What to do if your home is subsiding

Foundations are a structurally significant part of any building.

While solid, stable foundations help ensure your home has the support it needs for years to come, buildings can and will move. A fundamental reason for this movement is often due to changes in the ground under your home’s footings.

Many homes experience foundation movement due to changing ground conditions; this is known as subsidence. Regardless of where they live, homeowners share a common goal – to protect their biggest asset. That’s why it is important to identify the signs of subsidence early and act without delay.

The signs to look for

When the ground can no longer support the building, the foundations gradually move downwards, causing the home to sink in one area or across the entire foundation footprint. Every home is different and the signs may not be immediately obvious, so it’s important to know what to look for.

Pay attention to sinking or sloping floors, cracks in walls, paths and driveways as these may be the first signs of structural issues caused by subsidence. Windows and doors becoming jammed or misaligned, skirting boards separating from the wall or the formation of puddles around the perimeter of your home may also indicate foundation ground issues.

When to worry about cracks in walls

While smaller hairline cracks in walls are fairly common and not usually cause for concern, large cracks may appear because the property’s foundation has shrunk or lost its strength, causing all or a part of a building to sink.

Problematic wall cracks typically start at windows, doorways or corners of buildings, and are often zig-zag/stepped cracks in brickwork which usually follow the mortar lines. They are usually wider than 5mm (or half a centimetre) or big enough for you to insert your little finger in them.

Be aware of conditions beneath your foundations

Understanding what’s happening in the ground beneath your home, including the type of soil your house is built on, may be the key to identifying the cause of subsidence and possible solutions.

This is especially important for homeowners in areas where soil is known to be unstable. Houses built on loosely packed soils, old landfill sites, sand and reactive clays can be particularly affected by seasonal or extreme weather conditions, drought and floods. Historical mining activity can also impact properties in certain areas, like this home in New South Wales.

Structural problems often result from varying moisture levels in reactive clay soil which can shrink, or crack and shift during hot weather, and then expand during wetter seasons. Other problems can arise due to tree roots removing moisture from the soil or penetrating pipes to create underground leaks. Poor drainage beneath a concrete slab was the issue identified as the likely cause of the subsidence of a sunroom patio in a brick veneer home. The homeowner worried that the entire building would need to be replaced. Fortunately, after addressing the underlying drainage issues, the home was re-levelled within a few hours, at a fraction of the cost of replacement or other solutions.

Seismic activity such as earthquakes can cause soil to temporarily lose stability, known as liquefaction, which may then lead to subsidence. After a major earthquake in New Zealand, the owner of a large family home near Wellington noticed cracks appearing around door frames and along the ceiling joint as well as plaster detaching. Using a precise application method, the ground under the slab was treated via tiny injection points, to strengthen the ground. The cracks have since closed and the doors and windows have come back into alignment.

Subsidence can also occur when nearby excavation, tunnelling or drilling activity causes vibration and ground movement, impacting foundation stability. Whether it’s a neighbour adding an inground pool, new developments in the area or major infrastructure projects underway, it’s important to understand the cause of subsidence to treat the problem effectively. Remediation solutions can usually be applied with minimal impact, to protect the integrity of even the most fragile structures, like a heritage church in central Sydney where the foundations were impacted by deep excavation during a nearby infrastructure development project.

Simple and affordable remediation solutions

Today, there are innovative solutions available to help address structural issues which are non-invasive, fast and cost effective when compared to traditional underpinning methods. Homes can usually be re-levelled within just a few hours without the need for occupants to vacate the property or move furniture.

Ask an expert

If signs of subsidence have appeared, consult structural and geotechnical engineers or ground engineering experts. Mainmark has treated more than 11,000 sites throughout Australasia, from single-storey homes to large commercial buildings. The Teretek® engineered resin injection solution uses a “key-hole” approach, has been extensively tested for local conditions and comes with a 50-year product warranty, providing long-term peace of mind.

For more information and advice about ground issues and remediation solutions, contact Mainmark on 1800 623 312 in Australia, 0800 873 835 in NZ or visit mainmark.com.


By James O’Grady

James O’Grady is the Sales and Business Development Manager at Mainmark. He is a civil engineer with 25 years’ experience in structural engineering, construction materials and ground treatment.