Underpinning strengthens or deepens a building’s footings so it stops moving. As of October 2026 there is no independent Sydney price survey. Resin-injection contractor Mainmark publishes mass concrete underpinning at about $1,000 to $3,000 per metre and mini-piles at $10,000 to $20,000 per pile, with jobs often $5,000 to $50,000 or more. Get a structural engineer’s report before any quote.
- Underpinning is a structural repair to footings. A structural engineer should diagnose the cause and specify the method first.
- Mainmark publishes mass concrete underpinning at $1,000 to $3,000 per metre and beam and base at $1,500 to $3,500 per metre.
- Mini-piled underpinning costs $10,000 to $20,000 per pile depending on depth, according to Mainmark.
- Clay soils in much of Western Sydney and the Hills shrink and swell with moisture, which can move footings.
- Fixing leaks, drainage and tree problems is often part of the cure, with or without underpinning.
What is underpinning?
Underpinning is a structural repair that strengthens, deepens or widens a building’s footings so they rest on firmer ground. It is used when footings have sunk, moved or no longer carry the house properly.
It is a specialist job. The right method depends on the soil, the house and the cause of the movement. That is why a structural engineer, not the contractor selling the repair, should decide what is needed.
What are the signs your house needs underpinning?
Cracks alone do not prove you need underpinning. Many cracks are cosmetic, and some come from leaks or seasonal soil movement that can be fixed in other ways. Look for patterns, and call a structural engineer if you see several of these signs.
| Sign | What it can mean | Next step |
|---|---|---|
| Stepped cracks in brickwork | Part of the footing may be moving | Note the width and length, photograph and date them |
| Diagonal cracks from door or window corners | Uneven movement under the wall | Check whether they open and close with the seasons |
| Doors and windows that stick or will not latch | Frames pushed out of square | Rule out swelling timber or worn hinges first |
| Sloping or bouncy floors | Settled footings, piers or rotten bearers | Have the subfloor inspected |
| Gaps between skirting and floor, or walls and ceiling | The structure has moved | Measure and monitor over time |
| Cracks that keep getting wider | Ongoing movement | Get a structural engineer’s inspection promptly |
General guidance only. A structural engineer should assess any cracking that is wide, growing or affecting doors and windows.
Why do Sydney homes move?
Most footing movement comes from changes in soil moisture. Clay soils swell when wet and shrink when dry. Much of Western Sydney and parts of the Hills District sit on clay soils formed over shale, and many lots there are classed as reactive under AS 2870, the Australian Standard for residential slabs and footings.
Common triggers include:
- Leaking water pipes, sewer lines or stormwater drains that soak the soil under one part of the house.
- Poor drainage, such as downpipes that empty against walls or paving that slopes towards the house.
- Large trees close to the house, which can dry out clay soil in summer.
- Long dry spells followed by heavy rain, which can make cracks open and close.
- Original footings that were too shallow or built on poorly compacted fill.
Changing drainage on clay can itself cause cracking. The NSW Heritage Office warns that rearranging site drainage on reactive clay may upset the existing balance, and suggests geotechnical advice where clay soils are a problem.
Why should you get an engineer’s report first?
An engineer’s report tells you what is moving, why, and what will fix it. Without it, you could pay for underpinning that does not solve the problem, or miss a cheaper fix such as repairing a leaking drain.
- Photograph cracks with a ruler in shot, and date each photo.
- Check for obvious water sources: leaking taps, blocked gutters, downpipes and drains.
- Engage an independent structural engineer to inspect and, if needed, order a soil test.
- Get a written report with the cause, the repair method and any drawings.
- Ask your engineer or a certifier whether the work needs approval.
- Get quotes from licensed contractors based on the engineer’s design, not their own diagnosis.
Structural movement can get worse over time. If a crack is widening quickly, doors suddenly jam, or you see bulging walls or sagging ceilings, keep people clear of the area and get a structural engineer out promptly.
What are the main underpinning methods?
There are several ways to underpin a house. The table compares the methods described in Mainmark’s underpinning guide. Mainmark sells resin injection, so treat its cost comments as a contractor’s view.
| Method | How it works | Often suited to | Published price |
|---|---|---|---|
| Mass concrete | Sections under the footing are dug out in stages and filled with concrete | Shallow footings, where firm ground is not too deep | $1,000 to $3,000 per metre (Mainmark) |
| Beam and base | A reinforced concrete beam spreads the load to concrete bases below | Heavier walls or where loads need spreading | $1,500 to $3,500 per metre (Mainmark) |
| Mini-piles | Small-diameter piles of 150–300 mm carry the load to deeper, stable ground | Deep soft soil or limited access | $10,000 to $20,000 per pile, by depth (Mainmark) |
| Screw piles (helical piers) | Steel screw piles are wound into the ground without major excavation | Light structures, piers and limited digging | No reliable published price found |
| Resin injection | Expanding resin is injected through small holes under the footing to fill voids and lift | Lower-impact repairs where the engineer agrees it suits the soil | No per-unit price published; Mainmark says it is generally cheaper than traditional methods |
Source: Mainmark guide to underpinning (2026). Prices are indicative and exclude engineering, approvals and making good.
Mainmark says resin cures in about 30 minutes and the building can be used during the work, while concrete takes several days to reach strength. Your engineer will choose a method based on your soil test, not the speed of the job.
How much does underpinning cost in Sydney?
As of October 2026, there is no independent Sydney cost survey for underpinning. Mainmark’s cost guide says Australian underpinning jobs often range between $5,000 and $50,000 or more. The per-metre and per-pile rates in the table above come from the same company.
What moves the price:
- How much of the house needs support, measured in lineal metres of wall or number of piers or piles.
- How deep firm ground is, which is found by a soil test.
- Access: tight side passages, subfloors and internal walls take longer.
- Making good: patching cracks, re-hanging doors, repairing paving and painting.
- Engineering, soil testing, certification and any approval fees.
Ask every contractor to price the same engineer’s design, and to list each of these items.
Who does what on an underpinning job?
Underpinning usually involves several people. Knowing who does what helps you avoid paying for the wrong advice.
- Structural engineer: inspects the house, works out the cause of movement, specifies the repair and may inspect the work as it goes.
- Geotechnical engineer or soil tester: drills or samples the ground to find the soil type and how deep firm ground sits.
- Plumber or drainer: finds and repairs leaking water, sewer or stormwater pipes that may be wetting the soil.
- Underpinning contractor: carries out the repair to the engineer’s design.
- Certifier or council: confirms whether approval is needed and, if so, signs off the work.
Keep the engineer’s report, soil test, approvals and the engineer’s final sign-off with your property records. Buyers and insurers may ask for them.
Questions to ask an underpinning contractor
- What is your contractor licence number, and which business name will be on the contract?
- Will you build exactly to the engineer’s design, and who inspects the work?
- How many piers, piles or metres of wall are included in the price?
- What happens if firm ground is deeper than expected?
- Is making good included, such as crack repair, paving and painting?
- What warranty do you give, and if the job is over $20,000, will you provide the Home Building Compensation certificate before taking any payment?
NSW rules for underpinning work
Underpinning is residential building work, so NSW consumer protections apply.
Licence check: look up every contractor on the NSW Government’s free licence check (verify.licence.nsw.gov.au). Make sure the name and licence class match the business on your quote.
Written contract: residential building work worth more than $5,000 including GST needs a written contract. Jobs over $20,000 need a more detailed contract, and you get a cooling-off period of five clear business days.
Deposit: the most you can be asked to pay as a deposit is 10 per cent of the contract price.
Home Building Compensation insurance: for residential building work worth more than $20,000, the contractor must take out this cover before asking you for any deposit or payment. Ask for the certificate.
Warranties: NSW law gives you statutory warranties on home building work: 6 years for major defects and 2 years for other defects.
Get underpinning quotes from our crew
Once you have an engineer’s report, describe the job to MyTradeCrew and mention the method it recommends. We will send it to up to three vetted local trades from our crew, who can price the engineer’s design and contract with you directly.
Frequently asked questions
What is underpinning a house?
Underpinning a house means strengthening or deepening its footings so they sit on firmer ground and stop moving. Methods include mass concrete, beam and base, piles and resin injection. A structural engineer chooses the method after finding the cause of the movement and testing the soil.
Is resin injection underpinning cheaper?
Mainmark, which sells resin injection, says it is generally cheaper than traditional methods and can be done while you use the building. It does not suit every site. Ask an independent structural engineer whether resin suits your soil and the cause of the movement before choosing it.
How long does underpinning take?
It depends on the method and size of the job. Mainmark says resin cures in about 30 minutes, while concrete underpinning takes several days to reach strength and is usually done in stages. Your contractor should give you a written timeline based on the engineer’s design.
Are cracks in my walls a sign of subsidence?
Not always. Hairline cracks are often cosmetic, and some open and close with the seasons on clay soils. Cracks that are wide, stepped, growing, or paired with sticking doors and sloping floors need a structural engineer’s inspection to find the cause.
Does home insurance cover underpinning?
It depends on your policy and the cause of the movement. Read your policy wording and ask your insurer before work starts. An engineer’s report on the cause will help with any claim, so get one before you commit to repairs.
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