Underpinning methods compared by an independent engineer

Search for screw piles, resin injection or helical piers and many of the results come from companies that install them. That's natural, but it means many comparisons are written by someone with a method to sell. This guide compares the main underpinning methods from the engineer's side: how each one works, where it can suit, how it can fail and what an engineer checks before signing off. For the basics, start with what underpinning is. If your house sits on stumps, read underpinning vs restumping first.

Underpinning methods: quick facts

Main methods

Mass concrete, bored piers, screw piles, resin injection, slab jacking

What decides

The cause of the movement, the soil and the footing

Down to firmer ground

Mass concrete, bored piers and screw piles

Work in the soil

Resin injection; slab jacking lifts a slab by injection

Shared weak point

A cause that isn't fixed, such as a leak or a tree

Our role

Compare, design and certify. We sell no method.

How do the underpinning methods compare?

Here are the five main methods side by side: how each works, where it can suit, its limits and when it can fail, and what the engineer checks. None of them is our product, and the "can suit" column is general engineering guidance, not a recommendation for your house.

General guidance only. Each method suits different soils and causes, none suits every house, and the right one for yours depends on an inspection and, sometimes, a soil investigation.

How does mass concrete underpinning work?

Mass concrete underpinning extends the footing down to firmer ground with concrete. The ground beside and under the footing is dug out in short sections, so the wall above stays supported, and concrete is cast under the footing in each one. Each section is packed tight to the old footing before the next is dug.

It can suit houses where firmer ground is a moderate depth down and there's room to dig. Where firmer ground is deep, the excavation gets slow, disruptive and costly, and another method may suit better. The weak point is the base: a pad that stops short of firmer ground, or sits on clay that keeps shrinking and swelling, can keep moving with the house.

What are bored piers, and when do they suit?

Bored piers, also called concrete piers, are holes drilled down to firmer ground and filled with concrete, then tied into the house, often with a new beam or brackets under the footing. They can reach deeper than mass concrete practically can.

The trade-offs are access and ground conditions. A drilling rig has to reach each pier position, and wet or collapsing soil can complicate the drilling. Like every pier or pile, a bored pier only works if it reaches a suitable layer and is properly connected to the existing footing, which in an older house may be shallow or weak itself.

Screw piles and helical piers: how do they work?

Screw piles, also called helical piers or screw piers, are steel shafts with helical plates that are screwed into the ground until they reach a firmer layer. They're then tied to the footing with brackets or a new beam. Little excavation is needed, and the installation equipment can suit tighter sites.

Their weak points are underground. A pile can stop on rock, rubble or old fill and look finished without reaching the layer the design relies on, and steel needs suitable corrosion protection in some soils. Installers often record how hard each pile was to turn, the installation torque, as a check on capacity, and the engineer reviews those records against the design.

Resin injection: what is chemical or resin underpinning?

Resin injection, also called chemical or resin underpinning, pumps expanding polyurethane into the soil under a footing through small injection tubes. The resin fills voids, densifies the soil and can sometimes lift the footing back towards level. There's no large excavation, and the work can be quick.

Its limits come from what it does. Resin improves the soil it reaches, rather than carrying the load down to deeper ground the way piers and piles do. Where movement comes from deeper soils, or from reactive clay that keeps shrinking and swelling with the seasons, it may not be the right fit. Lifting also needs control: lifting too far or too fast can open new cracks.

What is slab jacking?

Slab jacking lifts a concrete slab back towards level by injecting material beneath it, such as resin or grout. It's aimed at slabs that have sunk, for example over voids or poorly compacted fill.

It only makes sense if the slab actually sank. On reactive clay, part of a slab can heave instead: edge heave and centre heave describe where the lift is. A slab that looks low at the edges may have risen in the middle, and jacking the edges up to match could be the wrong fix. A floor level survey and a diagnosis come first. Read more in reactive clay and slab heave.

When does each underpinning method fail?

Every method can fail, and the reasons overlap more than you might expect. These are the main ones, stated generally: whether any applies to your house needs an inspection. For the causes behind the movement itself, see house subsidence and movement.

How does an engineer choose the right method?

By working backwards from the cause. The process is the same whichever method ends up on the drawings.

1. Step 1

   Inspect the house

   Cracks are measured and rated against the AS 2870 damage categories, and doors, floors, drainage, plumbing, trees and site conditions are checked.

2. Step 2

   Diagnose the cause

   Why did the footing move? Sometimes a geotechnical soil investigation or a plumbing test is needed first.

3. Step 3

   Deal with the cause

   Leaks, drainage and trees are fixed or managed, so the repair isn't fighting the same problem.

4. Step 4

   Choose and design the method

   The methods that suit the soil, the footing and the cause are compared, and the one that fits is designed.

5. Step 5

   Document it for the permit

   The design documents go with the application for the building permit or approval.

6. During and after

   Inspect and certify

   The critical stages are inspected while the work is built, and the finished work is certified.

Any licensed contractor can build the design, so you can compare quotes on the same scope. Our underpinning design and certification covers each step, and do I need an engineer for underpinning? explains when an engineer's design is needed. If you're still at the cracks stage, start with a foundation and crack report or our guide to cracks in walls.

What do the different underpinning methods cost?

Published guides price each method in different units, so the figures don't compare directly. All were checked 8 October 2026, and none are our prices.

• Mass concrete: $1,000–$3,000 per linear metre of wall (Remedial Building Help, citing Mainmark's published figure)
• Piers: about $2,500–$5,000 each (QuickQuote)
• Screw piles: $250–$500 per m² as an area guide (a Melbourne contractor's guide)
• Resin injection: $4,000–$16,000 per job (Buildfix, a resin contractor)

The total depends on how many metres, piers or square metres the design calls for. See the underpinning cost guide for whole-job ranges, what drives the price and engineer fees.

Why don't we sell any underpinning method?

Because the method should follow the diagnosis. We don't sell any method, we don't install anything and we don't recommend contractors. We're paid for the engineering whichever method the design uses, so there's nothing to gain from steering you to one.