Understanding Your Soil Classification in Queensland: What AS2870 Site Classes Mean for Your Build
If you’re planning a new home or extension in Queensland, understanding your Soil Classification in Queensland is a crucial first step. When you receive a soil report, it often lists a site classification like Class A, S, M, H1, H2, E, or P. While this may seem confusing at first, it’s one of the most important pieces of information for your build. Proper classification ensures your foundations are safe, durable, and compliant with Australian standards.
At Australian Soil Investigations, we provide expert soil testing services and geotechnical drilling services across the Sunshine Coast, Bundaberg, Gympie, Hervey Bay, and South East Queensland. Our detailed reports give you and your builder the confidence to make informed decisions before construction begins.
What Is a Soil / Site Classification?
A site classification assesses how the soil beneath your proposed building behaves over time, especially as moisture levels change. It primarily looks at:
Soil reactivity – how much the soil shrinks and swells with changes in moisture.
Ground movement potential – how much the land may shift or settle.
Soil bearing capacity – the amount of weight the soil can safely support.
This classification forms the foundation for your engineer’s footing and slab design. Highly reactive sites typically need more robust foundations, while stable sites allow simpler, more cost-effective designs. Every standard soil test from Australian Soil Investigations includes a class rating based on these factors in line with AS2870.
How Your Site Class Is Determined
Determining your site classification involves several steps:
On-site investigation and drilling
Our technicians drill boreholes within your building footprint, logging soil layers, slope, fill, and visible risks. This ensures no detail is overlooked.Soil sampling and laboratory testing
Samples are tested for moisture content, clay reactivity (Atterberg limits), density, compaction, and particle size distribution (sand, silt, clay). Accurate lab testing is key to a reliable classification.Consideration of site factors
Local vegetation, drainage, slope, fill depth, and nearby structures all influence your site class and foundation recommendations.Assignment of AS2870 site class
Using AS2870 criteria, a qualified soil professional assigns a class (A, S, M, H1, H2, E, or P) and provides design parameters your engineer will use for footing and slab construction.
The final soil report is essential for your builder and engineer to design safe and compliant foundations.
A Quick Guide to AS2870 Site Classes
Here’s a general overview of AS2870 classifications:
Class A – Stable sand or rock
Class A refers to sites with stable sand or rock, where minimal ground movement is expected due to moisture changes. These soils are very reliable for construction, allowing simple and cost-effective footing and slab designs. Builders typically face fewer challenges, and foundations generally require standard engineering without special reinforcement.
Class S – Slightly reactive clay
Class S – Slightly reactive clay sites refers to soil that experiences only minor movement as moisture levels change. These sites are generally stable with small amounts of shrinkage or swelling. Footings on Class S soil may require slight allowances for movement, making foundation designs moderately simple and more cost-effective than highly reactive clay sites.
Class M – Moderately reactive clay or silt
Class H1 – Highly reactive clay
Class H1 – Highly reactive clay refers to soil that undergoes significant movement due to changes in moisture levels. This type of clay swells when wet and shrinks when dry, which can cause foundation cracking or structural stress if not properly managed. Homes on H1 sites require reinforced footings and carefully engineered slab designs to ensure long-term stability and safety.
Class H2 – Very highly reactive clay
Class E – Extremely reactive
Class E – Extremely reactive soils are highly unstable and pose a serious risk of ground movement due to moisture changes. These sites experience extreme shrink-swell behavior, which can cause significant cracking or shifting in foundations if not properly managed. Building on Class E soil requires custom-engineered footings and slabs designed specifically to accommodate the high movement potential, ensuring long-term structural stability..
Class P – “Problem” sites
Tip: The progression from A → P reflects increasing soil reactivity and complexity, typically increasing foundation costs.
Why Your Soil Classification Matters for Your Build
Your classification provides insight into:
Risk of cracking and movement – Higher classes like H2, E, and P indicate a greater risk of slab and wall movement if foundations aren’t engineered correctly.
Foundation complexity and cost – Reactive or problem sites often require deeper beams, more concrete, and additional reinforcement.
Importance of drainage and site preparation – Managing moisture through proper drainage, landscaping, and grading is critical on reactive soils.
Extensions and renovations – Your classification helps engineers design new footings that integrate with or isolate from existing structures.
For more on what to expect from a soil test before you build, see The Residential Soil Test: What to Expect Before You Build. This guide complements your site classification by explaining the full testing process and how it informs your build decisions.
How Australian Soil Investigations Can Help
With over 27 years of experience in soil testing services and geotechnical drilling services, Australian Soil Investigations ensures your site assessment is accurate and reliable. Our services include:
Comprehensive on-site investigations – Boreholes, sampling, and logging tailored to your footprint and wastewater needs.
Laboratory testing to Australian standards – Assessing moisture, plasticity, density, and more for precise classification.
Clear reporting with AS2870 site class – Reports include design parameters your engineer can use directly.
Expert guidance and interpretation – Our team explains your report in plain language and liaises with builders, engineers, or architects.
Our goal is to provide clarity and confidence that your home or extension will sit on foundations designed specifically for your soil conditions.
Ready to Understand Your Soil Classification?
If you want peace of mind before building, or need a detailed soil report for your Queensland property, Australian Soil Investigations can help.
Contact Us Today:
Australian Soil Investigations
Phone: 0428 310 453
Email: aussiesoil@yahoo.com.au
We provide residential and commercial soil testing, site investigations across South East QLD, geotechnical drilling services, and on-site effluent system design. Request a quote, discuss your site classification, or book a soil test today – and build your home with confidence knowing exactly what lies beneath your feet.