Homeowner guide
Site Class — what does it mean?
Aitken Rowe is a NATA-accredited testing laboratory with labs at Wagga Wagga, Griffith and Albury/Wodonga, and has completed more than 30,000 site classifications. Your soil test comes back with a letter — this explains what it means for your footings.
What drives your classification
Depending on the type of build, your site classification and the footing design that follows may be governed by the reactivity of the underlying clay, shallow bedrock, loose sands, steep slopes or high water tables.
Trees are a major factor too. The tree-induced drying effect can cause excessive ground movement and cracking if the foundations are not designed for it.
A classification is site-specific, not suburb-specific
We have tracked our classifications for several years to build a picture of how soil reactivity varies across the region. Some areas follow clear trends; others are highly unpredictable from one block to the next. That is why the test is done on your lot rather than inferred from the street.
What each class means
Classes under AS 2870. The seasonal movement figures are what the footing system is designed to tolerate.
- A
- Most sand or rock sites, with little or no ground movement from moisture changes.
- S
- Slightly reactive clay sites with only slight ground movement. Footings designed for seasonal movement up to 20mm.
- M
- Moderately reactive clay or silt sites. Footings designed for seasonal movement up to 40mm.
- H1
- Highly reactive clay sites. Footings designed for seasonal movement up to 60mm.
- H2
- Highly reactive clay sites with greater movement. Footings designed for seasonal movement up to 75mm.
- E
- Extremely reactive sites. Footings designed for seasonal movement in excess of 75mm.
- P
- Problem sites — uncontrolled fill, soft clay or silt, loose sands, landslip, mine subsidence, collapsing or erodible soils, abnormal moisture conditions, or large trees next to the footings. Rather than a standard design, footings must be designed by engineering principles. Alternatively the soil can be improved, either by waiting for moisture conditions to normalise or by excavating unsuitable material and replacing it with controlled fill.
- D
- Deep moisture change, shown as a suffix (M-D, H1-D, H2-D, E-D). It puts further strain on the footing system.
What it costs
A standard residential site classification is $1,100 +GST from our Wagga Wagga and Albury/Wodonga laboratories, and $1,350 +GST from Griffith, where the required drilling depth is 4.0m rather than 3.0m. Each includes two boreholes, DCP testing, NATA-accredited laboratory testing and the engineer-signed report.
Discounts apply where testing can be done in one visit, where travel is shared, and where classifications are booked in bulk. For a new subdivision with every lot tested, the price can come down to as low as $500 +GST per lot. Sloping sites, fill and restricted access are quoted individually.
No sewer connection?
If your building site is not connected to council sewer mains you will also need a Land Capability Assessment, sometimes called an Effluent Disposal Assessment, so the septic system is designed for the soil profile underneath it. It can be carried out during the site classification to save a second mobilisation.
Discuss your project
Speak to one of our geotechnical engineers — no call centre, no sales script.
Contact details