In July 2022 temperatures in England passed 40 degrees for the first time on record. After a dry spring, clay soils across London and the south east shrank, and cracks were starting to open in houses that had stood untroubled for decades. After the last comparable summer, in 2018, insurers saw a sharp rise in subsidence claims, and the same was expected in 2022.
Is it subsidence?
Not every crack is subsidence. Plaster shrinkage, thermal movement and old settlement are common and usually harmless. Subsidence is downward movement of the ground beneath the foundations. On shrinkable clay, the usual cause is moisture being drawn out of the soil, by dry weather and by trees and shrubs nearby. Cracks that open in summer and close in winter, are wider at the top, and run diagonally near doors and windows are typical signs.
Proving the cause
In a subsidence claim, the diagnosis is the claim. Until the cause is proven, nobody can say what the repair is, what it costs, or whether it will hold. A proper investigation usually brings together:
- trial pits to expose the foundations and the soil;
- laboratory tests on the clay for shrinkage and desiccation;
- identification of roots recovered from the pits;
- an arboricultural report on nearby trees;
- level monitoring over time, to show movement through the seasons.
The right repair
Once the cause is proven and dealt with, often by removing or managing the vegetation, many houses need only crack repair and redecoration rather than underpinning. Spending on the investigation first avoids paying for the wrong repair. Investigation and reporting follow the RICS guidance note Surveying assets in the built environment.
See our Insurance Claims and Reinstatement service, and how subsidence was proved and then repaired at two neighbouring houses.