Understanding Site Classification Reports for Foundation Design
A site classification report is more than a single letter grade — it’s a genuine technical document your engineer relies on for every subsequent design decision.
What Produces a Classification
A site classification is the output of a geotechnical assessment — physical soil testing at your specific site, analysed against the criteria set out in AS 2870, resulting in a formal classification (A through E, or P) documented in your soil report. See our site classification guide for what each rating means.
The Testing Behind the Report
Testing typically involves boreholes or similar sampling at multiple points across the site, analysing soil type and reactivity characteristics at different depths. This physical, site-specific testing is what makes the resulting classification genuinely reliable, as opposed to a generic assumption based on the surrounding area.
Report Structure
A typical report includes the site classification itself, a description of the soil profile found at each test location, any specific site factors identified (fill, groundwater, slope), and engineering parameters your structural engineer needs for detailed design calculations. See our how to read a soil report guide for a homeowner-friendly walkthrough.
How Your Engineer Uses It
Your structural engineer uses the classification report as the primary input for foundation system selection and detailed design — slab type, thickness, reinforcement, and beam sizing all follow from this data combined with your building’s specific loads. Without it, foundation design is effectively working blind.
Keeping Your Report Current
A classification report can become outdated if significant time has passed or the site has been disturbed (earthworks, fill added or removed) since testing. If either applies to your project, it’s worth discussing with your engineer whether the existing report remains reliable or a new assessment is warranted.
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Frequently Asked Questions
How long is a site classification report valid?
There’s no fixed universal expiry, but reports can become outdated if significant time has passed or the site has been disturbed since testing — worth discussing with your engineer if either applies.
Can I use a classification report from a different property?
No — classification is site-specific, and conditions can vary meaningfully even within a single street or block, particularly where fill has been used unevenly.
What's included in a site classification report beyond the letter grade?
A description of the soil profile at each test location, any specific site factors identified, and engineering parameters your structural engineer needs for design calculations.
Does every project need its own new classification report?
For compliant residential slab work, yes — a current, site-specific report is required, not a generic or borrowed assessment.
Who produces a site classification report?
A geotechnical engineer or qualified soil testing company, based on physical testing carried out at your specific site.
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