diff --git a/packages/core/src/hooks/spatial-grid/spatial-grid-manager.ts b/packages/core/src/hooks/spatial-grid/spatial-grid-manager.ts
index bc01f718..e266179b 100644
--- a/packages/core/src/hooks/spatial-grid/spatial-grid-manager.ts
+++ b/packages/core/src/hooks/spatial-grid/spatial-grid-manager.ts
@@ -210,6 +210,7 @@ export class SpatialGridManager {
   // Called when nodes change
   handleNodeCreated(node: AnyNode, levelId: string) {
     if (node.type === 'slab') {
+      console.log(`[SpatialGrid] Adding slab ${node.id} to level ${levelId}`, (node as SlabNode).polygon)
       this.getSlabMap(levelId).set(node.id, node as SlabNode)
     } else if (node.type === 'ceiling') {
       this.ceilings.set(node.id, node as CeilingNode)
@@ -448,7 +449,8 @@ export class SpatialGridManager {
   }
 
   /**
-   * Get the slab elevation for a wall by sampling its start, mid, and end points.
+   * Get the slab elevation for a wall by checking if it overlaps with any slab polygon.
+   * Uses wallOverlapsPolygon which handles edge cases (points on boundary, collinear segments).
    * Returns the highest slab elevation found, or 0 if none.
    */
   getSlabElevationForWall(
@@ -457,24 +459,16 @@ export class SpatialGridManager {
     end: [number, number],
   ): number {
     const slabMap = this.slabsByLevel.get(levelId)
+    console.log(`[SpatialGrid] getSlabElevationForWall | levelId: ${levelId} | slabMap size: ${slabMap?.size ?? 0} | slabs:`, slabMap ? Array.from(slabMap.keys()) : [])
     if (!slabMap) return 0
 
-    const samples: [number, number][] = [
-      start,
-      [(start[0] + end[0]) / 2, (start[1] + end[1]) / 2],
-      end,
-    ]
-
     let maxElevation = 0
     for (const slab of slabMap.values()) {
       if (slab.polygon.length < 3) continue
-      for (const [sx, sz] of samples) {
-        if (pointInPolygon(sx, sz, slab.polygon)) {
-          const elevation = slab.elevation ?? 0.05
-          if (elevation > maxElevation) {
-            maxElevation = elevation
-          }
-          break // This slab matched, no need to check more sample points
+      if (wallOverlapsPolygon(start, end, slab.polygon)) {
+        const elevation = slab.elevation ?? 0.05
+        if (elevation > maxElevation) {
+          maxElevation = elevation
         }
       }
     }
diff --git a/packages/core/src/systems/ceiling/ceiling-system.tsx b/packages/core/src/systems/ceiling/ceiling-system.tsx
index 8de4a45d..19b5dd51 100644
--- a/packages/core/src/systems/ceiling/ceiling-system.tsx
+++ b/packages/core/src/systems/ceiling/ceiling-system.tsx
@@ -22,8 +22,9 @@ export const CeilingSystem = () => {
       const mesh = sceneRegistry.nodes.get(id) as THREE.Mesh
       if (mesh) {
         updateCeilingGeometry(node as CeilingNode, mesh)
+        clearDirty(id as AnyNodeId)
       }
-      clearDirty(id as AnyNodeId)
+      // If mesh not found, keep it dirty for next frame
     })
   })
 
diff --git a/packages/core/src/systems/roof/roof-system.tsx b/packages/core/src/systems/roof/roof-system.tsx
index edac2763..ed0611f8 100644
--- a/packages/core/src/systems/roof/roof-system.tsx
+++ b/packages/core/src/systems/roof/roof-system.tsx
@@ -22,8 +22,9 @@ export const RoofSystem = () => {
       const mesh = sceneRegistry.nodes.get(id) as THREE.Mesh
       if (mesh) {
         updateRoofGeometry(node as RoofNode, mesh)
+        clearDirty(id as AnyNodeId)
       }
-      clearDirty(id as AnyNodeId)
+      // If mesh not found, keep it dirty for next frame
     })
   })
 
diff --git a/packages/core/src/systems/slab/slab-system.tsx b/packages/core/src/systems/slab/slab-system.tsx
index e62dda56..99be6a90 100644
--- a/packages/core/src/systems/slab/slab-system.tsx
+++ b/packages/core/src/systems/slab/slab-system.tsx
@@ -22,8 +22,9 @@ export const SlabSystem = () => {
       const mesh = sceneRegistry.nodes.get(id) as THREE.Mesh
       if (mesh) {
         updateSlabGeometry(node as SlabNode, mesh)
+        clearDirty(id as AnyNodeId)
       }
-      clearDirty(id as AnyNodeId)
+      // If mesh not found, keep it dirty for next frame
     })
   })
 
diff --git a/packages/core/src/systems/wall/wall-system.tsx b/packages/core/src/systems/wall/wall-system.tsx
index b5f753d4..c9d9b8e9 100644
--- a/packages/core/src/systems/wall/wall-system.tsx
+++ b/packages/core/src/systems/wall/wall-system.tsx
@@ -53,8 +53,9 @@ export const WallSystem = () => {
         const mesh = sceneRegistry.nodes.get(wallId) as THREE.Mesh
         if (mesh) {
           updateWallGeometry(wallId, miterData)
+          clearDirty(wallId as AnyNodeId)
         }
-        clearDirty(wallId as AnyNodeId)
+        // If mesh not found, keep it dirty for next frame
       }
 
       // Update adjacent walls that share junctions
@@ -106,6 +107,7 @@ function updateWallGeometry(wallId: string, miterData: WallMiterData) {
 
   const levelId = resolveLevelId(node, nodes)
   const slabElevation = spatialGridManager.getSlabElevationForWall(levelId, node.start, node.end)
+  console.log(`[WallSystem] Wall ${node.name || node.id} | levelId: ${levelId} | start: [${node.start}] | end: [${node.end}] | slabElevation: ${slabElevation}`)
 
   const childrenIds = node.children || []
   const childrenNodes = childrenIds
diff --git a/packages/viewer/src/components/renderers/roof/roof-renderer.tsx b/packages/viewer/src/components/renderers/roof/roof-renderer.tsx
index 8c985b1f..31156860 100644
--- a/packages/viewer/src/components/renderers/roof/roof-renderer.tsx
+++ b/packages/viewer/src/components/renderers/roof/roof-renderer.tsx
@@ -21,7 +21,7 @@ export const RoofRenderer = ({ node }: { node: RoofNode }) => {
     >
       {/* RoofSystem will replace this geometry in the next frame */}
       <boxGeometry args={[0, 0, 0]} />
-      <meshStandardMaterial color="#8b4513" />
+      <meshStandardMaterial color="white" />
     </mesh>
   )
 }