diff --git a/packages/core/src/store/use-scene-surface-holes-defaults.test.ts b/packages/core/src/store/use-scene-surface-holes-defaults.test.ts
new file mode 100644
index 0000000000..d320cedecc
--- /dev/null
+++ b/packages/core/src/store/use-scene-surface-holes-defaults.test.ts
@@ -0,0 +1,147 @@
+import { beforeEach, describe, expect, test } from 'bun:test'
+import type { AnyNode } from '../schema'
+import useScene from './use-scene'
+
+// Third-party exporters (scanning apps, IFC hand-offs) can legitimately write a
+// slab or ceiling without `holes` / `holeMetadata` / `autoFromWalls`: the schema
+// declares defaults for them. The opening sync and the public viewer read those
+// fields on the raw node, so a missing `holes` threw
+// "Cannot read properties of undefined (reading 'map')" and the scene never
+// rendered. Doors and windows are already zod-parsed on load; this covers
+// slabs and ceilings the same way.
+describe('scene load applies surface hole defaults', () => {
+  beforeEach(() => {
+    useScene.setState({
+      nodes: {},
+      rootNodeIds: [],
+      dirtyNodes: new Set(),
+      collections: {},
+    } as never)
+    useScene.temporal.getState().clear()
+  })
+
+  const base = {
+    site_test: {
+      object: 'node',
+      id: 'site_test',
+      type: 'site',
+      parentId: null,
+      visible: true,
+      metadata: {},
+      children: ['building_test'],
+    },
+    building_test: {
+      object: 'node',
+      id: 'building_test',
+      type: 'building',
+      parentId: 'site_test',
+      visible: true,
+      metadata: {},
+      children: ['level_test'],
+    },
+    level_test: {
+      object: 'node',
+      id: 'level_test',
+      type: 'level',
+      parentId: 'building_test',
+      visible: true,
+      metadata: {},
+      level: 0,
+      children: ['slab_bare', 'ceiling_bare'],
+    },
+  }
+
+  test('a slab and a ceiling written without holes load with empty hole arrays', () => {
+    useScene.getState().setScene(
+      {
+        ...base,
+        slab_bare: {
+          object: 'node',
+          id: 'slab_bare',
+          type: 'slab',
+          parentId: 'level_test',
+          visible: true,
+          metadata: {},
+          polygon: [
+            [0, 0],
+            [4, 0],
+            [4, 3],
+            [0, 3],
+          ],
+          elevation: 0.05,
+        },
+        ceiling_bare: {
+          object: 'node',
+          id: 'ceiling_bare',
+          type: 'ceiling',
+          parentId: 'level_test',
+          visible: true,
+          metadata: {},
+          polygon: [
+            [0, 0],
+            [4, 0],
+            [4, 3],
+            [0, 3],
+          ],
+        },
+      } as unknown as Record<AnyNode['id'], AnyNode>,
+      ['site_test' as AnyNode['id']],
+    )
+
+    const slab = useScene.getState().nodes['slab_bare' as AnyNode['id']]
+    expect(slab?.type).toBe('slab')
+    if (slab?.type !== 'slab') return
+    expect(slab.holes).toEqual([])
+    expect(slab.holeMetadata).toEqual([])
+    expect(slab.autoFromWalls).toBe(false)
+    expect(slab.polygon).toEqual([
+      [0, 0],
+      [4, 0],
+      [4, 3],
+      [0, 3],
+    ])
+
+    const ceiling = useScene.getState().nodes['ceiling_bare' as AnyNode['id']]
+    expect(ceiling?.type).toBe('ceiling')
+    if (ceiling?.type !== 'ceiling') return
+    expect(ceiling.holes).toEqual([])
+    expect(ceiling.holeMetadata).toEqual([])
+  })
+
+  test('existing holes and metadata are kept as written', () => {
+    useScene.getState().setScene(
+      {
+        ...base,
+        level_test: { ...base.level_test, children: ['slab_holed'] },
+        slab_holed: {
+          object: 'node',
+          id: 'slab_holed',
+          type: 'slab',
+          parentId: 'level_test',
+          visible: true,
+          metadata: {},
+          polygon: [
+            [0, 0],
+            [4, 0],
+            [4, 3],
+            [0, 3],
+          ],
+          holes: [
+            [
+              [1, 1],
+              [2, 1],
+              [2, 2],
+              [1, 2],
+            ],
+          ],
+          holeMetadata: [{ source: 'manual' }],
+        },
+      } as unknown as Record<AnyNode['id'], AnyNode>,
+      ['site_test' as AnyNode['id']],
+    )
+    const slab = useScene.getState().nodes['slab_holed' as AnyNode['id']]
+    if (slab?.type !== 'slab') throw new Error('slab expected')
+    expect(slab.holes).toHaveLength(1)
+    expect(slab.holeMetadata).toEqual([{ source: 'manual' }])
+  })
+})
diff --git a/packages/core/src/store/use-scene.ts b/packages/core/src/store/use-scene.ts
index 5e45cf7402..18e30a8f1a 100644
--- a/packages/core/src/store/use-scene.ts
+++ b/packages/core/src/store/use-scene.ts
@@ -178,6 +178,22 @@ function normalizeWindowNode(node: Record<string, unknown>) {
   return parsed.success ? { ...node, ...parsed.data } : null
 }
 
+// Slabs and ceilings written by third-party exporters (scanning apps, IFC
+// hand-offs) can legitimately omit `holes` / `holeMetadata` / `autoFromWalls`:
+// the schema gives them defaults. The opening sync and the public viewer read
+// those fields on the raw node, so a missing `holes` throws
+// "Cannot read properties of undefined (reading 'map')" and the scene never
+// renders. Only the hole fields are filled here — a full zod parse would also
+// default `thickness`, which the vertical-model migration below must still see
+// as absent on legacy solids.
+function normalizeSurfaceHoleFields(node: Record<string, unknown>) {
+  const holes = Array.isArray(node.holes) ? node.holes : []
+  const holeMetadata = Array.isArray(node.holeMetadata) ? node.holeMetadata : []
+  const autoFromWalls =
+    node.type === 'slab' && node.autoFromWalls === undefined ? { autoFromWalls: false } : {}
+  return { ...node, holes, holeMetadata, ...autoFromWalls }
+}
+
 function normalizeShelfNode(node: Record<string, unknown>) {
   const sanitized = {
     ...node,
@@ -826,6 +842,10 @@ function migrateNodes(nodes: Record<string, any>): {
       }
     }
 
+    if (node.type === 'slab' || node.type === 'ceiling') {
+      patchedNodes[id] = normalizeSurfaceHoleFields(patchedNodes[id] ?? node) as AnyNode
+    }
+
     // Dormers originally rendered one inline parametric window. Promote that
     // default to a real hosted WindowNode so additional windows can use the
     // regular window tool and inspector without changing the old appearance.