A Beginner’s Guide to Site Classification in Australia (AS 2870)
Understand Your Soil Before You Build
Before construction begins, one critical step can determine the success and durability of your entire project: understanding the soil. In Australia, this process is formalised through site classification under AS 2870, the Australian Standard for Residential Slabs and Footings.
At Oz Geos, we specialise in conducting detailed geotechnical investigations that form the foundation of safe, compliant, and cost-effective construction. This guide will help you understand what site classification is, why it matters, and how it affects your build.
What is Site Classification?
Site classification, as defined in AS 2870, is a method for identifying and categorising the reactivity of soil—essentially, how much the soil expands and contracts with changes in moisture. This movement can lead to structural issues like cracking, settlement, or even failure if not properly accounted for in the foundation design.
By classifying a site, engineers can recommend footing systems that are suitable for the specific soil conditions, reducing long-term risk and improving building performance.
The Main Site Classifications in AS 2870
| Classification | Description | Soil Reactivity |
| A | Acceptable | Minimal ground movement |
| S | Slightly reactive clay | Slight ground movement |
| M | Moderately reactive clay | Moderate movement |
| H1 | Highly reactive clay | High movement |
| H2 | Very highly reactive clay | Very high movement |
| E | Extremely reactive site | Extreme movement |
| P | Problem site (e.g. soft fill, rock, poor drainage) | Requires further investigation |
Note: A “P” classification does not mean you can’t build on the site—it simply means further engineering and investigation are needed to determine the appropriate solution.
Why Site Classification Matters
- Foundation Design
Different soils require different types of footings. For instance, a Class M site might be suitable for standard slab-on-ground construction, while an H2 site would need deepened edge beams or piers to accommodate soil movement. - Structural Integrity
Incorrect classification can lead to foundation movement, resulting in cracking and long-term damage to the structure. - Regulatory Compliance
Most local councils and certifiers require a geotechnical report with site classification before issuing building approvals. - Cost Management
Knowing your site class early in the design process helps avoid unexpected expenses and costly changes during construction.
How Site Classification is Performed
The classification process includes several steps, which our team at Oz Geos performs with accuracy and efficiency:
- Borehole drilling to determine soil profile and depth of reactive material
- Soil sampling and classification through on-site and lab testing
- Moisture condition assessments and shrink-swell testing
- Review of site history, drainage, vegetation, and slope
- Groundwater checks to understand seasonal influences
We then prepare a comprehensive geotechnical report that outlines the site class and provides recommendations for footing design based on AS 2870.
Common Misunderstandings About Site Classification
- “My neighbour’s site was Class S, so mine must be the same.”
– Not necessarily. Soil conditions can vary significantly across even small areas. - “A reactive site means I can’t build.”
– You can build on almost any site with the correct engineering. - “P class sites are a problem.”
– P sites just need more investigation. Many urban sites fall into this category due to fill or nearby structures.
Why Choose Oz Geos?
With extensive experience across residential, commercial, and infrastructure projects, Oz Geos offers:
- Accurate and fast geotechnical site classification
- Council-compliant reporting and certification
- Clear foundation recommendations to support engineering design
- Prompt service and communication with builders and developers
Whether you’re building a new home, extending an existing structure, or planning a multi-unit development, we can help you start with confidence.
Get Your Site Assessed Today
If you’re planning to build, don’t guess your site class. Get the facts with a professional geotechnical investigation from Oz Geos.
Contact us for a quote or consultation
Email: info@ozgeos.com.au
Website: www.ozgeos.com.au
