We’ve created this step-by-step guide to underpinning to help you decide if your house actually needs underpinning — and what the process involves if it does.
Underpinning is the construction of new, deeper footings under an existing house to stabilise it and prevent ongoing or further movement or subsidence. It can involve extra concrete footings or steel screw-in pier footings that support the building on more stable soil, found deeper below the surface.
Finding cracks in your house can be a confusing and scary time, and underpinning might be the answer. This guide is here to help you work out whether it is.
Cracks in Your Home
Finding cracks in your home can be scary.
I know because I hear this all the time.
I have concerns about the structural integrity of my house which may be the result of movement of the concrete slab or footings. I do not know whether I should be talking to a structural engineer or someone specialising in underpinning or slab stabilisation.
Scary stuff, right?
We put so much love into our homes. So much trust. We want our homes to protect us and keep us safe.
So when our houses move and crack, it is only natural to want to stabilise that movement as quickly as possible.
As structural engineers trusted by many to help fix their houses, we have a few tools to help fix your home and stop it moving. In our toolbox, underpinning is the big tool. The game-changer. The winning blow. But it is also expensive, and it can make a mess of your home if done badly.
Depending on your circumstances and why your house is moving, underpinning just might be the perfect tool to fix your home. Or it might not be.
First, let’s get back to basics.
What is Underpinning?
Underpinning a house, a residential dwelling, or even a commercial building is the construction process of strengthening the foundation by building additional concrete or steel footings to stabilise, strengthen, or lift the existing footings.
Underpinning is a construction process that adds extra footings beside and under your house so that it is supported on soil that is more stable than the soil your home currently sits on.
The purpose of underpinning is to support your footings on soil that is more stable, stiffer, stronger, and less likely to move in future.
Google says, “Underpinning is a solid foundation laid below ground level to support or strengthen a building.”
When structural engineers specify underpinning for houses, it is normally to support a house suffering from one-way downward movement of soil, where the existing footings need to be supported on deeper, more stable ground.
In short: an “underpin” is the new footing itself. “Underpinning” is the process of installing it. Both terms describe the same family of work, and you’ll see both used by engineers, builders, and underpinning contractors.
When Does a House Need Underpinning?
Underpinning is such a popular term right now in relation to fixing movement problems in houses. But is underpinning the right solution for your house movement problem?
House footings move for different reasons, and not all footing movement requires underpinning.
So when is underpinning actually needed?
Underpinning is useful when the footings for a house or set of units have subsided or dropped for a reason that is unlikely to reverse.
Examples of footing movement that is unlikely to reverse include a footing constructed on loose or soft soil, such as uncontrolled fill.
If your house footings weren’t originally installed deep enough, underpin footings can be used to improve the stability of your house. They can even be used to jack your house back up to almost level.
When Is Underpinning NOT Recommended?
Footing movement that might reverse is caused by uneven changes in soil moisture content in clayey soils — also known as slab heave. Underpinning is not recommended for solving slab heave.
This movement is caused by an effect that can be reversed. In our opinion, underpinning is not the best way to solve issues with reactive clay movement.
If your cracking is seasonal — opening up in dry weather and closing again after rain — read our guide to What Is Slab Heave before you call an underpinning contractor. Underpinning the wrong problem is an expensive mistake.
How Is Concrete Underpinning Performed?
Concrete underpinning a house normally involves digging new bored pier footings beside the house, at 2m to 3m centres around the outside.
Sometimes concrete underpins are also required inside the house. The underpin footings have to go deep enough to found into soil that is strong enough to support the weight of the building.
Next, the deeper footings have to be joined to the existing building. Often this is achieved by digging under the existing footing — “undermining” the footing — to create a strong prop for it.
Each pier and prop arrangement is then reinforced with steel reinforcement bars and filled with concrete.
Clever underpinning contractors leave enough space between the underpin and the existing footing so that, once the concrete is strong enough, the underpin can be used to jack the house back up and level it.
Sometimes the jacking procedure will close up the settlement cracks that were in a house — but because cracks sometimes dislodge unevenly, they won’t always close up.
Is Underpinning Only Done on Outside Footings?
No. The footings in the middle of a house can be underpinned too. The underpinning contractor has to dig through the slab to access the ground underneath, but the underpinning work then continues as if the footing were on the outside of the house.
How Long Does Underpinning Take?
How long underpinning takes depends on the number of underpins specified by the engineer.
For a house needing up to 10 underpins, the work will typically be done over approximately two weeks.
If your whole house needs underpinning, you might be out of your house for about a month.
How to get your house underpinned in 5 easy steps
Here’s a step by step guide to underpinning:
Step 1: The Structural Engineer’s Assessment
You’ll need a qualified structural engineer to assess your home. The structural engineer should be:
- experienced in assessing and repairing damage
- have local knowledge,
- be registered to practice in your area
- and be easy to speak to.
Arrange for an inspection first — and preferably don’t pre-empt the whole conversation by stating you need underpinning. Leave that assessment to the structural engineer. Describe the symptoms instead: what you’re seeing, when the crack first appeared, that your bedroom door sticks, that there are cracks in the brickwork above the garage.
Some engineers aren’t qualified. Some engineers aren’t independent. It’s a little more work for you, but it reduces the risk of paying for work you don’t actually need. Do your research and make sure you can trust the engineer you engage.
Check whether your engineer is a Registered Professional Engineer of Queensland (RPEQ) on the BPEQ public register.
The Engineer’s Investigation Should Include These Assessments
Your engineer should do these things to investigate house movement and damage — be wary of an investigation that is less thorough than this:
- Inspect and record the damage around your house.
- Inspect around the outside of the house looking for external influencing factors.
- Take floor levels throughout the house to determine which part of the house is moving and work out whether it is lifting or subsiding.
- Ask to see a copy of the original engineering and soil test (if it is available).
- Run a Dial Before You Dig report to see if there are any underground services affecting your property.
- Sometimes, arrange an independent soil test to check the validity of the original soil test.
A decent, experienced engineer’s inspection and report typically costs somewhere between AU$2,500 and AU$3,400. Determining the cause of the movement and cracking is the essential first step before underpinning.
Your house may not even need underpinning. Speak to your engineer about alternatives such as:
- Soil moisture stabilization
- Adjustable stumps
- Flexible joints in walls and ceilings
Want to talk it through first? Send us a message or request a quote.
Step 2: The Soil Test
Your underpinning contractor can’t quote your job until the soil conditions on your site have been assessed.
A soil test is needed to determine how deep the firm soil is — which determines how deep your underpins will need to be.
The soil test for underpinning is not the same as a site classification for building a new home. A soil test for underpinning goes much deeper — typically 6m to 8m — and sometimes also records soil moisture conditions at 500mm depth increments.
Use a soil tester who knows your area and can get a drilling rig into the site.
Step 3: The Engineering Design
This is why you engaged a structural engineer to assess your house in the first place — the engineering design for underpinning should be completed by a registered professional structural engineer local to your area.
The structural engineer uses the information in the soil report to determine the best location, spacing, and depth of underpins needed to stabilise your home.
The engineer didn’t know your house needed underpinning when they first quoted the job, so expect to pay separately for the underpinning design.
Be wary if a salesperson for an underpinning or resin injection company offers to pay for your design — you may end up with more underpins than necessary.
Step 4: Engaging an Underpinning Contractor
Get at least two quotes from underpinning contractors who service your area.
The quotes should explain what’s included, what’s excluded, and a basic indication of what costs could vary. A good underpinning contractor will include prices for removing and replacing concrete slabs, getting plumbing checked after the work is complete, engineer’s inspections during construction, council fees, and workers’ compensation.
If the quotes are hard to compare, ask for references and speak to people who’ve previously used the contractor:
- Did the workers make a mess and refuse to clean it up?
- Were they courteous and friendly?
- Did they do the job they said they would do?
- Were there any unexpected price variations?
Step 5: Construction of the Underpins
The underpinning contractor runs the project from here. They’ll construct the underpins in stages if there are several, and arrange for the structural engineer to attend before each concrete pour to confirm the underpin footings have been excavated to the correct depth.
They’ll place and pour the underpin concrete, then return days later to jack up and stabilise the house.
Your underpinning contractor will finalise the paperwork, give you a copy of the final floor levels, and submit a final invoice.
Does Underpinning Require Building Approval in Queensland?
Yes. If you’re undertaking an underpinning project in Queensland, you’ll need building approval.
To get building approval, you need a set of structural engineer’s drawings. To get a good set of drawings, you need a soil test.
I recommend starting with an engineer’s inspection to determine if underpinning is actually the best way to fix your house. Then, if needed, the structural engineer provides a scope for the soil tester to follow.
Once you have a soil test and engineer’s drawings, you’re ready to speak to underpinning contractors for quotes. The underpinning contractor normally engages the building certifier to arrange building approval.
How to Arrange UnderpinningMost underpinning contractors recommend an inspection and report by a structural engineer first. This matters because it’s important to identify and diagnose footing movement that could reverse with a change in soil moisture conditions — rather than committing to underpinning unnecessarily.
Structural engineers experienced in diagnosing slab heave and slab settlement are the right choice for this investigation. They should recommend independent soil tests before designing a foundation underpin solution, and can specify the depth, diameter, and spacing of the underpins based on construction type, soil strength and type, and the amount of footing movement observed.
Then you’ll need a contractor to arrange building approval and install the underpins. Yes — building approval is required.
Underpinning isn’t technically difficult, but an experienced contractor will have a better feel for managing difficult site conditions and safe house-jacking procedures. The excavations should be inspected by a structural engineer before they’re filled with concrete.Most underpinning contractors recommend an inspection and report by a structural engineer first. This is because it is important to identify and diagnose footing movement that could reverse with a change in soil moisture conditions.
Structural engineers experienced in the diagnosis of slab heave and slab settlement are a suitable choice for this investigation.
The structural engineer should recommend independent soil tests before designing a foundation underpin solution.
The structural engineer can specify the depth, diameter and spacing of the underpins based on the type of construction of the building, the strength of the soil, the type of soil and the amount of footing movement.
Then you’ll need a contractor to arrange building approval and then to install the underpins. (Yes – building approval IS required for the installation of underpinning).
Underpinning isn’t technically difficult but an experienced underpinning contractor will have a better feel for managing difficult site conditions and safe house jacking procedures.
The excavations should be inspected by a structural engineer before they are filled with concrete.
Concrete vs Resin Injection Underpinning
Glad you asked. Resin injection is done by contractors who pump resin into the ground. The resin expands and hardens, and the theory is that your house becomes stable.
But if resin injection doesn’t work and your house keeps moving, unfortunately, we can’t help you. The process can’t be reversed, and it becomes very difficult to stabilise and re-level your house afterwards.
Reputable underpinning contractors know that an investigation into the cause of movement by an experienced, reputable engineer is required before you can properly price an underpinning job.
Beware underpinning and house-raising salespeople who are not engineers and are not registered to provide engineering advice. Their quotes will sometimes include a line like “you should obtain engineering advice before proceeding with this quote” — in Queensland, if they’re giving you engineering advice, they should be a Registered Professional Engineer (RPEQ), or supervised closely by one.
Resin injection is botox for homes — and it’s just as short-term and unqualified, when used without a proper engineering diagnosis first.
Our recommendation: before you engage a contractor to inject resin under your home, make sure a structural engineer — not the contractor’s salesperson — inspects and diagnoses the issue, provides you with a report, arranges a soil test, and confirms in writing that your soil is loose and needs strengthening by resin injection.
If you’ve already had resin injection and your house is still moving, all we can suggest is calling the injection company back to fix it under their warranty scheme. I’m sorry — but at that point, we can’t help.
Underpinning in Queensland
Cornell Engineers has worked with several competent underpinning contractors across Queensland.
We’d be happy to inspect and diagnose your foundation movement, prepare an underpinning specification if relevant and introduce you to an underpinning contractor that suits your project.
Brisbane Underpinning Contractors
We have previously worked with these underpinning contractors in Brisbane. Contact them directly for a quote.
Mehrtens Underpinning and Construction
Frequently Asked Questions
What does underpinning mean? Underpinning means strengthening an existing building’s foundation by constructing new, deeper footings — called underpins — beside or beneath the original footings. The new footings reach down to firmer, more stable soil than the soil the original footings sit on, and they can be used to stabilise a building or jack it back up to a more level position.
What is an underpin? An underpin is the new footing itself — usually a deep pier of reinforced concrete, or sometimes a steel screw pier, installed beside or under an existing footing. “Underpins” is simply the plural: a house might need 10, 20, or more individual underpins depending on the extent of the movement.
Does my house need underpinning, or is it slab heave? Not necessarily. Underpinning is the right tool when footings have subsided due to soft or loose soil and the movement is unlikely to reverse on its own. It is not the right tool for slab heave — seasonal movement caused by reactive clay soils expanding and shrinking with moisture — because that movement can often be managed and stabilised without the cost and disruption of underpinning. An independent structural engineer’s assessment is the only reliable way to tell the difference.
How much does underpinning cost? Costs vary widely depending on the number of underpins required, soil conditions, and access. A structural engineer’s initial inspection and report typically costs between AU$2,500 and AU$3,400. The underpinning construction itself is priced separately by the contractor once a soil test and engineering design are complete — get at least two quotes.
How long does underpinning take? For a house needing up to around 10 underpins, the work is typically completed over about two weeks. If the whole house requires underpinning, you may need to be out of the property for around a month.
Is resin injection the same as underpinning? No. Resin injection involves pumping expanding resin into the ground to try to stabilise it, rather than constructing new physical footings. It can be appropriate in some situations, but it should only be used after a structural engineer — not the contractor’s salesperson — has properly diagnosed the cause of movement. If resin injection fails, the process generally cannot be reversed.
Do I need council or building approval for underpinning in Queensland? Yes. Underpinning works in Queensland require building approval, which means you’ll need a set of structural engineer’s drawings, which in turn requires a soil test. Your underpinning contractor will typically arrange the building certifier once your engineering design is complete.
Can the footings in the middle of my house be underpinned, or only the outside walls? Both. Underpinning can be carried out on internal footings as well as the external perimeter. For internal footings, the contractor needs to dig through the slab to reach the ground beneath, but the underpinning process itself is the same.
Underpinning Your House
Got some problems with your house and think you might need underpinning? We’d love to help.
Send us a message or request a quote and let’s have a chat. I’m sure we can help.
11 replies on “Will Underpinning Save Your Home? What Even Is Underpinning? A Step-by-Step Guide for Homeowners”
Thank you for your introduction. I have read some materials about resin injection, and my level of acceptance is probably quite similar to yours overall.
Generally speaking, I acknowledge that resin injection construction is fast and clean, and it can indeed relevel many footings effectively. However, in my opinion, its primary function is still high-pressure filling, somewhat similar to mudjacking. If the underlying foundation soil later experiences swelling, softening or collapsible settlement due to water ingress or moisture changes, this may eventually lead to a practical failure of the underpinning system. On the other hand, if the soil is reasonably firm during resin injection, the relevelling is carefully controlled, and future moisture variation can be prevented, then the strengthening should perform well, as the mechanical properties of the resin itself should generally be reliable.
By comparison, methods such as reblocking and piling, to varying degrees, usually involve some level of soil replacement and deeper footing embedment into more stable bearing layers. These deeper foundation soils are generally less affected by external temperature changes, surface water or tree root activity, and therefore tend to provide a more stable long-term system. However, these methods are also more expensive and considerably more difficult to carry out in practice.
Great article thank you, anyone in Perth West Australia that you would recommend
I am a contractor in Mechanicsville Va. Thank you for the detailed and very helpful website info.
Hi, thanks for “What is underpinning”, which gives me related in-depth knowledge. But I have a question. An underpin provides a solid platform for jacking up a concrete foundation at the time of constructing the pin and also later when further jacking is needed. The jack looks like air pump driven on the ground level. What sort of a jack is applicable please? Thanks, Michael
I faced a similar issue with my property in Vic Metro, but underpinning and restumping services came to my aid. Before receiving any quotes, I was strongly advised to consult with an engineer to ensure accuracy.
Thanks for your comment Zu. Thanks for stopping by.
Hi, my name is Ray Clough & i enjoyed reading your underpinning article
My situation is that i am a retired ( of 15 years ) all hands on builder of 40 years in Queensland ( Hervey Bay ) My daughter has a highset building of 3 owners in southwest Sydney that has a corner vertical crack ( 12 – 15 mm wide ) in brickwork at highset level only, after the concrete slab that goes out to face of the bricks around perimeter of building . This is the only serious crack i want to deal with at this time. I was wondering if you had any associates in this Sydney area that you could recommend. This is an unusual request but Sydney`s full of sharks & shonky work, so i was hoping to work with someone i could be more comfortable with there.
If this is something of no interest to you, that’s ok.
Regards Ray Clough 0408256844
I really want to have vest knowledge on underpinning. Why is it done and what can be done to less the cost of it in and already existing building. Thank you
Nice and comprehensive guide to underpinning. thanks.
I like that you mentioned how you can determine if an underpinning contractor is reputable based on what their previous clients have to say about them. My brother is thinking about opening a bakery this fall but worried that the flooring in his building may be unstable since frequent storms cause the footing to shift over time. Maybe he should rely on an experienced professional that can get the job done right.
I was never aware that prior to underpinning services, it is important to get a structural engineer’s evaluation as they will determine the extent of the restoration and will be able to predict the duration it takes. My mother is concerned as she noticed some cracks on the walls of her home. I will advise her to hire a structural engineer so that she will know how to proceed.