What is subsidence? | Where does subsidence occur? | How can I deal with subsidence? |Choosing a house with subsidence risks in mind | Back to subsidence 

Many factors are involved in choosing a house location such as proximity to schools, ease of commuting, the type of housing available in that area, future perceived value, cost etc. One factor usually ignored is the risk of subsidence.  Insurers categorise the country by postcode with different rates of charging for different areas, according to how they perceive the risk. Usually they perceive the risk in the cost of claims occurring in that postcode or nearby postcode.

This totally ignores the reality that the risk depends mainly on the type of soil. Heavy clays like London Clay subside due to tree roots causing shrinkage, whilst subsidence in an area of River Terraces can be caused by soil being washed away by too much water. As this material was deposited by fluvial action, it can be further moved by water. Keeping drains intact in such areas is important, whilst proximity of trees is less so.

In chalk areas, there is the risk of solution features. These are formed by gases in water dissolving the chalk to form either a hole or a putty chalk area below ground level. Piling is usually the only realistic cure.