If your property has subsidence, you'll likely be presented with two main repair options: traditional underpinning or geopolymer resin injection. Both work. Both are permanent. But they differ enormously in cost, disruption, and applicability — and the right choice depends heavily on your specific ground conditions.
This guide gives you the information you need to have an informed conversation with your engineer or insurer.
How Each Method Works
Traditional underpinning extends your existing foundations deeper into stable ground. Sections of earth beneath the existing foundation are excavated in sequence, and new mass concrete is poured to create a deeper footing. It's a proven method used for over a century.
Resin injection stabilises the ground itself. A two-part geopolymer resin is injected through small (16mm) holes drilled from the surface. The resin expands underground, filling voids, compacting loose soil, and increasing the bearing capacity of the ground beneath the foundation. Real-time laser monitoring tracks movement during injection.
Head-to-Head Comparison
| Factor | Resin Injection | Traditional Underpinning |
|---|---|---|
| Typical cost | £3,000–£8,000 | £10,000–£30,000+ |
| Duration | 1 day (4–6 hours on site) | 2–8 weeks |
| Excavation | None | Significant |
| Can you stay at home? | Yes | Usually yes, but more disruptive |
| Noise and mess | Minimal | Considerable |
| Depth of treatment | Up to ~6m | Unlimited |
| Soil types | Clay, granular, mixed | All types |
| Severity | Mild to moderate | Moderate to severe |
| Monitoring | Real-time laser | Post-completion surveys |
| Environmental impact | Low — inert materials | Higher — concrete and excavation |
When Resin Injection Is the Better Choice
Resin injection is ideal for the majority of residential subsidence cases in Hertfordshire, particularly:
- Clay shrinkage subsidence — the most common type across Watford, Bushey, Borehamwood, and southern Hertfordshire
- Properties you want to sell quickly — treatment is completed in a day with certification available shortly after
- Insurance claims — insurers increasingly prefer resin injection because it's faster, cheaper, and equally effective for appropriate cases
- Occupied properties — no need to move out, no excavation in the garden, no skip on the drive for weeks
When Traditional Underpinning Is Necessary
Underpinning becomes the right choice when:
- The subsidence is severe — foundations have dropped significantly and need to be physically extended to stable ground
- The ground conditions are very poor — deep soft soils, made ground, or large voids that resin alone cannot address
- The property needs a deeper foundation — for example, if you're adding a basement or significantly increasing loads
- Resin injection has been ruled out — after a site investigation shows the ground isn't suitable
What About Hertfordshire Specifically?
Much of Hertfordshire sits on London Clay, which is the single most common cause of subsidence in the UK. Clay shrinkage responds extremely well to resin injection — it's the treatment method most commonly used in the county.
However, areas with more complex geology need careful assessment:
- [Rickmansworth](/locations/rickmansworth) and river valley areas — alluvial deposits can be variable
- [Royston](/locations/royston) and north Hertfordshire — chalk dissolution may create voids better suited to void filling
- [Hertford](/locations/hertford) — multiple river confluences create mixed ground that needs bespoke solutions
This is exactly why a proper site investigation matters. Any engineer who recommends a solution without surveying the ground first should be treated with caution.
Cost Breakdown: A Typical Hertfordshire Semi-Detached
To make the comparison tangible, here's what each method typically costs for a standard 3-bedroom semi with subsidence affecting one corner:
| Cost Element | Resin Injection | Underpinning |
|---|---|---|
| Survey and design | Included | £1,500–£2,500 |
| Groundworks | N/A | £3,000–£5,000 |
| Materials and labour | £4,000–£6,000 | £8,000–£15,000 |
| Monitoring | Included (real-time) | £500–£1,000 |
| Cosmetic reinstatement | Minimal | £1,000–£3,000 |
| Total | £4,000–£6,000 | £14,000–£26,500 |
These are indicative figures — every project is different. We provide fixed quotes after a free survey.
Making the Decision
In our experience across hundreds of Hertfordshire projects, roughly 70–80% of residential subsidence cases are suitable for resin injection. The remaining cases genuinely need underpinning or a combination approach.
The key is getting the diagnosis right first. A proper investigation — including ground conditions, the extent of movement, the building's structure, and the cause of subsidence — determines which method will work. We always recommend the least invasive effective solution.
Get a free survey and find out which method is right for your property →