Does Your House Need Underpinning, or Just Crack Repair?

A few hairline cracks in your plaster rarely mean your footings are failing — most are seasonal movement or old paint cracking that a tube of filler will fix. Genuine underpinning, where piers are driven under failing footings to stop a wall dropping further, typically costs $9,750 – $16,300 (around $12,500 for a typical job), so it pays to work out which one you've actually got before anyone touches your foundations.

Cosmetic cracking vs real movement

Almost every house moves a little with the seasons, especially on Australia's reactive clay soils, which swell when wet and shrink when dry. That movement opens and closes fine cracks that are annoying but not dangerous. The problem is that genuine footing failure — a sinking pier, a leaking stormwater pipe washing out the soil under a slab, a tree root drawing moisture from under one corner — also shows up as cracking, and from across the room the two can look identical. The signs below are what separates them.

Signs that usually point to real movement

• Cracks wider than about 5mm, or ones you can fit a 10-cent coin into.
• Diagonal "stair-step" cracks in brickwork running from the corner of a door or window, especially if they're wider at one end than the other.
• Doors and windows that have gone out of square — not just sticking, but visibly crooked in the frame, or a door that now drags on the floor on one side only.
• Cracks that keep getting wider when you check them every few months, rather than opening and closing with the weather.
• A visible slope across a floor, checked with a spirit level or a marble that consistently rolls one way.
• Cracking on only one side or corner of the house, which points to localised footing movement rather than general settling.

Any one of these is a reason to get a structural engineer's report before you do anything else — not a builder's opinion, an engineer's.

Signs that are usually cosmetic

• Fine, hairline cracks in plaster or cornice joints that appear in the first year or two after a house is built, as timber and plaster dry out.
• Cracks that open slightly in a dry summer and close again over winter — classic reactive-clay movement that's cosmetic unless it's progressively getting worse.
• Cracking confined to a rendered or painted finish, with no matching crack in the brickwork or structure underneath.
• Doors that stick only in humid weather and free up again later.
• Uniform, thread-like cracks spread evenly across a wall, rather than concentrated at one corner or opening.

If your cracking matches this list, you're very likely looking at a render or paint job, not underpinning. If it's only the render that's affected, repairing or re-coating it is a different, far cheaper job — see our Rendering guide for what that typically costs.

What underpinning actually costs, by scope

Underpinning jobs are priced largely by how many piers are needed and how deep they have to go, which is why the range is wide:

Tier	Typical cost	What's usually involved
Basic	$9,600	A handful of piers under one affected section, resin or concrete underpinning, shallow or moderate depth
Mid-range	$12,500	A fuller set of piers (our estimates are based on 8 as a typical count), engineer design and sign-off, standard soil conditions
Premium	$16,800	Extensive underpinning across multiple walls, deep piers, difficult access or poor soil requiring specialist techniques

We build these figures from labour hours on a job of this size, priced at local trade rates, plus materials, then check the result against market prices and real quotes — not a single national average. The Underpinning guide has the full breakdown of what drives the price up or down on your job, including soil type, pier depth and access.

Why it's worth getting the diagnosis right first

Underpinning is one of the most expensive single repairs you can do to a house, and it's not reversible — once piers are in, they're in. Paying for it on cosmetic cracking is money wasted; skipping it on genuine footing failure lets the problem get worse and more expensive. A structural engineer's inspection and report costs a small fraction of the underpinning job itself, and it's the only way to know which category you're actually in. Ask the engineer to specify the cause (not just "underpinning needed") — a leaking pipe or poor drainage around the footings sometimes turns out to be the real fix, at a fraction of the cost.

Once you do have a scope from an engineer, get it priced by more than one underpinning contractor, and run any quote through our "is my quote fair" tool before you sign — pier counts and depths vary enough between contractors that the same job can come back at very different prices. If drainage or regrading around the house is part of the fix, it's also worth checking whether a New driveway or paving job nearby is contributing to water pooling against the footings, since that's a common and much cheaper cause of movement that gets blamed on the foundations themselves.