Underpinning is what most people picture when they hear “subsidence”: the house dug around, foundations deepened, months of disruption. In reality, most subsidence is fixed without underpinning at all. The key is working out what’s causing the ground to move, and whether taking that cause away will stop it.
The principle: stop the cause, then repair
Subsidence happens because something is disturbing the ground under the foundations. If you can identify and remove that cause, the ground often stabilises on its own, and the building can then be repaired. Underpinning is reserved for cases where the cause can’t be removed, or where the ground won’t recover.
Fixing subsidence without underpinning
The common routes are:
Dealing with trees and vegetation
Where clay shrinkage caused by tree roots is the problem, removing or reducing the tree (subject to permissions, tree preservation orders and conservation area rules) takes away the moisture demand. The clay then gradually rehydrates and the movement stops. A monitoring period follows to confirm it. Removing a large, established tree can itself cause heave as the clay swells, which is why this needs professional judgement rather than a chainsaw.
Repairing drains
Where a leaking drain has washed out or softened the soil, repairing or relining the drain removes the cause. The softened ground may need time to recover, and in some cases localised ground treatment.
Monitoring
Before repairs, insurers and engineers usually monitor the building over a period, often through at least one full seasonal cycle, measuring crack widths and levels to confirm the movement has stopped. It feels slow, but repairing a building that’s still moving just means doing it twice.
Superstructure repairs
Once movement has stopped, the visible damage is repaired: crack stitching with helical bars bonded into the mortar joints, rebuilding badly damaged sections of wall, resetting windows and doors, and redecorating.
When underpinning genuinely is needed
Underpinning is usually reserved for situations where:
- the cause can’t be removed — for example, a tree on a neighbour’s land that can’t be dealt with, or a mining or ground condition issue;
- the foundations are too shallow for the ground conditions, and the building will keep moving whatever else is done;
- the ground has been so badly disturbed that it won’t recover adequately;
- movement has continued after the cause was dealt with.
Types of underpinning and ground stabilisation
Where stabilisation is needed, there’s more than one way to do it:
- Mass concrete underpinning — the traditional method, excavating in sections beneath the existing foundation and filling with concrete to reach stable ground.
- Piled underpinning — mini-piles taken down to stronger strata, with beams or needles transferring the building’s load onto them. Often used where good ground is deep.
- Resin injection — expanding resins injected into the ground to fill voids and strengthen weak soil. Less disruptive, but suited only to certain ground conditions.
- Partial underpinning — only the affected section of foundation is treated, which is more common than whole-house underpinning.
What drives the cost of fixing subsidence
The cost varies enormously with the solution:
- Cause removal (tree work, drain repair) is usually the cheapest route.
- Monitoring adds time rather than much cost.
- Superstructure repairs depend on the extent of cracking and rebuilding.
- Underpinning is the most expensive, and depends on the length of foundation, the depth to stable ground, the method, and access.
If you’re insured, most of this is typically handled through your buildings policy, subject to the excess. We explain what insurance usually covers separately.
Why getting the cause right matters
The expensive mistakes in subsidence are nearly always diagnostic: underpinning a house whose real problem was a leaking drain, or repairing cracks while the cause is still active. A clear understanding of what subsidence is and a careful investigation of cause come first.
Our subsidence assessment is built on extensive claims experience and focuses on cause, whether movement is ongoing, and whether the proposed fix actually matches the problem. Get in touch if you’re facing a subsidence repair or buying a house that’s had one.