Guide
Underpinning vs resin injection
By Structural Repairs UK · Updated 2026-11-09
Underpinning strengthens a building’s foundations by taking them down to firmer ground, while resin injection stabilises the existing ground by injecting an expanding resin beneath the foundations. Which fits depends on the soil, the depth of firm ground, access and the engineer’s diagnosis, and many subsidence problems need neither.
Do I need underpinning at all?
Often you do not. Most subsidence claims are fixed without underpinning, because the cause, usually a leaking drain or a thirsty tree on clay, can be dealt with and the building then stops moving. Foundation work is used where movement continues after the cause is tackled, where the cause cannot be removed, or where the foundations are clearly inadequate. An independent chartered structural engineer should make that call after investigation and, often, monitoring, and we can arrange this.
What is traditional mass-concrete underpinning?
Mass-concrete underpinning means digging out short sections beneath the existing foundation, one at a time, and filling each with concrete down to firmer ground. It is the oldest method and suits shallow problems where good bearing ground is not too deep. It is labour-intensive and messy around the dig, but needs little specialist plant. Underpinning a small section usually takes about a week. The guide price is £1,000 to £1,500 per metre of wall inc VAT.
When are beam-and-base and mini-piling used?
Beam-and-base and mini-piling are used when firm ground is too deep for mass concrete to be practical. Beam-and-base uses a reinforced concrete beam under or in place of the old foundation, carried on concrete bases at intervals, at a guide £1,500 to £2,500 per metre of wall. Mini-piling bores or drives small piles down to firm strata, often well below the clay, and links them with a beam. It suits deep clay, poor fill or nearby trees, usually takes 2 to 4 weeks, and is a guide £2,000 to £3,500 per metre.
How does resin injection work?
Resin injection stabilises the ground under a foundation by injecting an expanding resin through small holes, often from outside. As it expands it fills voids and compacts loose soil, and under careful level monitoring it can lift a dropped foundation slightly. It suits loose, granular or made ground, and voids from washed-out drains, more than deep shrinkable clay. Work on site usually takes 1 to 2 days. The guide price is £800 to £1,500 per metre of wall treated, with typical domestic projects at £5,000 to £15,000.
Which method causes the least disruption?
Resin injection is usually the least disruptive, because it needs only small drill holes and often no digging inside the house. Traditional underpinning means excavating along the affected walls, removing spoil and sometimes lifting floors where work runs inside. Mini-piling uses compact rigs that can work in tight spaces but is noisy while the piles go in. Beam-and-base sits between the two. In most cases you can stay at home during the work, although rooms beside the dig may be out of use for a time.
How do the costs and timescales compare?
Resin injection is usually the quickest on site and among the cheapest per metre, while mini-piling costs most. The figures below are 2026 guide prices inc VAT; they vary by region and access and are confirmed in writing after a survey. The total depends on how many metres of wall need treating, the depth to firm ground and how easy the site is to reach. Engineer’s design and building control fees for an underpinning scheme add a guide £800 to £2,500 on top of the work itself.
- Mass-concrete underpinning: £1,000 to £1,500 per metre
- Beam-and-base underpinning: £1,500 to £2,500 per metre
- Mini-piled underpinning: £2,000 to £3,500 per metre, 2 to 4 weeks
- Resin injection: £800 to £1,500 per metre, 1 to 2 days on site
- Larger domestic underpinning schemes: 3 to 6 weeks
What approvals does underpinning need?
In England and Wales, underpinning is building work under Part A of the Building Regulations and needs building control approval and inspections. Underpinning a party wall, or digging near a neighbour’s foundations, usually needs notice under the Party Wall etc. Act 1996. In Scotland, structural work generally needs a building warrant before it starts and a completion certificate afterwards. In Northern Ireland, council building control applies. Ask whether resin injection needs approval in your case. We deal with building control where the work needs it.
Questions about this guide
Is resin injection as good as underpinning?
Resin injection is not better or worse than underpinning, just suited to different ground. It works well for loose or made ground and voids under foundations, with little disruption. Deep shrinkable clay, or movement driven by large trees, often needs foundations taken deeper by underpinning or mini-piling. Your engineer will confirm which method suits the soil found in trial pits or boreholes.
Can I stay in my house during underpinning?
In most cases you can stay in your house during underpinning, especially when the work is outside. Expect noise, dust and restricted access on the affected side. Where work runs under internal walls, floors may need lifting and some rooms may be out of use for a while. You should be told the sequence and the rooms affected before work starts.
Does underpinning affect selling a house?
Underpinning usually needs to be disclosed when you sell, and a buyer’s lender will ask for the paperwork. Keep the engineer’s design, the building control completion certificate and any certificate of structural adequacy. With good paperwork, a properly underpinned house is often easier to sell than one with unexplained movement. A surveyor or solicitor can advise on a particular sale.