House subsidence occurs when the ground beneath a home sinks or loses strength, causing part of the building’s foundations or footings to move downwards. This can result in cracked walls, uneven floors, sticking doors and windows, sinking concrete and other signs of foundation movement.

Subsidence can affect one localised section of a house or extend across a larger part of the building footprint.

Common signs of house subsidence include:

• New or widening cracks in walls
• Stepped cracks through brickwork or mortar joints
• Uneven, sloping or sinking floors
• Doors and windows that stick or no longer align
• Gaps around window frames, doors or skirting boards
• Separation between an extension and the main house
• Sunken concrete paths, driveways or floor slabs
• Cracks that reappear after being repaired

One symptom alone does not confirm subsidence. A professional assessment is needed to determine whether the movement is active and identify what is causing it.

No. Small cracks can develop because of normal building movement, temperature changes, drying plaster or minor settlement.

Cracks are more concerning when they continue to widen, repeatedly return after repair, follow a stepped pattern through brickwork or appear alongside uneven floors, sticking doors or other signs of foundation movement. Significant or progressive cracking should be professionally investigated before cosmetic repairs are completed.

No. Small cracks can develop because of normal building movement, temperature changes, drying plaster or minor settlement.

Cracks are more concerning when they continue to widen, repeatedly return after repair, follow a stepped pattern through brickwork or appear alongside uneven floors, sticking doors or other signs of foundation movement. Significant or progressive cracking should be professionally investigated before cosmetic repairs are completed.

Subsidence occurs when the supporting ground sinks or loses strength, causing the foundations above it to move downwards.

Settlement is the compression of soil beneath the weight of a building. Some initial settlement can occur after construction, but uneven or continuing settlement may damage the home.

Heave is upward movement caused by soil expanding or swelling beneath the foundations, often because of moisture changes in reactive clay. An assessment is needed to distinguish between these problems before repairs begin.

Yes. Many subsiding houses can be repaired once the cause, location and extent of the movement have been identified.

Depending on the property, the repair may involve improving the supporting ground, filling voids, strengthening or re-supporting foundations and carefully re-levelling the affected section of the house. Plumbing leaks, drainage problems or other contributing issues may also need to be corrected as part of the overall solution.

No. Traditional underpinning is not the only way to repair a subsiding house.

Depending on the foundation design and ground conditions, possible treatments may include resin injection underpinning, ground improvement, void filling, foundation re-support, slab lifting or controlled house re-levelling. More extensive structural or ground problems may require traditional underpinning or another engineered solution.

The correct method depends on what is causing the movement rather than the visible cracks alone.

Small injection points are created near the affected foundations. An engineered polyurethane resin is then injected into the ground at controlled locations and depths.

As the resin expands, it can fill voids, compact or strengthen weak ground and restore support beneath the foundations. Where the structure and ground conditions allow, continued controlled injection may also help raise the affected section of the house towards the required level.

In many cases, subsidence repair can include controlled house re-levelling. Once support beneath the foundations has been restored, the affected section may be carefully raised towards its required position.

The amount of lift that can safely be achieved depends on the building’s construction, condition, foundation type, ground conditions and extent of movement. Complete level correction is not appropriate or achievable for every property.

Yes. A concrete floor or slab can sink when weak ground, settlement or voids beneath it result in a loss of support.

Depending on the cause, resin injection or another slab-lifting treatment may be used to fill the underlying void, improve support and carefully raise the affected concrete. A site assessment is required to determine whether the floor slab, the building foundations or both have moved.

The cost of repairing house subsidence varies significantly between properties. Important factors include:

• The size of the affected area
• The severity of the foundation movement
• The depth and condition of the supporting ground
• The type of foundations or footings
• Site access
• The repair method required
• Whether void filling or re-levelling is needed
• Whether plumbing, drainage or structural repairs are also required

An on-site assessment is needed before an accurate subsidence repair quote can be provided.

The timeframe depends on the size and complexity of the problem.

Some targeted resin injection projects can be completed in as little as a day. Larger properties, deeper ground problems or projects requiring additional structural, drainage or plumbing work may take longer.

Mainmark will outline the proposed treatment area and expected timeframe after assessing the property.

Homeowners can often remain in their house during targeted resin injection work because the treatment is generally completed through small injection points and requires much less excavation than traditional underpinning.

Temporary access restrictions may apply around the treatment area. Mainmark will advise whether any property-specific safety, access or accommodation arrangements are required before work begins.

Untreated subsidence may allow foundation movement and associated building damage to continue. Cracks may widen, floors may become more uneven and doors or windows may become increasingly difficult to operate.

However, not every crack indicates active subsidence. The priority is to determine whether the movement is continuing, identify its cause and address any drainage, plumbing or ground-support issues before repairing the visible damage.

Insurance coverage depends on the policy, the cause of the damage and any applicable exclusions. Policies may treat gradual ground movement differently from damage linked to a defined insured event.

Review your Product Disclosure Statement and contact your insurer before beginning non-emergency repairs. Your insurer may require photographs, an assessment or an engineer’s report before deciding whether the damage is covered.

You can contact a subsidence repair specialist for an initial site assessment. This can help identify the visible signs of movement, likely contributing conditions and possible treatment requirements.

A structural or civil engineer may also be required where the movement is substantial, the damage is complex, the cause is uncertain or formal engineering documentation is needed. Your insurer may have its own assessment requirements.

A properly designed foundation repair is intended to provide long-term support, but contributing conditions must also be addressed.

Leaks, blocked downpipes, poor drainage, erosion and significant changes in soil moisture can continue to affect the ground around a home. The repair plan should therefore consider both the affected foundations and the underlying cause of the movement.

Homeowners can help reduce the risk of foundation movement by:

• Repairing leaking pipes, taps, gutters and downpipes promptly
• Keeping stormwater systems clear and functioning
• Directing surface water away from the house
• Avoiding excessive watering beside foundations
• Managing trees and large shrubs near the home
• Avoiding excavation close to footings without professional advice
• Monitoring cracks, uneven floors and sticking doors for change

These steps cannot prevent every ground problem, but they can help reduce large moisture variations and other conditions that contribute to foundation movement.