Why is a Soil Test Required
Before a new home, extension, or significant renovation can proceed to Building Approval, a geotechnical soil test (also known as a site classification report) is required. This report identifies the soil type, bearing capacity, and reactivity of your site so that the slab and footing design can be engineered to suit local ground conditions. Engineers will then use the site classification to determine the slab and footing requirements for your project. The NCC and Australian Standard AS 2870 – Residential Slabs and Footings, require that all residential building sites be classified prior to construction to ensure structural stability and minimise long-term movement or cracking. However, in some instances where a renovation does not change the overall footprint of your home or change the location of load bearing walls – a soil test may not be required.
What the Soil Test Involves
A qualified geotechnical engineer or soil technician will visit your property and drill one or two small boreholes (typically 75mm in diameter) to collect soil samples. The samples are then laboratory-tested to determine soil composition, moisture content, and shrink-swell potential. The resulting report assigns your site a classification (e.g. Class A, S, M, P, H1, H2, or E) this classification indicates how reactive the soil is to moisture changes. This is essential for your structural engineer to develop safe and compliant footing and slab details.
When a Soil Test is Needed
A soil test is required for:
- All new dwellings before structural engineering can commence.
- Extensions or additions where new foundations, footings, or slabs are proposed.
- Rebuilds or knockdown-rebuilds, even on previously developed sites (as soil conditions can change over time).
If you're only undertaking minor internal renovations or work that doesn't involve new footing or slab construction, a soil test is generally not required.
Guidance from Realex Design
At Realex Design, we’ll advise when your project requires a soil test and can arrange this through our partnered geotechnical engineers. We’ll ensure your design and documentation align with the soil classification results to meet NCC and Australian Standards, supporting a safe and durable build from the ground up.
At Realex Design, we specialise in raise and build under projects, helping homeowners make the most of their space while preserving the character of their property. Our team works closely with you to ensure that the final result enhances both the functionality and style of your home. Whether you're aiming to expand, renovate, or modernise, we can guide you through the process, creating a home that meets your needs and exceeds your expectations.