Underpinning can save your home by giving a moving or failing foundation new support, so the cracks, sloping floors and sticking doors stop getting worse. It works by transferring the building’s weight to stronger ground. It is the right fix when the footing itself can no longer carry the house, and the wrong one when a smaller repair would solve the cause.
This guide explains what underpinning protects, the signs that point to it, how the main methods work, which method suits which home, and when you do not need it at all.
How Does Underpinning Save a Home?
Underpinning saves a home by stopping foundation movement at its source. New support is built under or beside the existing footing and carried down to ground capable of bearing the load. Once the house is supported, damage from movement, such as widening cracks and distorted frames, stops spreading.
Underpinning is the process of strengthening or extending the support beneath an existing building. That support can be a deeper, more concrete footing, a steel pier driven into firmer ground, or treated ground beneath the footing. Whichever method is used, the goal is the same: the house stops moving.
That protection matters for three reasons:
- Structural safety. Active movement can distort door and window frames, crack walls and, in severe cases, cause walls to lean or bulge.
- Repair costs. Movement left unchecked tends to spread. A problem in one corner can grow to involve a whole wall.
- Selling or insuring. An explained, repaired and documented foundation problem is easier for buyers and insurers to accept than an unexplained one.
One point to be clear on: underpinning stabilises a house, but it does not always lift it back to level. Re-levelling is a separate goal, and it should be written into the scope if you want it. Our guide to how house levelling works explains the difference.
Why Do House Foundations Need Underpinning?
Foundations need underpinning when the footing, or the ground under it, can no longer carry the house reliably. The most common causes in Australian homes are reactive soil, water leaks, ageing footings, extra building load and subsidence.
- Soil movement. Reactive clay swells when wet and shrinks when dry. CSIRO’s homeowner guide, Foundation Maintenance and Footing Performance, explains that “all clays react to the presence of water by slowly absorbing it, making the soil increase in volume.” Nearby trees contribute to it because their roots draw moisture from the soil beneath the footing. Read more on reactive clay and moisture movement.
- Water leaks and erosion. CSIRO notes that “even a minuscule leak can be enough to saturate a clay foundation.” Leaking pipes, broken stormwater lines and poor drainage can soften or wash away the soil beneath a footing. See how water leaks cause subsidence.
- Ageing footings. Older homes were often built on shallower footings than current standards require, and materials deteriorate over time.
- Structural changes. An extension or a second storey adds weight to the original footing, which was never designed to carry.
- Subsidence. The ground beneath part of the house sinks, compresses, or erodes, leaving the footing unsupported.
Signs Your Home May Need Underpinning
A home may need underpinning when several signs of movement appear together and continue to worsen. Look for:
- Cracks that widen or come back after repair, especially stepped cracks in brickwork or cracks running from the corners of doors and windows
- Sloping, sagging or uneven floors
- Doors and windows that stick or no longer latch
- Gaps opening between walls, floors and ceilings, or at skirting boards and cornices
- Part of the house is visibly leaning or sinking
These signs do not prove that underpinning is needed. Some cracks are cosmetic, and others are due to small-scale issues that a small pair can fix. Our guide to distinguishing a cosmetic crack from a structural issue helps you assess what you are seeing. If part of the house is leaning, get a structural assessment promptly.
Underpinning Methods Explained
The three methods most commonly used on Australian homes are mass concrete underpinning, screw piles or piers, and resin injection. They differ in how they support the house, how disruptive they are and what ground conditions they suit.
Mass Concrete Underpinning
Mass concrete underpinning, sometimes called traditional or pit underpinning, extends the existing footing downwards. Sections under the footing are excavated one at a time and filled with concrete, so the house is never left unsupported. It is a long-established method using conventional materials. The trade-offs are excavation, curing time and the need for good access around the house.
Screw Piles and Piers
Screw piles are steel shafts with helical blades that are driven into the ground beside or under the footing until they reach soil capable of carrying the load. Bored piers serve a function similar to that of drilled concrete columns. Piers suit sites where suitable bearing ground is deep. They need machine access, and steel piles need protection against corrosion.
Resin Injection
Resin injection uses expanding polyurethane resin injected through small drilled holes into the ground under the footing. The resin fills voids and compacts weak soil, which can stabilise the footing and, in suitable cases, lift it back towards level. It is far less disruptive than excavation. It is not suitable for every soil type or every structural problem, and an assessment should confirm it fits the cause. Read more about resin injection.
For a detailed comparison, including how soil, load and access narrow the choice, see which underpinning method suits a given project.
Which Underpinning Method Suits Your Home?
The right method depends on what is causing the movement, the soil, how deep firm ground is and how easy the site is to access. The table summarises where each method tends to fit. An on-site assessment makes the final call.
| Method | Usually suits | Main limitations | Disruption |
| Resin injection | Voids, loose fill or soft soil under a slab or strip footing; homes where excavation is hard | Not for every soil type or a footing that was always inadequate | Low: small holes, often completed quickly |
| Mass concrete underpinning | Shallow footings where firm ground is reachable at moderate depth | Excavation, curing time, and access around walls | High |
| Screw piles or bored piers | Deep soft soil, where firm ground is well below the footing | Machine access; corrosion protection for steel | Low to medium |
We carry out resin injection, mass concrete underpinning, and screw piling, so the recommendation follows the diagnosis rather than a single preferred method. We do not do restumping. If your timber-floored house needs new stumps rather than new footings, we will tell you.
Local ground conditions matter too. The QBCC notes that most Queensland homes sit on clay soils that dry out and wet up quickly with the seasons, and soils vary just as much across Melbourne and Sydney. See our pages on underpinning in Melbourne and underpinning in Brisbane for local detail, or our underpinning service for Sydney and nationwide work.
When Underpinning Is Not the Answer
Underpinning is not needed when the movement has stopped, the cracks are cosmetic, or a smaller repair removes the cause. Fixing the cause first can save thousands.
Underpinning may not be the right repair when:
- Cracks have stayed the same size over months of monitoring
- A leaking pipe or poor stormwater drainage is the main cause and can be repaired
- A slab has dropped, but the footing is sound, so slab lifting or re-levelling will do
- Stumps under a timber floor, not the footing, are the problem
- A retaining wall, not the house footing, is moving
Fixing a leak or drainage problem removes the cause, but it does not undo damage already done. Whether the house still needs support is a question for the assessment. Our comparison of underpinning, re-levelling and slab lifting sets out which fix fits which problem.
What Affects the Cost of Underpinning?
Underpinning cost depends on the method, the number of supports, how deep they must go, soil conditions, site access and how much reinstatement is needed afterwards. In Melbourne, most residential underpinning costs between $5,000 and $30,000, with larger structural jobs costing more.
The main cost drivers are:
- Extent of damage: how many footing points and how much of the wall needs support
- Method and depth: resin quantity, number and depth of piers, or volume of concrete
- Site conditions: soil, groundwater, slope and access for excavation or machinery
- Engineering and approvals: reports, design and any council requirements
- Reinstatement: paving, landscaping, drainage and cosmetic repairs inside
Ask every quote to state whether it is priced per pier, per metre, or per project, and whether GST, engineering, re-levelling, and cosmetic repairs are included. See our guide to underpinning methods and cost factors.
Choosing an Underpinning Contractor
Choose a licensed contractor who inspects the house, identifies the cause, and recommends a method or provides a price before proceeding. A quote based only on photos or the width of a crack is a guess.
Check the licence with the regulator in your state, not the logo on the quote. In New South Wales, underpinning and piering is a licensed category of work, and a contractor licence is required for residential building work valued at more than $5,000, including labour and materials. Other states run their own schemes.
| Where your property is | Check a licence |
| New South Wales | Categories of licensed building and trade work |
| Victoria | Building and Plumbing Commission: find and check a practitioner |
| Queensland | QBCC registers, including the licensee register |
| ACT | Access Canberra building and construction registers |
If an engineer is involved, you can search the Engineers Australia’s National Engineering Register. We have re-levelled more than 7,000 homes, and our licence numbers are NSW 377694C, VIC CDB-U 73507, QLD 15300551 and ACT 20211579.
Frequently Asked Questions
How long does underpinning last?
Properly designed and installed underpinning is intended to give long-term support. How long it performs depends on the diagnosis, the design, the ground and how the site is maintained, especially drainage. No contractor should promise that future movement is impossible. Ask what the product and artistry warranties cover and how long each runs.
Can you live in your house during underpinning?
Often, yes. Many homes stay occupied during resin injection and smaller jobs. Larger excavation work may temporarily affect access to water, power, or gas, and some projects may require temporary relocation. Your contractor should confirm in writing which parts of the house will be off limits and for how long.
Does underpinning devalue a house?
Not usually. Underpinning fixes a structural concern that would otherwise worry buyers, and documented repairs give a purchaser something concrete to rely on. Value still depends on the property and the market. Keep every engineering report, invoice, warranty and completion document. Our guide to buying or selling a house with subsidence covers this in more depth.
Does home insurance cover underpinning?
Sometimes. Insurance may respond to foundation damage caused by a sudden insured event, while damage that develops gradually is treated differently by most policies. Your product disclosure statement decides it. ASIC’s Moneysmart guidance on choosing home insurance explains how to check exclusions. Talk to your insurer before starting non-emergency work.
Does a crack in my home mean I need underpinning?
No. Most fine cracks are cosmetic and need only filling and painting. Cracks that widen, return after repair or appear with sticking doors and sloping floors are more concerning. Those movement points should be assessed before any repair. See what it costs to fix cracks in a wall for both kinds.
The Bottom Line
Underpinning can save your home when the footing or the ground beneath it can no longer carry the house. It stops movement at the source, protects the structure and makes repairs last. It is not the answer for every crack. The right first step is an assessment that finds the cause, then a method matched to your house and soil.
Book an Underpinning Assessment
Seeing cracks, sloping floors or doors that stick? We find out what is moving your home, explain whether underpinning is needed, and provide a written quote that spells out what is included. See our underpinning service, or book an assessment with our team in Sydney, Melbourne or Brisbane. Call 1300 053 835.
