Underpinning Sydney

Older types of houses tend to have shallower brick or stone footings which are generally more susceptible to shrink-swell action – where the ground noticeably contracts and expands depending on moisture levels – which is associated with moderately reactive clay soils. Old brick and stone foundations need special attention because they may become brittle and are therefore considered less suitable for traditional underpinning methods. Areas affected by these conditions include Balmain, Newtown, Marrickville, Strathfield, Cabarita and Five Dock.

Many homes in Sydney’s east are built on sand, and particular care needs to be taken with foundation treatment in these soils because they are non-cohesive soils, susceptible to settlement caused by leaking pipes, erosion, wash out and excavation near the property. Vibrations from neighbouring properties which are being developed may also cause ground disturbance and aggravate wall cracking.  Sandy soils sometimes need permeation grouting in addition to resin treatment to strengthen the ground before a home is re-levelled.  Areas commonly affected by these conditions include Bronte, Bondi, Bellevue Hill, Point Piper, Paddington, Surry Hills and Darlinghurst.

This region tends to be prone to movement associated with shrinkage and expansion of moderate to high reactive clay soils. Common triggers are broken pipes leaking water into the ground which will impact older houses with usually shallower footings.  In a drought, tree roots infiltrate clay pipes seeking moisture. Areas affected by these conditions include Ryde, Epping, Eastwood, Denistone and Asquit

To the west of Sydney, the ground is often formed of highly reactive clay soils which expand and contract aggressively during periods of heavy rain and drought. When paired with older homes, the foundations of brittle and shallow footings offer almost no ability to span over the soft zone on the ground, causing homes to sink.  Brickwork may also feature older style lime mortar which makes walls more susceptible to visible cracking.  As well as sub soil, surface water management is important across larger backyards where rain may collect and run across a property.  Drain repair and drainage solutions may form part of the ground improvement recommendations in areas including Parramatta, Granville, Lakemba, Wentworthville and Cabramatta.

Clay and sandy soil are experienced along the full stretch of the Northern Beaches, with coastal facing properties most affected by erosion. Alluvial patches are common in low lying suburbs including Warriewood, Manly Vale and Cromer which are known flood zones.  These suburbs have a high concentration of silty, clay and sand combination soils which may require homes to have slab foundation  On sloping blocks heavily affected by rains, it may also be important to treat the ground underneath driveways and paths to prevent cracking and trip hazards.  Mainmark works along the peninsula including Manly, Seaforth and extending to Palm Beach.

While many homes in this area of Sydney have been built more recently, the reactive clay soil may still require resin injection to aid with slab repair and fix cracks in concrete driveways. New housing estates are not immune to sinking, particularly when the ground may not have been prepared properly, resulting in the house settling.   Impacted areas include Castle Hill, Kellyville and Rouse Hill.

This area has many larger blocks with single or double-storey homes which may feature old brick and stone foundations. Reactive clay soils can cause these footings to sink over time, and traditional concrete underpinning would be too invasive a process for remediation.  Larger blocks may also be affected by excessive moisture in the ground as trees are removed, which can have a significant impact on foundations. St Ives, Turramurra, Lindfield and Wahroonga are likely impacted.

Sandy soils and rocky ground can allow water to flow under homes and cause home foundations to shift. Some properties may also experience run off or leaks from neighbouring pools which weaken the ground and impact foundations.  Many older sandstone and brick homes also feature brick and stone footings which require special attention and are less likely to be suitable for concrete underpinning if the home needs to be relevelled.  Mosman, Cremorne, Neutral Bay, Kirribilli and Crows Nest all form part of this area.