysicsObj::is_valid_walkable
+            // uses FloorZ unconditionally (acclient_2013_pseudo_c.txt:277180-277193,
+            // ACE PhysicsObj.cs:2861).
+            if (ci.ContactPlane.Normal.Z >= PhysicsGlobals.FloorZ)
                 oi.State |= ObjectInfoState.OnWalkable;
             else
                 oi.State &= ~ObjectInfoState.OnWalkable;
@@ -1651,7 +1666,8 @@ public sealed class Transition
             // last-known plane. Without this, every wall bump dropped the
             // player into the falling animation for one frame.
             oi.State |= ObjectInfoState.Contact;
-            if (ci.LastKnownContactPlane.Normal.Z >= PhysicsGlobals.LandingZ)
+            // L.2.3i: same FloorZ correction as the live-contact branch.
+            if (ci.LastKnownContactPlane.Normal.Z >= PhysicsGlobals.FloorZ)
                 oi.State |= ObjectInfoState.OnWalkable;
             else
                 oi.State &= ~ObjectInfoState.OnWalkable;