When underpinning is needed
Slab and full-brick homes rely on the soil under their footings staying put. When part of that soil gives — reactive clay shrinking in drought, a leaking pipe softening one corner, a tree drying out the ground on one side — that section of footing drops and the structure above it cracks. Underpinning extends or re-supports the footing so it bears on something stable: deeper soil, piles, or engineered resin.
The tell-tale pattern is stepped or widening cracks in brickwork, doors and windows out of square on one side of the house, and gaps opening between floors and skirtings — usually worst at one corner. The signs of subsidence guide walks through the full checklist.
When it isn't
Most cracking never needs underpinning. New homes settle for a year or two; render and plaster craze cosmetically; seasonal hairlines open in summer and close in winter. Underpinning is for progressive, structural movement — and because it's expensive, it attracts overselling. The rule of thumb: monitor first, get an independent opinion second, and only then talk to contractors. Our guide "Do I actually need underpinning?" is the place to start if you're unsure.
The three main methods
Mass concrete — the traditional approach: excavate under the footing in sections and pour new concrete pads. Proven, disruptive, priced per metre. Screw piles — steel piles wound into stable soil below the problem layer, then connected to the footing by brackets; suits deep reactive clay and poor access. Resin injection — engineered resin pumped under the slab that expands and re-compacts the soil; minimal digging, fast, and increasingly common for slab-on-ground homes, though not right for every soil. The methods comparison covers which suits what.
What it costs
Realistically $10,000–$40,000 for most residential jobs, priced per linear metre of footing or per pile/injection zone rather than per stump. The spread is wide because methods differ so much — see the underpinning cost guide for ranges by method and the factors that move them.
What to do first
Photograph and date the cracks, then measure the widest points. If cracks exceed 5 mm, keep growing, or come with doors out of square, commission an independent assessment — a structural engineer's report (roughly $600–$1,200) tells you what's actually moving and what fix is justified, before any contractor with a product to sell gets involved. Engineer's reports explained. Insurance rarely covers gradual settlement but sometimes covers sudden causes like burst pipes — check before you claim.
Ready to find out what it'll cost?
Up to three quotes from licensed local firms. Free, no obligation.
Common questions
Is underpinning ever urgent?
Rarely in the emergency sense — houses move in months and years, not hours. But fast-growing cracks (visible change within weeks) justify getting an engineer promptly, because early intervention is cheaper than late.
Will underpinning fix the cracks?
It stops the movement that causes them. The cracks themselves still need patching and repainting afterwards, and badly displaced brickwork sometimes needs rebuilding — make sure quotes say which side of that line they cover.
Does underpinning affect resale?
A documented, engineer-certified underpin generally reassures buyers more than unexplained cracking does. Keep the engineering report, the contractor's warranty and any council paperwork together for the sale file.
Can tree roots really sink a house?
Indirectly, yes — large trees close to footings dry out clay soils and shrink them. Sometimes managing the tree and the drainage stabilises things without underpinning at all; a good engineer will tell you.