Clay Sub-soil in the Greater London Area
- April 2, 2015
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London and the surrounding areas including most of the South East of England is built on shrinkable clay sub-soil. This type of soil is prone to movement particularly in the colder winter months when wet ground causes the clay sub-soil to become loose, this leaves properties that have been built without the correct foundations at risk of movement. This can also become a problem in the summer months when the ground becomes particularly hard and cracks.
The depth and quality of foundations (namely houses built with foundations less than two metres deep) along with the proximity of trees, vegetation and drainage systems will all contribute toward the possibility of subsidence in your property. Perhaps most surprisingly, the growth of vegetation has the most significant impact upon the swelling and shrinkage of sub-soil, bushes and shrubs that lay mostly inactive in the winter months suddenly spring into action and begin to bloom as we enter the spring and summer time.
1 in 50 homes built in the Greater London area and the South East of England has at some point in its life span been affected by subsidence. Over the last 10 years the effects of subsidence have cost the economy an estimated £3 Billion pounds and recent research in Europe predicts a further 50% rise in claims for subsidence in the next 25 years.
Fortunately, there are a few things that you can do as a homeowner in order to reduce the possibility of subsidence. Keeping trees and shrubs trimmed and in good order can have a positive effect. In some extreme cases you may need to have your property underpinned which is essentially the process of having the foundation of your property deepened. This is a lengthy and costly process and is estimated by the RICS (Royal Institute of Chartered Surveyors) to cost anywhere between £5,000 and £50,000 and possible even more.
It is therefore, recommended that you protect yourself against this amongst other things when purchasing a property by instructing a Surveyor to carry out an inspection of the property. Your surveyor will not be able to tell you from a single inspection whether or not the any movement is long standing and non-progressive, however, they will be able to look for the tell-tale signs and if they believe the property to be at risk they will advise you to instruct a structural engineer who will then be able to carry out an inspection using varying equipment to monitor the movement of the property over a longer period of time.