AS 2870 is the Australian Standard that connects the ground your home sits on to the slab and footings that support it. It is the standard behind the most time-critical inspection of the entire build: the pre-pour.
What AS 2870 actually means
AS 2870 sets out how residential slabs and footings should be designed for the soil conditions of a particular site. Its central idea is that the ground moves. Reactive clay soils swell when wet and shrink when dry, lifting and lowering across seasons. If a slab is too flexible for that movement, the home above can crack and distort. AS 2870 ties the slab and footing design to a soil classification so the structure is stiff enough to cope.
The standard works alongside the structural engineer's design and the National Construction Code, translating the site's soil report into a buildable slab specification.
Where it applies in your new home
AS 2870 applies to the foundation of almost every new home — the concrete slab and the footing beams beneath it. It governs how deep and wide those footings are, how the slab is reinforced, and how the design responds to the site classification, from stable sand through to highly and extremely reactive clays.
In much of South East Queensland, reactive clay soils are common, which makes the slab design particularly important. A home on highly reactive ground needs a more substantial slab than one on stable soil.
What VG Inspect checks against AS 2870
The pre-pour inspection is where AS 2870 compliance is verified, and timing is everything. It is carried out after the formwork, reinforcement, vapour barrier and underground plumbing are in place, but before any concrete is poured. At that moment an inspector can confirm the footing depths and widths, check the reinforcement size, spacing and cover against the engineered design, verify the vapour barrier is continuous and properly lapped, and confirm the set-out matches the plans.
Because everything is about to be encased in concrete, the report is issued promptly so any issue can be corrected before the pour proceeds. Every finding is documented with photographs.
What can go wrong
Typical pre-pour findings include reinforcement sitting at the wrong height or with inadequate cover, footing beams that are not excavated to the required depth, a vapour barrier that is torn or poorly lapped, and set-out that does not match the design. Each of these affects how the slab will perform over decades.
The reason the pre-pour matters so much is permanence. Concrete is unforgiving — once it is poured, the steel, membrane and footing geometry are locked in. There is no inspecting them later without breaking into the slab.
What AS 2870 does and doesn't cover
AS 2870 covers standard residential slab and footing design within its defined site classifications. Sites with unusual conditions — deep fill, problem soils, steep slopes or abnormal moisture — may require specific engineering beyond the standard's standard solutions. The standard governs the foundation; the framing above is covered by AS 1684, and termite protection by AS 3660.
A VG Inspect QBCC-licensed inspector (QBCC Licence 1318443) carries out every pre-pour inspection personally and reports the same day so nothing holds up your pour unnecessarily. Call 07 3180 8041 or book a pre-pour inspection online.