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

Insurers define subsidence in words such as "downward movement on which the structure stands". When filing an insurance claim for subsidence it is important to bear this in mind. One has to make the distinction between subsidence and settlement. Settlement occurs when the soil is compressed by additional weight such as the construction of a new house. One tries to design foundations to keep the pressure on the soil fairly uniform, so that settlement, which is fairly inevitable, is uniform and the house owner doesn't know it is occurring.

If settlement is not uniform however, there may be cracking. However, if settlement does occur, it happens more rapidly shortly after the structure has been built and is usually therefore covered by any NHBC warranty. However, one must be careful when building a new extension. The old part of the house has undergone whatever settlement it is going to undergo but the new part will inevitably undergo some settlement of its own unless built on rock. The designer should ensure that the pressure on the foundations of a new extension is controlled to minimise this effect. Moreover the joint with the original house should be carefully designed with the possibility of settlement in mind.

Piled foundations significantly reduce settlement but usually cost more. However, if the only way of removing excavated soil arising from dug foundations is to carry it through your house, then piling may be a better solution on both scores as no or only a little excavation is then required.