Slab-on-Grade Inspection

Subgrade must be compacted and level. Vapor barrier (minimum 10-mil polyethylene) required under all inhabited slabs. Gravel base recommended.

1. Check subgrade compaction — firm, no soft spots when walking

2. Verify gravel base depth (typically 4" of compacted gravel)

3. Check vapor barrier coverage — 10-mil poly minimum, covering entire slab area

4. Verify vapor barrier overlaps at seams — minimum 6" overlap, taped

5. Check that vapor barrier extends up at edges (turned up foundation wall)

6. Verify no punctures or tears in vapor barrier

7. Check for plumbing and electrical rough-ins protruding through vapor barrier — sealed around penetrations

- No vapor barrier (moisture migrates through slab — ruins flooring, causes mold)

- Vapor barrier punctured by foot traffic or rebar chairs

- Insufficient overlap at seams (moisture pathway)

- Subgrade not compacted (slab cracks from settlement)

- No gravel base (drainage issues)

- Vapor barrier not turned up at edges

Minimum 3-1/2" thick for residential slabs per IRC R506.1 (most contractors pour 4" as standard practice). Thicker at edges and under bearing walls. Wire mesh or rebar reinforcement per plans.

1. Check slab thickness — minimum 3-1/2" for residential per IRC R506.1, 4" is standard practice (verify with depth gauge or check at edges)

2. Verify edge thickening (turned-down edge) at perimeter — typically 12" deep

3. Check reinforcement — wire mesh (6x6 W1.4/W1.4) or rebar per plans

4. Verify reinforcement is positioned at mid-depth of slab (supported on chairs)

5. Check for additional reinforcement under bearing walls

6. Verify anchor bolts are positioned for wall plates (1/2" at 6' OC, 7" embedment)

7. Check control joint plan — joints at proper spacing (24-36 times slab thickness in feet)

- Slab too thin — cracks under load

- No edge thickening — slab cracks at perimeter

- Mesh on ground instead of at mid-height (provides no reinforcement)

- Missing reinforcement under bearing walls

- Anchor bolts in wrong locations

- No control joint plan — random cracking