Foundation Repair Methods: Costs and Benefits

Foundation repair methods fall into a few groups: fixing the cause, filling voids, strengthening the ground, lifting a sunken slab, underpinning the footings and, in the worst cases, replacing them. Each has a different cost basis, a different level of disruption and clear limits. This guide compares them side by side so you can read a report or quote and ask the right questions.

What are the main foundation repair methods?

The main foundation repair methods are leak and drainage repairs, void filling, resin injection, permeation grouting, slab jacking, underpinning and slab or footing replacement. They do different jobs. Some fix the cause, some restore support under the house, and some lift it back towards level. Most repairs combine two or more.

It helps to think of them by what they fix:

• The cause. Leak repairs and drainage stop the water that moves the soil.
• The ground. Void filling, resin injection and grouting fill gaps and strengthen weak soil.
• The level. Slab jacking and resin lifting raise a sunken slab or footing.
• The support. Underpinning and screw piles carry the load down to firmer ground.
• The structure itself. Replacement is for concrete that is too damaged to save.

Before any of these, someone needs to work out what is moving the house. Our guide to diagnosing an unlevel building explains the tests. If you are not sure the problem is in the foundation, start with is it just a crack or a structural issue?

Step one: fix the cause

Every lasting foundation repair starts by fixing what moved the soil. In Australian homes, the most common issues are water: leaking pipes, broken stormwater drains, downpipes discharging at the footings or poor site drainage. Trees and poorly compacted fill are the other usual causes. Repairs that skip this step can fail.

CSIRO’s homeowner guide to foundation maintenance and footing performance explains how moisture changes in clay make footings move. Our guide to reactive clay and moisture covers this in plain terms.

• Benefits: often the cheapest part of the job, and it protects every subsequent repair.
• Limits: it stops further movement but does not reverse movement that has already happened.
• Cost basis: plumber or drainage contractor rates and the length of pipe or drain involved.

Our water leak management service finds and fixes leaks linked to ground movement.

Void filling and ground improvement

Void filling and ground improvement restore support by filling gaps and strengthening weak soil under a slab or footing. They suit homes where soil has washed out, been poorly compacted or softened, but the footing itself is sound and firm ground is not far down. Work is done through small holes, so disruption is low.

Void filling fills empty spaces beneath slabs, often after a leak has washed away soil.

Resin injection pumps expand polyurethane resin into the ground under the footing. The resin fills voids, compacts loose soil, and can lift the structure in controlled steps. Our comparison of underpinning and resin injection explains where it fits.

Specialised grouting uses permeation grouting, in which fine cement grout binds sandy soil. It can suit beachside and sandy sites.

• Benefits: little or no excavation, fast, and most homes stay lived in during the work.
• Limits: not suitable when the load must reach much deeper ground, and not all soils accept resin or grout.
• Cost basis: treatment area, volume of resin or grout, number of injection points and any lift needed.

Lifting a sunken slab

Slab jacking lifts a sunken concrete slab back towards level by injecting material underneath it through small holes. It suits floors, paths, driveways and garage slabs that have dropped because the soil below has settled or washed out. It restores the level, but on its own, it does not deepen support.

Read more on our slab jacking page and in our concrete levelling guide. For a direct comparison, see slab jacking or underpinning: which one does your home need?

• Benefits: much less disruption than replacing a slab, and the existing concrete is kept.
• Limits: the slab must be in reasonable condition, and lifting will not hold if the soil continues to move.
• Cost basis: slab area, lift amount, and number of injection points.

Underpinning: support at a deeper level

Underpinning strengthens or deepens existing footings so they carry the house load down to firmer ground. Methods include mass-concrete pins driven under the footing, screw piles, bored piers, and mini-piles. A structural engineer designs the work. Underpinning suits homes where the existing footing is too shallow or the upper soil is too weak.

Our guide to which underpinning method to use compares each method in detail and explains what happens during house underpinning, walking through the process on site.

• Benefits: a long-term structural fix that reaches below the problem soil.
• Limits: more excavation, time and cost than ground improvement. It still needs the cause fixed on reactive clay.
• Cost basis: number and depth of pins, piers or piles, site access, engineering and reinstatement.

See our underpinning service, or our local teams for underpinning in Melbourne and Brisbane.

Replacing the slab or footing

Replacement means breaking out damaged concrete and pouring new slabs or footings. It is the most disruptive and usually the most expensive foundation repair. It is generally reserved for concrete that is badly broken, structurally unsound, or too damaged for lifting or underpinning to be effective. An engineer should first confirm that the repair is not practical.

• Benefits: a new slab or footing designed for the site as it is now.
• Limits: high disruption, often requiring the house or part of it to be vacated, plus demolition, waste removal and new finishes.
• Cost basis: area, demolition, engineering, new concrete and reinforcement, and replacing floor coverings.

A note on stumps: homes on timber or concrete stumps may need restumping, which is a different level. Raise & Relevel does not do restumping. If stumps are the problem, we will tell you.

Foundation repair methods compared

How much does foundation repair cost?

Foundation repair costs depend on the method, the size of the affected area, the depth to firm ground, site access, and the extent of the house’s movement. Each method is priced differently, so a reliable price can only be determined after an inspection and a structural engineer’s assessment. Fixing the cause is usually the smallest cost.

The one figure we publish is for underpinning. On our Melbourne underpinning page, we state that most underpinning costs fall between $5,000 and $30,000. Minor work generally costs $5,000 to $10,000, and moderate work costs $10,000 to $30,000 or more. Other methods are quoted after a site inspection.

What moves the price for any method:

• The cause of movement and the cost of fixing it.
• The area to be treated, lifted or supported.
• The depth to firm, load-bearing ground.
• Site access for equipment.
• The soil type, including reactive clay or sand.
• Engineering reports, certification and monitoring.
• Making good: patching cracks, re-hanging doors, replacing floor coverings.

When you compare quotes, check that each one applies to the same engineering scope and states whether GST, engineering, waste removal, and making good are included. Online national averages have not seen your site, so treat them with care. Home insurance may cover damage from a sudden insured event, such as a burst pipe, but often excludes gradual movement. Moneysmart explains how to choose home insurance.

When is each method the wrong choice?

Each foundation repair method has clear limits. The wrong method costs money and may not last. The most common mistakes are lifting a slab without fixing a leak, using ground improvement where the load needs deeper support, and replacing concrete that could have been lifted or supported.

• Resin injection or void filling is the wrong choice when firm ground sits well below the footing, and the house needs deeper support.
• Slab jacking is the wrong choice when the slab is severely cracked or broken, or when the soil beneath is still moving.
• Underpinning may be more than you need when the problem is a void or soft soil near the surface.
• Replacement is often more than you need when the concrete is sound and only out of level.
• Any method is the wrong choice if the leak, drain or tree causing the movement is left in place.

How do you choose a foundation repair contractor?

Choose a foundation repair contractor who diagnoses the cause before recommending a method, works to the engineer’s design for structural work and holds the right licence for your state. A good contractor will also say when a method they offer is not the right fit for your home.

• Diagnosis. Ask for a written explanation of the cause, not only the symptom.
• Engineering. For structural repairs, ask who the engineer is. You can check engineers on the National Engineering Register.
• Soil class. Ask how the site’s soil classification under AS 2870 for residential slabs and footings affects the method.
• Licence. In NSW, a contractor licence is required for residential building work over $ 5,000, including GST. Check licences on the NSW Government licence check, BPC in Victoria, QBCC in Queensland or Access Canberra.
• Warranty. Ask what is covered, for how long and what voids it.

Our licence numbers are NSW 377694C, VIC CDB-U 73507, QLD 15300551 and ACT 20211579.

Frequently asked questions

What is the most common foundation repair method?

There is no single most common method for every home. For Australian houses on clay, the work often combines fixing leaks or drainage with ground improvement, such as resin injection, or with underpinning. The right mix depends on the cause, the soil and how far the house has moved.

What is the cheapest foundation repair method?

Fixing the cause, such as a leaking pipe or poor drainage, is usually the cheapest step and should come first. Among structural methods, ground improvement and slab jacking usually cost less than underpinning because there is little excavation. They only work if they suit the problem, so compare methods against the same engineering scope.

How long does foundation repair take?

It depends on the method and the size of the job. Void filling, resin injection,n and slab jacking are often completed within days because they require no excavation. Underpinning takes longer, as concrete pins are dug and cured in stages. Replacement takes the longest. Your contractor should give you a timeline with the quote.

Is foundation repair permanent?

Foundation repair is long-term when the cause is fixed, and the method suits the soil and the load. Repairs can fail when a leak keeps running, drainage stays, or the method was wrong for the ground. Ask your contractor what the warranty covers and what maintenance is expected of you.

Does home insurance cover foundation repair?

Sometimes. Many policies cover damage from a sudden insured event, such as a burst pipe, but exclude damage from gradual ground movement or poor maintenance. Your product disclosure statement decides it. Check with your insurer before work starts if you think you have a claim.

Find the right repair for your foun.dation

Foundation repair methods range from simple leak repairs to full replacement, and the best result usually comes from fixing the cause first, then using the least disruptive method that will last. Compare methods by what they fix, how they are priced and where they fall short, not just by price.

If you have noticed cracks, sinking floors, or signs of subsidence, our team can inspect your property, identify the cause,e and explain which repairs suit your foundation, including when another trade is the better fit.

Book a foundation inspection or call 1300 053 835.