After the 2003 Heatwave: Clay Shrinkage and Subsidence

by | Aug 18, 2003 | Insurance and Reinstatement

On 10 August 2003 the temperature at Faversham in Kent reached 38.5C, the highest ever recorded in the UK. After a long, dry summer, the ground across much of London and the South East was parched. For owners of houses and low rise buildings on clay, this was the kind of weather that leads to cracks appearing, doors sticking and, in some cases, a subsidence claim.

Why clay moves

Much of London, Essex and Hertfordshire sits on shrinkable clay, of which London Clay is the best known. Clay swells when wet and shrinks as it dries. In a hot, dry summer, the ground near the surface loses moisture, and trees and large shrubs draw out even more through their roots. If the foundations of a building are shallow, as they often are in older houses, the clay beneath them can shrink enough to let part of the building drop.

Signs to look for

  • new cracks, often tapering and wider at one end, near doors and windows;
  • cracks that appear inside and outside in the same place;
  • doors and windows that start to stick or no longer close properly;
  • gaps opening up between walls and ceilings, or where an extension meets the main house;
  • cracks that change with the seasons, closing in winter and opening in summer.

What to do

  1. Do not panic. Many cracks are minor and caused by normal movement or shrinkage of plaster.
  2. Record the cracks with dated photographs and, if possible, measure their width.
  3. Note any trees or large shrubs near the building, including those in neighbouring gardens.
  4. Check your building insurance policy for subsidence cover and any excess.
  5. Do not cut down trees in a hurry. Removing a large tree on clay can cause the ground to swell, which brings its own problems, and trees may be protected.

Diagnosis before cure

Not every crack is subsidence, and not every subsidence case needs underpinning. Often the right answer is to establish the cause, deal with the vegetation and monitor the building through the seasons before deciding on repairs. A building surveyor can inspect, advise on whether to notify your insurer, and help to manage the claim and the repairs.

See our Insurance Claims and Reinstatement service, and a later subsidence claim caused by trees on clay affecting two houses.