10 Things to Check Before Your Builder Pours the Slab

The concrete slab is the foundation of your entire home. Once it's poured, mistakes are incredibly expensive — or impossible — to fix. Yet many Australian homeowners skip the pre-slab inspection, trusting their builder to get it right.

Here are 10 critical checks you should make before your builder pours the slab.

1. Verify the Site Survey and Set-Out

Check that the slab position matches your approved plans. Measure setbacks from boundaries. Even a 50mm error can cause problems with council compliance. Ask your surveyor for a set-out certificate.

2. Inspect Formwork and Levels

The formwork (boxing) must be straight, level, and properly braced. Check that the finished floor level matches the engineering drawings. Use a string line or laser level to verify.

3. Check Reinforcement Steel (Reo)

Steel reinforcement must match the engineer's specifications exactly. Check:

• Bar sizes (N12, N16 etc.) match the drawings
• Spacing is correct (typically 200mm centres)
• Chairs/spacers maintain correct cover (minimum 40mm from ground)
• Lapping lengths meet standards (40 x bar diameter)
• Edge bars are properly tied

4. Plumbing Rough-In

All under-slab plumbing must be installed and pressure-tested before the pour. Verify:

• Drain positions match the hydraulic plan
• Hot and cold water pipes are in the right locations
• All joints are properly solvent-welded or crimped
• A plumber has signed off on the pressure test

5. Termite Protection

In most Australian states, termite management is mandatory. Check that:

• Chemical barrier has been applied to the slab area
• Reticulation system is installed (if specified)
• Physical barriers (like Termimesh) are correctly placed around penetrations

6. Vapour Barrier (Membrane)

A polyethylene vapour barrier must cover the entire slab area. Ensure:

• 200μm minimum thickness
• Laps are at least 200mm and properly taped
• No tears or punctures
• Turned up at edges

7. Electrical Conduits

Any under-slab electrical conduits must be installed before the pour. Verify that conduit runs match the electrical plan and are properly supported.

8. Drainage and Stormwater

Check that site drainage won't direct water towards the slab. Ag drains should be installed around the perimeter if specified by the engineer.

9. Engineering Inspections

Your structural engineer should inspect the slab before pouring. Request a written inspection report confirming the slab meets the engineering design. This is a legal requirement in most states.

10. Council/Certifier Approval

Your certifier (PCA in NSW, or Building Surveyor in VIC) must inspect and approve the slab before the pour. Do not let your builder pour without this sign-off — it can void your insurance.

Document Everything

Take timestamped photos of every item above. If problems emerge later, these photos are your evidence. HomeOwner Guardian makes this easy with structured checklists and automatic photo timestamping.