Record subsidence claims put the spotlight back on what lies beneath new builds

The hottest summer on record has left a mark that will take months to show in full. Subsidence claims at Hastings Direct reached their highest monthly level on record in August, according to Insurance Business, and insurers paid out £72 million on domestic subsidence claims in the second quarter of 2026 alone.

The longer trend is just as striking. The Association of British Insurers recorded £307 million in subsidence payouts across 2025, a record and a 10% rise on the year before. Industry commentators noted that soil moisture had not recovered from 2025 before this year’s dry spell began, which means the ground went into the summer already depleted.

The cause is well understood. Clay soils shrink as they dry and swell as they take on water. When that movement reaches the depth of a building’s foundations, the structure moves with it, and cracks appear in walls, around door frames and at junctions between old and new work. Much of the south-east of England, including large parts of Essex, sits on shrinkable clay.

Why foundation design matters more now

For existing homes, there is little to be done beyond monitoring and, where damage occurs, an insurance claim. For new builds and extensions, the design of the foundation is the main defence.

The two types most commonly used for houses and extensions are strip foundations and trench fill foundations. A strip foundation is a band of concrete laid in the bottom of a trench, with blockwork built up from it to ground level. A trench fill foundation fills most of the trench with concrete, which is quicker to build and often preferred where the trench needs to go deep.

On shrinkable clay, depth is the critical factor. Industry guidance, including the NHBC Standards used by many housebuilders, sets minimum foundation depths of between 0.75 and 1 metre depending on how shrinkable the clay is, and requires deeper foundations where trees are nearby, because roots draw moisture from the soil. Where the required depth becomes impractical, or the ground is particularly poor, piled foundations carry the load down to firmer strata.

The role of trees

Trees are often the deciding factor. A large tree can extract water from clay well below normal foundation depth, and removing a mature tree can cause the opposite problem as the ground swells back. Building close to existing trees, or to where trees have recently been felled, usually means a site-specific foundation design.

For contractors, it is a routine design question rather than an exception. L Groundworks, a Stowmarket-based contractor working across Essex and Suffolk, notes on its site that the choice between trench fill and strip foundations depends on soil conditions, the structure being built and local building regulations.

Building control and soil checks

Any new foundation is inspected by building control before concrete is poured. Where clay is suspected, a soil investigation to establish its shrinkability is a relatively small cost against the price of remedial work later.

Hastings has said it expects subsidence claim volumes to stay high through October unless sustained rain returns moisture to the ground. Whatever the weather brings this winter, the 2026 summer has given anyone planning a new build or extension a clear reason to look at what sits beneath it.