Most residential buildings insurance policies include the 'risk' of subsidence, (normally with a minimum excess of £1,000). Damage to walls, gates, fences, car parks, pavements etc is included only if the building is also affected. Other damage caused, for example, by settlement, movement of made-up ground, demolition, construction, alteration, groundworks, excavation and landslip (resulting from coastal or river erosion) is normally excluded from a typical insurance policy. Basically, subsidence damage to a building occurs when the ground beneath its foundations fails to support its weight. The main causes of this damage are threefold: the influence of trees on clay soil, leaking drains and the result of mining activity.
The issues of leaking drains and mining activity will be explored in future editions. For now, we propose to focus on the effect of trees on clay soil. Most subsidence insurance claims arise from shrinkage of clay sub soil.
You'll be pleased to know that this is the circumstance you are most able to minimise or prevent by regular tree management. Whereas trees are everywhere, shrinkable clay soil occurs only in certain areas. So, if you do live in a clay area and there are trees in the vicinity, what are the risks?
Basically, the degree of 'risk' varies with the type, height distance and age of surrounding trees and plasticity of the clay. Cracks in buildings can be from many causes other than subsidence (such as thermal movement or lintel collapse), however a subsidence crack normally shows on the outside as well as internally, generally starting from foundation level and widening as it travels in a vertical or diagonal direction.
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