Underpinning in Sydney: Taking an existing footing down to ground that will actually hold it
- Designed by a structural engineer, carried out in sequence
- Cracking houses and footings that were never deep enough
- Support for an existing footing before a basement or excavation
- Mass concrete, screw piles or resin, the soil decides
- Cracking on its own does not automatically mean underpinning
Underpinning is the work of taking an existing footing down to ground that will actually hold it. Either because the ground it is sitting on has moved, or because someone is about to dig next to it and it needs support before they do.
We do both across Sydney: houses that have started to crack and move, and commercial work where an existing footing has to be supported before a basement or a boundary excavation goes in next door.
Underpinning is engineered work. It is designed by a structural engineer, it is carried out in a sequence that keeps the building standing the whole time, and it is not something to buy on price alone. Done wrong it makes the problem worse.
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Why a footing ends up needing it
A few reasons come up again and again.
Reactive soil. Clay swells when it is wet and shrinks when it dries. A footing that was fine for thirty years starts moving once a drain leaks, a big tree goes in, or a tree that was drinking the moisture comes out.
Footings that were never deep enough. Common in older housing. They were adequate for the load at the time and are not adequate now, particularly once someone adds a second storey.
Water. A leaking stormwater line or a broken sewer washing fines out from under a footing will undermine it quietly for years.
Someone digging next door. This is the commercial one. If an excavation goes in below the level of an existing footing, that footing has to be supported first. That is not optional and it is not something to discover halfway through the dig.
Cracking on its own does not automatically mean underpinning. Plenty of cracks are cosmetic or have stopped moving. The honest answer often starts with monitoring rather than concrete, and we will say so if that is what we think.
Mass concrete, piles or resin
Three broad methods, and the right one depends on the soil, the load and the access.
Mass concrete underpinning. The traditional method. A pit is excavated under a short section of the footing, down to competent ground, and filled with concrete, then the next section, and so on. Slow, proven, and it works where access is tight because the plant is small.
Screw piles. Steel piles wound into the ground and bracketed to the existing footing. Good where you need to get down deep, where the soil is soft for a long way, or where you want the load transferred quickly with less excavation.
Resin injection. Expanding resin injected into the ground to fill voids and lift. Fast, minimal mess, and genuinely useful in the right conditions. It is not a structural footing though, and it is sold as a cure for things it does not cure. We will tell you when it is the right tool and when it is not.
What decides it is the geotechnical information, not a preference. If nobody has taken a look at what the soil is doing, that comes first.
Supporting a neighbouring footing before you excavate
If you are a builder about to dig a basement on a tight site, this is the part that holds up your programme if it is left late.
Where your excavation goes below the neighbouring footing, that footing has to be underpinned or otherwise supported before you get anywhere near it. It needs an engineer's design, it usually needs a dilapidation report on the neighbouring property before a tool is picked up, and depending on the jurisdiction it may need formal notice to the adjoining owner.
We do this work as part of the early works package, alongside the demolition and the bulk excavation, so it is sequenced properly instead of being a separate trade turning up late. If you are pricing a job now and the geotech shows the neighbour is founded higher than your basement, talk to us at tender stage, not at excavation stage.
Why the sequence is the whole job
You never excavate the whole length of a footing at once. The wall would have nothing under it.
The work goes in a hit and miss sequence: a short section is taken out and supported, the next section left untouched, and you come back for it once the first has gained strength. The engineer sets the pin lengths and the order. Following that sequence is the difference between a building that is supported throughout and a building that cracks while you are working on it.
This is why underpinning is not fast and why anyone quoting you a very quick turnaround is worth a second question. It also means the site has to be kept clean and the propping has to be right, because people are working in open pits under a loaded wall.
Frequently asked
Do I definitely need underpinning? Maybe not. Get the cracking assessed first. Monitoring over a few months often shows movement has stopped, and then you are patching, not underpinning.
Do you do the engineering? The design comes from a structural engineer. We work to that design and we can point you to engineers we work with regularly if you have not got one.
Can we stay in the house? Usually yes. The work happens outside and below. It is noisy and there will be spoil, but people generally stay put.
Will insurance cover it? Sometimes, depending on the cause. Damage from a burst pipe is treated very differently to gradual soil movement. Worth asking your insurer before you commit.
What about the neighbour? If the work is near or on the boundary, they need to be dealt with properly, and a dilapidation report protects you as much as them. We do that as standard.
Talk to someone who has actually priced one
Tell us the address and what you are trying to end up with. We will tell you straight whether it is a full removal or a partial, what access you have got, and what it will cost. No obligation.
Call 02 7908 4944 or fill in the form at the top of the page and we will call you back. We cover Sydney and the surrounding region.
Perfect Stripout & Demolition acknowledges the Aboriginal and Torres Strait Islander people as Traditional Custodians of the country on which we live and work. We pay our respects to the Traditional Custodians and Elders past, present and future, and honour their connection to the land and ongoing contribution to society.