The most common cause of subsidence is the shrinkage of soils, particularly clay types, as moisture is extracted from them. This often occurs as a result of tree roots growing under the property, which becomes more likely in extended periods of hot and dry weather.  

Another common cause is drain leakage, where water escapes from underground pipes and washes away (or softens) soils so that they are no longer able to support the weight of the foundations. It can also occur as a result of a history of mining excavations beneath or around your home, so it is always worth checking for these before buying a property.