Chosing The Right Method For Fixing Subsidence
When subsidence strikes, the pressure to act fast is real — but choosing the right repair method matters just as much as how quickly you move. Get it wrong, and you risk a second failure, a rejected insurance claim, or a building control sign-off that never comes. The two leading repair methods in the UK — traditional underpinning and helical screw piles — differ significantly in cost, disruption, speed, and long-term durability. This guide compares both in practical detail, so you can make an informed decision alongside your structural engineer or building control officer.
What Causes Subsidence?
Subsidence is the downward movement of the ground supporting a foundation, and in the UK it’s rarely caused by one thing alone. The most common culprit, particularly across London and the South East, is clay shrinkage: reactive clay soils lose moisture during dry spells and shrink, leaving foundations unsupported. Even a small volume change can cause measurable settlement and visible cracking.
Tree roots are another major factor. Large trees can draw moisture from clay subsoils many metres from the trunk, and a mature specimen can remove tens of thousands of litres of water from the ground each year — moisture loss that can trigger localised subsidence beneath a nearby extension or bay window. Less commonly, subsidence results from soil washout, where leaking drains or natural springs erode fine soil particles and create voids beneath the surface.
Understanding the cause matters because the wrong repair can mask the symptom without addressing the underlying problem — and a repair that isn’t matched to the ground conditions can fail again within a few years.
Traditional Underpinning: The Established Method
Traditional underpinning involves excavating below the existing foundation in short, staged sections, then pouring concrete to create a new, deeper base tied into competent ground. It’s a proven approach with a long track record, but it comes with real practical costs. Excavation is sequential — you can’t dig adjacent sections simultaneously without temporarily losing support — so even a modest semi-detached property can take three to eight weeks to complete, longer if groundwater, poor access, or unforeseen ground conditions intervene.
The disruption is significant: excavated spoil has to be stored or removed, access is needed for machinery and concrete delivery, and party wall agreements are often required where work sits close to a neighbouring property. Dewatering, temporary shoring, and full reinstatement of gardens or paving can add materially to both the timeline and the final bill.
Screw Piles: A Faster, Cleaner Alternative
Helical screw piles — specifically the AB Chance system that Ground Sun installs — take a fundamentally different approach. Rather than excavating unstable ground, a steel shaft with helical plates is screwed directly into the earth using hydraulic torque until it reaches stable, load-bearing strata. There’s no excavation, no concrete curing time, and minimal disruption to gardens, driveways or access routes.
Installation is dramatically faster: most domestic subsidence repairs are complete in one to three days, compared with weeks for traditional underpinning. AB CHANCE® screw piles are supported by established technical data and can be designed to meet relevant structural and Building Control requirements, subject to project-specific approval. The system can also be designed for a long service life in challenging soils such as London clay, with durability supported by galvanised steel construction and appropriate corrosion protection. Because the equipment is compact, screw piles are especially suited to restricted-access sites where traditional machinery simply won’t fit.
Comparison at a Glance
| Factor | Traditional Underpinning | Screw Piles (AB Chance) |
|---|---|---|
| Installation time | 3–8 weeks | 1–3 days |
| Ground disturbance | High — excavation required | Minimal — no excavation |
| Design life | 50–100 years | 150 years (London clay) |
| Access requirements | Full excavation access | Works in restricted spaces |
| Regulatory approval | Subject to Building Control approval | Can be designed to meet Building Control requirements, subject to project-specific approval |
| Typical cost | £15,000–£50,000+ | Often comparable or lower |
This makes screw piles particularly relevant when managing ground movement on London clay or working on tight-access urban sites where excavation isn’t practical.
Frequently Asked Questions
How do I know if I need underpinning or screw piles?
A structural engineer or chartered surveyor first confirms the presence and cause of subsidence, then recommends a repair method suited to your ground conditions, access, and budget.
Are screw piles as strong as concrete underpinning?
Yes. AB Chance screw piles are engineered and load-tested to the same structural standards as traditional underpinning, with independent third-party certification confirming their capacity.
How much does fixing subsidence typically cost?
Traditional underpinning generally costs £15,000–£50,000 or more, depending on depth and access. Screw piles are often comparable or lower, particularly on restricted or awkward sites where excavation costs escalate.
Will my insurer or warranty provider accept screw piles?
Potentially, yes. Acceptance will depend on the individual project, the supporting technical documentation, the structural design and the requirements of the insurer or warranty provider. AB CHANCE® screw piles are supported by established technical data and can be designed to meet relevant project requirements.
Can screw piles be used near protected trees?
Yes. Their minimal ground disturbance makes them well suited to root protection zones, where excavation-based methods would risk damaging root systems.
How long does a screw pile subsidence repair take from start to finish?
Most domestic projects, from site assessment to completed installation, take between three and five days — a fraction of the time required for traditional underpinning.
About Ground Sun
Ground Sun is a UK piling contractor specialising in helical screw pile foundations, underpinning, and ground engineering, working nationwide with structural engineers, developers, and local councils. As the exclusive UK and European distributor of AB CHANCE® systems, we provide fully engineered solutions — from initial design and load testing through to installation — covering subsidence repair, restricted access piling, and new build foundations. Our team combines decades of technical expertise with a track record of navigating building control and insurer requirements smoothly. Learn more about our approach at London Screw Piling.
Subsidence Repair Services
Ground Sun provides specialist solutions for subsidence repair in buildings using AB Chance helical screw pile systems. This offers a low-disruption alternative to traditional underpinning, helping stabilise affected structures with reduced excavation, low vibration and faster installation. Their approach is suited to challenging ground conditions, restricted access sites and projects requiring proven structural performance.
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