What is subsidence and how is it caused?
Subsidence usually happens when: Houses are built on clay soils, and either the water table drops due to a long, dry spell or water is sucked out of the soil by trees and bushes. As the clay contracts it pulls the foundations, triggering deflection which may cause structural damage to buildings. Different types of clay shrink and swell at different rates. Water leaks into the soil from, for example, a broken drainpipe and washes soil away from the foundations. This type of subsidence happens to soils with a high sand or gravel content.
