What is Compare My Build?

An interactive comparison platform for home buyers to evaluate builders, plans, and inclusions in their region side-by-side.

What should I check at the slab stage?

Check slab dimensions against the plans, slab level (use a spirit level), room positions (internal wall markings), opening positions (doors, windows), slab thickness (visible at the edge), cracking, drainage provisions, plumbing rough-in (toilets, sinks, drains) and electrical conduits. Take photos of everything and document any issues.

When should I inspect the slab?

Inspect the slab after it's poured and cured (typically 7–14 days after pouring), and before the frame stage begins. Once the frame is erected, you can't see the slab surface. Arrange the inspection with your builder. Take photos — they're your record if issues arise later.

Free for home$Spot costly upgradesCompare real builder

Free for home buyers$Spot costly upgradesCompare real builder inclusions

Home›Build Knowledge Hub›Building Process & Construction Stages

Building Process & Construction Stages

Slab Stage: What to Check, Common Issues & How to Inspect

What happens at slab stage, what to inspect and common issues to look for.

5 min read·Compare My Build — Independent Resource· Updated July 2026

Cost estimates only: Any building or upgrade figures in this guide are indicative, not fixed prices or quotes. Costs and inclusions vary by project, supplier, location and time. Confirm current written prices and specifications directly with your builder, suppliers and relevant trades.

Key Takeaways

The slab is your home's foundation — errors here are expensive to fix
Check slab dimensions, level, cracking, drainage provisions and plumbing rough-in
Hairline cracks are normal; structural cracks (wide, displacement) are not
Verify the slab matches the plans — room sizes, openings, positions
Take photos and document any issues before the frame stage begins

The slab (base stage) is your home's foundation — everything is built on it. While slab errors are relatively rare with reputable builders, they're expensive to fix if they occur. A thorough slab inspection before the frame stage begins helps catch issues early. This guide covers what to check, common issues and what to document.

What to Check

Slab dimensions — measure the slab perimeter and compare to the plans
Slab level — use a spirit level to check the slab is level (minor variations are normal)
Room positions — check that internal wall positions are marked and match the plans
Opening positions — check door and window openings are in the right place
Slab thickness — check the slab edge for consistent thickness (visible at the slab edge)
Cracking — check for cracks (see below for what's normal vs concerning)
Drainage provisions — check that plumbing pipes and drainage are in the right place
Plumbing rough-in — check that plumbing rough-in (toilets, sinks, drains) is positioned correctly
Electrical conduits — check that electrical conduits through the slab are in place
Edge form — check that the slab edge is clean and straight
Step-downs — if your home has level changes, check the step-downs are correct

Cracking: Normal vs Concerning

Concrete slabs can develop cracks. Some are normal; others are concerning:

Hairline cracks (less than 1mm wide) — normal; caused by concrete shrinkage during curing; not a structural concern
Plastic shrinkage cracks — surface cracks that appear during curing; typically not a structural concern
Cracks 1–3mm wide — monitor; may or may not be a concern depending on location and pattern
Cracks over 3mm wide — potentially concerning; have a structural engineer assess
Cracks with displacement (one side higher than the other) — concerning; indicates slab movement
Pattern cracks (spider web or diagonal) — may indicate underlying issues; have assessed

Watch Out

If you see cracks over 3mm wide, cracks with displacement (one side higher than the other), or pattern cracks (spider web or diagonal), raise it with your builder immediately. These may indicate slab movement or structural issues that need to be assessed. Take photos and measurements. If the builder dismisses your concerns, consider hiring a structural engineer to assess.

Common Slab Issues

Wrong dimensions — slab is smaller or larger than the plans
Wrong room positions — internal wall positions don't match the plans
Wrong opening positions — door or window openings in the wrong place
Plumbing rough-in errors — toilets, sinks or drains in the wrong position
Insufficient thickness — slab is thinner than specified
Poor finish — slab surface is rough, uneven or has excess laitance (surface dust)
Missing provisions — drainage, plumbing or electrical conduits missing

What to Document

Photos of the entire slab (wide shots from multiple angles)
Photos of any cracks (with a ruler or coin for scale)
Photos of plumbing and electrical provisions
Notes on any issues or concerns
Measurements if anything doesn't match the plans

Questions to Ask Your Builder

Can I inspect the slab before the frame stage begins?
Do the slab dimensions and room positions match the plans exactly?
Are there any cracks, and if so, are they hairline (normal) or structural (concerning)?
Are all plumbing and electrical rough-ins in the correct positions?

Common Mistakes to Avoid

Not inspecting the slab before the frame goes up — you can't see the surface after that
Ignoring cracks over 3mm or cracks with displacement — these may indicate structural issues
Not verifying plumbing rough-in positions — moving pipes after the frame is expensive
Forgetting to take photos — they're your record if issues arise later

Builder Tips

Inspect the slab after curing (7–14 days) and before the frame stage begins
Hairline cracks (under 1mm) are normal; cracks over 3mm or with displacement need assessment
Check that room positions, openings and plumbing rough-ins match the plans exactly
Take photos of the entire slab, any cracks (with a ruler for scale), and all provisions

Frame Stage: What to Check

The next stage — the most important inspection.

Read the Guide