RICS property guides

Guide to subsidence

February 2008

What is subsidence and how is it caused?

Subsidence usually happens where:

• Previous mining activity has taken place
• Some houses are built on clay soils, and either the water table drops due to a long, dry spell or water is sucked out of the soil
• By trees and bushes. As the clay contracts it pulls the foundations, triggering deflection which may cause structural damage to buildings. Different types of clay shrink and swell at different rates
• Water leaks into the soil from, for example, a broken drainpipe and washes soil away from the foundations. This happens to soils with a high sand or gravel content usually, or sometimes in chalk.

How can I tell if my house is subsiding?

There could be movement in the ground beneath your home if you find:

• New or expanding cracks in plasterwork
• New or expanding cracks in outside brickwork
• Doors or windows sticking for no particular reason
• Rippling wallpaper that isn’t caused by damp.

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. They will recommend specialist advice.

A chartered surveyor will be able to work out whether or not there is subsidence and what the likely cause is. You may also need specialist geological and drain surveys. Moving soil can sometimes crack drains or water mains.

How long will it take to rectify?

Establishing whether or not there is a problem can take a long time. There is rarely any cause for real concern unless cracks appear suddenly and are more than 3mm wide.

In most cases the first signs of a problem are visible cracks in a particular area of the house and these may need to be measured and monitored, perhaps for as long as 12 months. Solving subsidence can be a lengthy process which can take up to two years.

How to fix it

Underpinning

Underpinning the foundations usually prevents further movement. It’s a lengthy, costly and disruptive procedure that can cost anywhere between £5,000 and £50,000 or more. It is estimated that less than 10% of properties suffering from subsidence need underpinning and the Institution of Structural Engineers recommends it is only used as a last resort.

Tree roots

Consumer champion Which? estimates that about 70% of all subsidence cases are due to tree roots sucking moisture out of the soil. Where this is the case, trees may be removed. It may be a quick and easy way to solve the problem.

More importantly, instead of solving the problem, removing a tree may add to it but this is usually very rare. Your chartered surveyor will be able to put you in touch with someone who can advise you on whether or not a tree should be removed or simply pruned to reduce the amount of moisture it takes out of the soil.

Pipework

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 be enough to stabilise the property without underpinning.

Who pays?

Check whether your insurance policy covers the cost of investigation and repair.

If the loss adjuster/insurance company considers this reasonable, you will get your costs back.

A policy excess will probably be specified in your insurance documents, in which case you will need to pay up to that amount before the costs are covered by insurance. Your chartered surveyor will deal with your insurance company and help with any claim you need to make. They can also help design and arrange for any work needed to fix the problem.

RICS (Royal Institution of Chartered Surveyors) is the largest organisation for professionals in property, land, construction and related environmental issues worldwide. We promote best practice, regulation and consumer protection to business and the public. With 120 000 members, RICS is the leading source of property related knowledge, providing independent, impartial advice to governments and global organisations.