Subsidence is the downward movement of the foundations of a building due to changes in the supporting strata. It is different from settlement.
Subsidence usually happens in the following scenarios.
In most cases, the first signs of a problem are visible cracks in a particular area of the house. These may need to be measured and monitored, perhaps for as long as 12 months, or in extreme cases for longer.
Establishing whether or not there is a problem can take a long time, but there is rarely any cause for real concern unless cracks appear suddenly and are more than 3mm wide.
There could be movement in the ground beneath your home if you find:
If you spot any of these problems and can’t find a reason for them, get specialist help as soon as possible.
If it is subsidence, the sooner it is diagnosed the better. It’s important to remember that subsidence can usually be rectified. Check that your buildings insurance covers subsidence. Most insurers will aim to be as helpful as possible in dealing with any claim, and will recommend specialist advice.
Solving subsidence can be a lengthy process that can take up to two years to investigate fully and rectify.
Consumer organisation Which? estimates that about 70% of all subsidence cases are due to tree roots sucking moisture out of a shrinkable soil. Where this is the case, trees can be removed; this can be a quick and easy way to solve the problem.
Very occasionally, rather than solving the problem, removing a tree may instead add to it. An RICS member will be able to advise or put you in touch with someone who can advise you on whether a tree should be removed or simply pruned to reduce the amount of moisture it takes out of the soil.
Where the soil beneath the property is being washed away because of leaking drains or water mains, a less intrusive remedy might be possible. In most cases, repairs to leaky pipework will usually be enough to stabilise the property without underpinning.
Historic mining may result in considerable ground movement as tunnels and shafts collapse over time. This can be very difficult to fix and can lead to extensive works to stabilise the ground – or even demolition of properties. While the Coal Authority hold an extensive database of previous mining activity locations from the late 19th century onwards, there may also be very old local mining activities in some locations that have not been documented.
You can check whether a property is in a former coal mining area. If it is, you can order a mining report.
Underpinning the foundations with an engineered solution usually prevents further movement. It’s a lengthy, costly and disruptive procedure that can cost anywhere from £10,000 to £75,000 for a typical house, or even more for larger properties, depending on the extent. It can involve alternative accommodation being required during the work. It is estimated that fewer than 5% of properties suffering from subsidence need underpinning, and the Institution of Structural Engineers recommends it is only used as a last resort.
Check whether your insurance policy covers the cost of investigation and repair If the loss adjuster/insurance company considers it reasonable, you will get your costs back, minus your insurance excess. A policy excess will probably be specified in your insurance documents, commonly £1000, in which case you will need to pay up to that amount before the costs are covered by insurance.
An RICS member can deal with your insurance company and help with any claim you need to make. They can carry out the investigations, and also help design and arrange for any work needed to fix the problem. Often the insurance company will appoint their own experts, at their own cost, to investigate and design repairs and this will need to be established upfront.
These guides are for consumers based in the UK.
Published date: 14 November 2022
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