What Is the Best Way to Fix a Sinking House in Australia?

The right repair method depends on the cause of the problem, the soil conditions, the foundation type, the severity of the movement and whether the movement is still progressing.

For some homes, the solution may involve improving weak ground, filling voids or re-levelling affected areas. For others, traditional underpinning or structural support solutions may be required.

Mainmark helps Australian homeowners assess foundation movement and provide site-specific solutions, including non-invasive resin injection, ground improvement and house re-levelling options that may reduce the need for disruptive excavation, depending on the property.

The best way to fix a sinking house in Australia is to address the underlying ground or foundation issue before repairing visible damage such as wall cracks, brick cracks or uneven floors.

In simple terms, the process should be:

1. Identify the signs of movement
2. Understand what is causing the sinking or settlement
3. Assess the soil, foundation type and extent of movement
4. Choose the most suitable repair method
5. Re-level, re-support or improve the ground where required
6. Complete cosmetic repairs only after the underlying issue has been addressed

So, is there one best repair method for every sinking house? No. A sinking slab, subsiding brick veneer home, double brick house with stair-step cracks, or home affected by poor drainage may each require a different approach. That is why a site assessment is so important.

Australian homes can be affected by a wide range of ground and foundation conditions. In many areas, particularly where reactive clay soils are present, the ground can shrink and swell as moisture levels change. During dry periods or drought, clay soils may shrink as they lose moisture. After heavy rain, poor drainage or plumbing leaks, the same soils may swell or soften. This movement can create uneven support beneath footings, slabs and foundations.

Common causes of a sinking house include:

• Reactive clay soils expanding and shrinking with moisture changes
• Drought followed by heavy rainfall
• Poor site drainage or blocked stormwater systems
• Leaking pipes or broken sewer lines
• Erosion or soil washout beneath footings
• Poorly compacted fill beneath a slab
• Voids forming under concrete
• Tree roots drawing moisture from the ground
• Natural settlement after construction
• Sloping sites or variable ground conditions

If one part of the house moves more than another, this is known as differential movement. This can place stress on walls, floors, windows, doors and brickwork.

Could poor drainage be making my house sink?

Yes. Poor drainage is a common contributor to foundation movement. Water pooling near the home, overflowing gutters, leaking downpipes or inadequate stormwater control can change the moisture levels in the soil around the foundations. Over time, this can weaken ground support, contribute to voids, or increase movement in reactive soils.

Not every crack means your house is sinking. Some cracks are cosmetic and may be caused by normal building movement, material shrinkage or minor settlement. However, multiple symptoms appearing together can suggest a deeper issue.

Common signs of a sinking house or foundation settlement include:

• Cracks in walls, especially diagonal cracks
• Cracks in brick walls or stair-step cracks in brickwork
• Cracks around windows and doors
• Sticking doors or doors that no longer latch properly
• Windows that jam or distort
• Uneven floors or sloping floors
• Gaps between walls, floors, ceilings or skirting boards
• Sinking slabs, patios, driveways or garage floors
• Floors that feel bouncy, hollow or unsupported
• New cracks that continue to widen over time

They can be. Cracks in brick walls may be caused by foundation settlement, house subsidence, moisture changes in reactive soils, lintel issues, thermal movement or other building-related factors.Stair-step cracks, diagonal cracks from window or door corners, or cracks that appear alongside uneven floors and sticking doors should be assessed by an experienced professional.

There are several ways to repair a sinking house in Australia. The right option depends on what has caused the movement and what needs to be re-supported.

1. Traditional Underpinning

Traditional underpinning usually involves excavating beneath existing footings and installing new concrete support. It can be suitable for some homes where deeper structural support is required.

However, it may involve significant excavation, access limitations, longer project timeframes and disruption around the home. It may also require careful engineering input, depending on the property and site conditions.

Best suited for:
Homes requiring deeper foundation support or engineered structural intervention.

Considerations:
Can be more disruptive, may involve excavation and may not be necessary for every sinking house.

Learn more about Resin Injection 

2. Resin Injection Foundation Repair

Resin injection foundation repair involves injecting an engineered expanding resin into targeted areas beneath the home, slab or footing. As the resin expands, it can help fill voids, improve ground support and, in some cases, lift and re-level affected areas.

For many Australian homeowners, resin injection may offer a non-invasive alternative to traditional underpinning, depending on the cause and severity of the movement.

Mainmark’s Teretek® resin injection technology is designed to address subsided structures, improve ground and fill voids. It can be used for ground improvement, house re-levelling, void filling and slab lifting where site conditions are suitable.

Best suited for:
Sinking slabs, uneven floors, voids beneath footings, foundation settlement and some forms of house subsidence.

Considerations:
Requires proper assessment to confirm suitability and injection design.

3. Ground Improvement

Ground improvement focuses on improving the ground beneath a structure so it can better support the home. This may involve increasing soil bearing capacity, filling voids, reducing looseness or improving support beneath existing foundations.

This is important because a sinking house is often not just a “building problem”. It may be a ground problem.

Best suited for:
Weak ground, loose soils, voids, settlement and areas where foundation support has been reduced.

Considerations:
The method must match the soil type, structure and movement pattern.

Learn more about Ground Improvement 

4. House Re-Levelling

House re-levelling is used when part of a home has dropped, settled or moved out of level. Depending on the site, resin injection or other ground engineering methods may be used to gently raise and re-support affected areas.

This can help address symptoms such as uneven floors, sinking foundations, cracks in walls and sticking doors when these are caused by ground or foundation movement.

Best suited for:
Homes affected by differential settlement or localised sinking.

Considerations:
Re-levelling should be controlled and based on what the structure can safely tolerate.

Learn more about house Re-levelling

If you patch cracks, repaint walls or replace cracked tiles before addressing the cause of movement, the damage may return.Cosmetic repairs can improve the appearance of your home, but they do not solve sinking foundations, weak ground, voids, poor drainage or foundation settlement.

For example:

• Patching cracks will not fill voids beneath a slab
• Repainting walls will not stop ongoing soil movement
• Replacing cracked tiles will not re-support a sinking floor
• Trimming sticking doors will not correct a distorted frame
• Repointing cracked brickwork will not fix foundation settlement

That is why the best repair sequence is usually: assess first, treat the underlying cause, then complete cosmetic repairs.

Should I fix the cracks before repairing the foundation?

In most cases, it is better to understand and address the cause of the cracks first. If the home is still moving, cosmetic repairs may crack again.

You should arrange an expert assessment if you notice more than one sign of movement, if cracks are widening, or if doors, windows and floors are changing over time.

It is especially worth getting your home assessed if you notice:

• New or growing cracks in walls
• Cracks in exterior brick walls
• Stair-step cracks in brickwork
• Uneven or sloping floors
• Sticking doors and cracks in walls together
• Gaps around windows or door frames
• Sinking concrete slabs around the home
• Cracks returning after previous repairs
• Movement after drought, heavy rain or drainage issues

A professional assessment can help determine whether the issue is cosmetic, seasonal, related to building materials, or linked to foundation movement or house subsidence.

If you are worried about a sinking house, avoid jumping straight into cosmetic repairs without understanding the cause.

Try not to:

• Patch every crack without monitoring movement
• Trim doors just so they close again
• Ignore drainage issues around the home
• Assume all cracks are harmless
• Assume all cracks are serious
• Replace flooring before checking whether the slab is sinking
• Delay assessment if symptoms are getting worse
• Choose a repair method before the cause is understood

A calm, practical approach is best. Take photos, note when symptoms appeared, check drainage and arrange an assessment if the signs suggest possible movement.

Mainmark has provided ground engineering and foundation repair solutions since 1989, helping Australian homeowners address issues caused by ground movement, subsidence, weak or reactive soils, voids and foundation settlement.

Mainmark’s approach is based on understanding the cause of the problem before recommending a repair method. Depending on the site conditions, solutions may include:

• Foundation repair
• House re-levelling
• Ground improvement
• Resin injection
• Void filling
• Slab lifting
• Underpinning alternatives
• Structural support solutions
• Subsidence repair

For suitable homes, Mainmark’s non-invasive resin injection and ground improvement solutions may reduce the need for disruptive excavation or traditional underpinning.

Mainmark can assess your property and help identify whether the issue is cosmetic, seasonal or related to ground movement, voids, weak soils or foundation settlement.

Contact Mainmark to arrange a site assessment and find out which foundation repair, house re-levelling or ground improvement solution may be right for your home.