The impact of prolonged dry weather on building foundations

After months of little to no rainfall, many Australian regions are experiencing drier than average ground conditions. This weather pattern looks likely to continue, with the Bureau of Meteorology predicting drier than average Summer conditions, following one of the driest winters on record for large parts of the country. Coinciding with this dry spell are increased reports of wall cracks in suburban homes.

This trend is unsurprising; last year’s record-breaking UK summer affected many building foundations as lack of rain caused water from subsoils to dry out, resulting in shrinkage. This created a subsidence surge.

Why subsidence occurs in dry conditions

Subsidence occurs when the ground changes, causing the foundation of a home to gradually settle in one area or across the entire footprint. Many Australian homes are built on sandy or reactive clay soils which shrink and swell in response to moisture levels.

The combination of significant drought conditions, with occasional heavy rainfall, can result in shifting foundations as varying moisture levels cause clay soil beneath the home to shrink or swell, which can cause movement.

When buildings become un-level due to subsidence, it can result in significant and expensive damage so it is important to recognise the signs of subsidence early and act without delay.

Often one of the first indicators of foundation subsidence is cracks in walls appearing or getting significantly wider. Remember, not all wall cracks are the same; the type, size and location of cracking is important to consider when identifying the likely cause. Likewise, every home is different and the signs may not be immediately obvious or limited to wall cracks, so it helps to know what else to look for:

  • sinking or sloping floors
  • windows and doors becoming jammed or misaligned
  • skirting boards separating from the wall
  • puddles around the perimeter of the home.

There is more than one solution for subsidence

Once the underlying cause has been identified, homeowners often assume the only solution is to ‘underpin’ their home without realising there are alternative and far less disruptive methods for addressing foundation issues.

When a Sydney homeowner observed a gap at the base of the wall inside their house, they worried that the building foundations were sinking. Mainmark technicians were able to treat the issue by applying their Teretek® resin injection solution from the exterior of the building via small penetrations, avoiding any need for excavation or damage to the home.

Ground improvement by non-invasive resin injection has minimal impact to the structure of the home, and is generally more cost effective than traditional underpinning methods. It has less impact on the surrounds of the building, including gardens, and is environmentally inert.

A heritage café in Melbourne had suffered differential settlement which caused a double brick wall at the western end of the building to rotate by 30mm, resulting in the appearance of stress cracks on the wall and separation at the wall openings on the two transverse walls.

The issue occurred when tree roots from a row of heritage listed elm trees growing in close proximity to the café had removed moisture from the reactive clay soil during prolonged dry periods, causing localised subsidence. The problem was remediated with no impact on the structural integrity of the heritage building or damage to the protected trees.

If the signs of subsidence appear, consult structural and geotechnical engineers or ground engineering experts. Building movement can be caused by other underlying or site specific issues which require a professional assessment and working knowledge of the local area.

Mainmark has treated more than 11,000 sites throughout Australasia, from single-storey homes to large commercial buildings. For more information and advice about ground engineering issues and remediation solutions, contact Mainmark on 1800 623 312 in Australia or 0800 873 835 in NZ, or visit www.mainmark.com.


Laurie Andrews MainmarkBy Laurie Andrews

Laurie Andrews is Mainmark’s Business Development Manager for NSW & ACT. Laurie is a qualified civil and structural engineer with nearly 30 years experience working in the construction and engineering industry.