The overview on this site covers the whole process, from site assessment to warranties. This page zooms in on the part that happens on site. The stage names vary from contract to contract, but the physical order of a house does not, and the principal certifier's mandatory inspections are tied to it.
Before anyone digs
Approval is in place, the contract is signed, the insurance certificate is in your hands and a principal certifier has been appointed. On a knockdown rebuild, the existing house comes down first and the site is cleared. Then the site is set up: fencing, erosion and sediment controls, and access for trucks and machinery.
On a flat block that last part is routine. On a steep Illawarra block it is often the first real engineering decision of the job, because where a truck can stand decides how concrete, steel and spoil move for the rest of the build.
Excavation and footings
The ground is cut to level, and footings are excavated to the depth and size the engineer specified. The certifier must inspect after excavation and before any footings are placed. This is the only moment anyone gets to look at the actual ground the house will sit on, so it is also the moment to confirm it matches what the geotechnical report assumed.
On sloping sites this stage carries most of the uncertainty in a build. Rock that has to be broken, soft ground that has to be dug deeper, groundwater that appears when the cut goes in, and the retaining walls that hold the cut up all show themselves here. That is why a good contract on a difficult block is specific about what the price assumes below ground.
Slab
Formwork, steel reinforcement, plumbing penetrations and termite protection go in, then the concrete is poured. The certifier must inspect before any in-situ reinforced concrete is poured. Once the concrete is in, nobody can check the steel inside it, so this inspection matters more than it looks. On split-level and suspended designs there may be more than one pour, and each one is inspected before the concrete goes in.
Frame
Wall frames, floor frames and roof trusses go up. The frame is what the rest of the house hangs on, and it is checked against the approved plans and the engineer's details. The certifier must inspect before the framework for any floor, wall, roof or other building element is covered. In practice that means before the plasterboard goes on inside.
Roof, cladding, windows and doors
The roof goes on, the external cladding goes up, and the windows and external doors are fitted. At the end of this stage the house can be closed and locked, which is why contracts often call it “lock-up”. From here, most of the remaining work happens inside and out of the weather.
Services and wet areas
Plumbing, drainage and electrical cabling are run through the frame before it is lined. Bathrooms, laundries and other wet areas are then waterproofed. The certifier must inspect before the waterproofing in any wet area is covered, and before any stormwater drainage connections are covered.
Waterproofing and stormwater are the two inspections I would least like an owner to be casual about. Both are cheap to check and very expensive to fix once tiles or backfill are on top of them. On a sloping site the stormwater system also has to get water off the block lawfully, and that is part of the approval, not a detail left for the plumber to decide on the day.
Linings and fit-out
Plasterboard goes up, then the internal doors, skirtings and architraves, the kitchen and joinery, tiling, painting, and the fixtures: taps, lights, power points and appliances. This is the stage most owners picture when they think of building, and it is also where most variations to the contract happen, because it is where selections become real.
Completion and the occupation certificate
The builder finishes the work, defects are listed and fixed, and the site is cleaned up. The certifier carries out a final inspection after the work is complete and before any occupation certificate is issued. If everything is met, the occupation certificate is issued, and you need it to live in the house. Hornsby Shire Council's guidance puts the consequence plainly: missed inspections “may result in the inability to issue an Occupation Certificate.”
Your statutory warranties run from the date the work was completed: six years for major defects and two years for everything else.
How payments should follow the stages
For contracts over $20,000, NSW requires a progress payment schedule, and progress payments must match the work carried out. The deposit is capped at 10 percent. In practice, the stages above are what most payment schedules are built on.
The useful habit is simple: before you pay a stage claim, look at the stage. Is the frame actually up? Has the inspection for that stage been done? A payment schedule that runs ahead of the work leaves you exposed if something goes wrong with the builder, and that is exactly the situation the rule exists to prevent.
The mandatory inspection list
For a house (a class 1 building) and its class 10 structures, such as a garage, the principal certifier's mandatory inspections are:
| When | Stage on this page |
|---|---|
| After excavation for, and before placing, any footings | Excavation and footings |
| Before pouring any in-situ reinforced concrete building element | Slab |
| Before covering any framework for any floor, wall, roof or other building element | Frame |
| Before covering waterproofing in any wet areas | Services and wet areas |
| Before covering any stormwater drainage connections | Services and wet areas |
| After the work is complete and before any occupation certificate is issued | Completion |
Swimming pools add two more: before the pool's reinforced concrete is poured, and once the pool barrier is erected.
- Home construction in the Illawarra, explained: approvals, BASIX, licences, contracts and warranties.
- Choosing a builder: licence and insurance checks: what to verify before you sign or pay.
Sources
Checked on 28 September 2026.
- Hornsby Shire Council, Critical stage inspections and occupation certificates: the mandatory inspections for class 1 and 10 buildings, and the consequence of a missed inspection.
- NSW Government, What certifiers do: mandatory inspections and the occupation certificate.
- NSW Government, Contracts for residential building work: progress payment schedules, the 10 percent deposit, warranty periods.
General information from a builder, not legal or certification advice. Your certifier confirms the inspections that apply to your approval.