Guide
Clay soil subsidence in the UK
By Structural Repairs UK · Updated 2026-11-09
Clay soil subsidence happens when shrinkable clay beneath a building dries out, shrinks and lets the foundations drop, and it is the most common cause of subsidence in the UK. It is most frequent on the high-plasticity clays of London and the South East, but shrinkable clays occur across much of England and parts of Wales.
Why does clay soil cause subsidence?
Clay causes subsidence because it changes volume as its moisture content changes. Clay is made of very fine particles that hold water. When it dries, it shrinks and can crack, and when it wets again, it swells. Foundations sitting in the upper few metres of clay move with it. High-plasticity clays shrink and swell the most. Sand, gravel and rock do not behave this way, which is why the same weather can damage a house on clay and leave one on gravel untouched.
Where are shrinkable clays found in the UK?
Shrinkable clays are most widespread in southern and eastern England and the Midlands. The main clays are listed below, though local conditions vary a great deal, and the ground under a single house can differ from a regional map. Other clays occur elsewhere, and thin layers of clay can sit beneath other deposits, so a site check matters more than a postcode.
- London Clay: London and the South East, the most susceptible area
- Oxford Clay: a band from Dorset to North Yorkshire, including Oxford, Bedford and Peterborough
- Gault Clay: East Anglia through Wessex, and around the Weald in Kent, Surrey, Hampshire and Sussex
- Mercia Mudstone: the Midlands, Cheshire and Merseyside, generally with fewer serious problems
Why do dry summers matter so much?
Dry summers matter because they dry clay more deeply than usual, especially where trees are drawing water at the same time. Shrinkage is usually worst in late summer and early autumn, after months of high water use and little rain. After a long, hot, dry summer, many more households notice new cracks, sticking doors and gaps at skirting boards. Most clay movement is seasonal, so cracks may partly close again over a wet winter, which is why monitoring often covers a full year.
How can I check the soil under my house?
You can get a general idea from geological maps. The British Geological Survey publishes maps and data on ground conditions, including the potential for clay shrinking and swelling, and some of this is free to view online. Conveyancing searches and insurers often draw on similar data. These sources describe broad areas, not your plot, so they cannot confirm what is under your foundations. Only a site investigation, such as a trial pit or borehole with soil testing, does that.
Does living on clay mean my house will suffer subsidence?
No. Living on clay raises the risk, but most houses on clay never have a serious subsidence problem. Foundation depth, nearby trees, drain condition and the type of clay all matter. Newer houses on clay are usually built with deeper foundations, set with nearby trees in mind. Older houses with shallow footings, and lighter parts of a building such as bays, porches and extensions, are more often affected. Clay is a reason to watch for signs, not a reason to assume damage.
What can I do to reduce the risk on clay?
You can reduce the risk on clay by keeping drains in good order, managing trees and shrubs near the house, and acting early on new cracks. Leaking drains can soften clay or wash out fine material, so fix gutters, downpipes and gullies that overflow. Avoid planting thirsty trees close to the house, and get advice before removing large ones, because heave can follow on clay. Keep dated photos of any cracks, and tell your insurer before permanent repairs start if you suspect subsidence.
How is clay subsidence repaired?
Most clay subsidence is repaired by dealing with the cause, confirming the building is stable, then stitching and making good the cracks. Crack stitching is a guide £80 to £180 per metre of crack inc VAT. Where foundations need strengthening, underpinning is typically £1,000 to £3,500 per metre of wall, and on deep clay mini-piling is often chosen. Prices vary by region and access and are confirmed in writing after a survey. Your engineer will confirm which repair suits the soil.
Questions about this guide
Is London Clay the worst for subsidence?
London Clay is generally regarded as the most susceptible of the UK’s shrinkable clays, and London and the South East see the highest concentration of clay-related subsidence. That reflects its high plasticity, the many older houses built on it with shallow foundations, and the number of large street and garden trees. Even so, many London homes never move.
Does clay heave cause damage too?
Yes. Heave is the opposite of shrinkage: clay takes up water and swells, lifting foundations, floors and drains. It often follows the removal of a large tree that had kept the clay dry, and it can continue for years. Heave can crack walls and lift floor slabs, so never fell a large tree near a house on clay without advice.
Can a map tell me if my house is at risk?
A map can tell you whether your area has shrinkable clay, but not what lies under your own foundations or how your house will behave. Local deposits, made ground, trees, drains and foundation depth all make a difference. Use maps as an early indicator, and rely on an engineer’s investigation if you have cracks or are planning work.