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Subsidence

Subsidence is the downward movement of the ground that supports the building.  It can cause structural damage to the building so it is important to keep an eye out for it, so that you can remedy it before expensive repairs are required.  We’ve put together what you need to know.

What Causes Subsidence?

Subsidence usually occurs when homes are built on clay soils, and either the water table drops due to a prolonged dry spell, or water is sucked out of the soil by the surrounding trees and plant life.  When the clay contracts due to the lack of water, it pulls on the foundations, which may cause structural damage to the home.  Another form of subsidence occurs when water leaks into the soil from something such as a broken pipe or leaking drain, thus washing the soil away from the foundations.  This happens to soil that has a high sand or gravel content.

Identifying Subsidence

Subsidence could be occurring in your home if you find one or more of the following:

• new or growing cracks in plasterwork
  
• new or growing cracks in exterior brickwork
  
• doors and windows that are hard to open or are sticking for no reason
  
• rippling wallpaper that isn’t caused by dampness

While cracking is the most obvious sign of subsidence, seeing a crack does not necessarily mean that there is a problem.  This is because most buildings will experience cracking at some stage, especially new home and new extensions or additions.  These are still settling under their own weight.  The cracks that you should be concerned with are those that appear suddenly, especially a prolonged bout of dry weather.  These cracks are usually wider than 3mm and are normally wider at the top than they are at the bottom.

A surveyor will be able to tell you if there is subsidence in your home or not, and what is causing it.  If they cannot give you a proper diagnosis, they will recommend that you engage the services of a structural engineer. Specialist geological and drain surveys may also be required as the movement of soil can sometimes crack drains or water mains.

Rectifying Subsidence

If subsidence is occurring on your property, there is no need to worry as it is a problem that can be fixed.  Also remember that subsidence is usually covered by your building insurance.  Here are some of the most common methods for rectifying subsidence:

• Underpinning the foundations – doing this will usually stop the foundations from moving any more, however it is a lengthy and costly process.  It is usually a last resort, and only 20 to 30 percent of homes that suffer from subsidence will need underpinning.
  
• Remove tree roots/Prune trees – many cases of subsidence are caused by nearby tree roots sucking the moisture from the soil, causing it to contract.  If this is the case, the tree can be removed, or pruned so that it does not demand as much moisture.  You will need to talk to an arborist and a surveyor to find out the best cause of action to take in this regard.
  
• Repairing Pipework – if the subsidence is occurring due to the soil being washed away by leaking pipes or drains, the solution can be as simple as repairing the leaks or replacing the pipes.
  

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