A site classification answers one question: how much the soil near your footings will shrink and swell. The answer comes from soil taken near where the footings will sit, then tested in a laboratory. The report places the site in an AS 2870 class, from S (slightly reactive) through M, H1 and H2, with E and P for extreme and problem sites. QBCC guidance says reactive clay can cause structural damage and that drawings must show the site classification. Local building inspectors already publish advice on cracks in Ipswich homes from clay and slab heave. A correct classification lets the engineer design footings that allow for that movement from the start.
There is a second question that a 2 m borehole cannot answer. Ipswich's planning scheme includes a mining overlay that maps mining influence areas, surface disturbance and land affected by underground mining. The history behind it is real. At Collingwood Park, two decommissioned underground coal mines caused subsidence in December 1988 and April 2008 that damaged houses, although the state says monitoring shows the ground there is currently stable. That is a Collingwood Park fact and says nothing about your lot. It does explain why you should check the overlay first. If your lot is mapped, approval may need a specialist mining assessment as well as the AS 2870 classification. Knowing this early helps you avoid booking the wrong report or finding the gap late in approval.
Flooding is the third factor on many central Ipswich jobs. The Bremer River at Ipswich peaked at 19.40 m in January 2011 and at 16.72 m in February 2022, and homes were extensively inundated in 2022. Owners who raise or rebuild after a flood need ground information for the new footings, and they should check the council flood overlay for their lot. The housing stock adds its own layer. Many Ipswich timber houses date from the building boom between the 1850s and World War I, and some are heritage-listed. Restumping, raising or extending one of these homes means new footings, and heritage or character controls in Ipswich City Plan 2025 may also apply. Old and new footings can behave differently on the same block.
In Ipswich, the mining overlay is a separate question from soil reactivity - and we are upfront that a 2 m site classification is not a mining assessment.
