The slab and footings carry the whole house, and once concrete is poured, errors are slow and costly to put right. Two of the mandatory critical stage inspections fall at this stage of the build. Here is what gets checked at each one and how to be ready.
Where these inspections sit in the build
In NSW the principal certifier must inspect a new Class 1 home after excavation for footings and before the footings are laid. A second mandatory visit comes before reinforced concrete is cast in place on site, which for most single storey homes means the slab. For the complete list of stages, see Critical stage inspections: what we check and when.
Your structural engineer will often inspect the steel as well. NSW guidance for certifiers makes clear that an engineer's inspection does not take the place of the principal certifier's mandatory inspection. Both may be needed.
The design comes first: site class and engineering
Every slab design starts with the soil. Under the ABCB Housing Provisions, foundations are classified under AS 2870, the Australian Standard for residential slabs and footings. The site class reflects how much the ground can move as it wets and dries. Reactive clay or a filled site needs a stiffer design than stable sand or rock, and some site classes must be designed directly under AS 2870 or by an engineer.
The engineer's slab plan sets the beam sizes, steel, pier depths and any special details. The certifier compares what is built on site with that plan and the approved drawings.
What the footing excavation inspection covers
- the house is set out in the approved position, so the setbacks to boundaries match the plans
- footing trenches and pier holes are in the right places and at the specified widths and depths
- excavations reach the founding material the engineer called for
- trenches are clean, with no loose soil, roots, mud or standing water
- topsoil containing grass roots has been stripped from under the slab area
What the pre-pour inspection covers
This is usually the busier of the two visits. Typical items include:
- Reinforcement: bar and mesh sizes, laps and extra bars at re-entrant corners match the engineering. The Housing Provisions give minimum lap lengths, for example 500 mm for bars up to 12 mm and for trench mesh.
- Bar chairs and cover: the steel sits on chairs so the concrete fully surrounds it. Minimum cover includes 40 mm to unprotected ground and 30 mm where a membrane sits against the ground.
- Vapour barrier: a branded polyethylene underlay of the required impact rating, lapped at least 200 mm, with pipe penetrations taped or sealed and any tears repaired.
- Fill: fill under the slab placed and compacted in layers, with a sand layer on top where needed.
- Termite management: the system for the slab perimeter and service penetrations is installed as specified.
- Edge rebates: where brick veneer will sit on the slab edge, the rebate is formed.
Paperwork that should be ready
The certifier will usually want supporting documents on file, such as:
- the engineer's inspection certificate for the steel
- a surveyor's set-out confirming the house position, if your approval requires one
- details of the termite management system and the installer's certificate
- concrete delivery dockets showing the grade supplied. The deemed-to-satisfy minimum for house slabs is N20, a 28-day strength of 20 MPa, though your engineer may specify more.
NSW guidance notes that only a compliance certificate under the planning legislation carries formal weight. A simple note from a contractor does not give the same protection.
Booking, and what happens when the work falls short
Please book the inspection at least 48 hours ahead, and only once the steel, membrane and penetrations are complete. If something is wrong, the certifier will tell you what needs fixing. Minor items can sometimes be cleared with a certificate or photos. Larger issues need a return visit before the pour.
Do not pour without the inspection. If a mandatory inspection is missed, the principal certifier may be unable to issue an occupation certificate, and fixing that later is difficult.
Planning a new home? See how we handle single storey homes from approval to completion, or request a quote.
Local help across NSW
CertifiBuild certifies Class 1 and Class 10 work in 39 council areas. Local rules on these council pages are a good place to start: Wollondilly Shire Council, Central Coast Council, Waverley Council, Penrith City Council, Fairfield City Council, Hawkesbury City Council.
Suburb pages with local planning notes: Tahmoor, The Entrance, The Oaks, Wadalba, Waverley, Werrington, Wetherill Park, Windsor, Wollongong, Woolooware. You can also browse every service area.
Sources
- Footings, slabs and associated elements (Part 4.2), ABCB Housing Provisions, NCC 2022
- Certifier practice advice: common questions, NSW Government
- MyHome Planner, build stage, NSW Planning Portal