Underpinning methods compared

The three families

Mass concrete underpinning is the traditional method: crews excavate pits beneath the existing footing in a staged sequence and fill each with concrete, extending the footing down to firmer ground. It is simple and proven, but labour-heavy. Our mass concrete guide covers it in detail.

Screw piles are galvanised steel piles wound into the ground beside or beneath the footing until they hit a set resistance, then connected with brackets so the building's load transfers to deep, stable soil. They reach depths hand excavation never could; see the screw piles guide.

Resin injection pumps an expanding structural resin into the soil beneath a slab or footing through small drilled holes; the resin fills voids and compacts the surrounding ground, often lifting the structure back towards level. It is the least disruptive family and the most dependent on suitable soil, as the resin injection guide explains.

How the costs compare

Comparing quotes is awkward because each family charges in different units. Mass concrete is typically priced per metre of wall underpinned, around $2,000–$5,000 per metre. Screw piles are priced per pile, roughly $3,000–$7,000 each, and most jobs need several. Resin injection is usually quoted as a whole-of-problem price, commonly $8,000–$25,000. That means a short run of one method can cost more or less than a large job in another, so always compare quotes on total scope, not headline rates. Whatever the method, most residential underpinning lands between $10,000 and $40,000; our costs guide breaks the ranges down.

Which method suits which problem

• Stable soil at modest depth: mass concrete works well when firm ground sits within practical digging reach, and it suits older homes with strip footings and good access.
• Deep reactive clay: screw piles shine where the soil keeps moving near the surface, because they carry the load down below the seasonal movement zone entirely.
• Slab-on-ground with voids or compactable soil: resin injection suits slabs that have dropped over loose fill, washed-out soil or shallow voids, where compacting the ground and re-levelling the slab solves the actual problem.

Access matters too. A tight inner-city block may rule out machinery, favouring hand-dug mass concrete or compact pile rigs, while a fragile heritage building may favour the low-vibration options.

Disruption and timelines

Mass concrete is the slowest and messiest: staged excavation, spoil removal and concrete cures typically stretch over one to several weeks, and gardens or paving along the wall rarely survive untouched. Screw piles usually take days rather than weeks, with disruption concentrated where the rig needs access. Resin injection is often finished in a day or two through holes about the size of a coin, with no excavation, and you can generally stay in the house throughout. None of the three normally requires you to move out.

Diagnosis first, product second

Most underpinning companies specialise in one family, which means a free inspection tends to end in a quote for whatever that company sells. The method should be chosen the other way around: an independent engineer's report identifies why the house is moving and specifies the fix, sometimes concluding that no underpinning is needed at all once drainage or plumbing is repaired.

Real jobs are also messier than brochures. Mixed-method work is common: screw piles under a dropped corner where clay runs deep, with resin injection re-levelling the slab in the middle of the house. An engineer can specify that combination; a single-product salesman cannot.