London Clay – Got that sinking feeling?

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London Clay Sinking

London clay is disliked for building houses on, though inevitably most of Greater London is built on it. The mention of London Clay can cause home buyers’ stomachs to sink. It’s the main culprit behind subsidence, which is something any surveyor should be checking for when they survey a property.

London is a particular hotspot for subsidence. Most properties in the Greater London area are built on London Clay, which is one of the most shrinkable of soil types of all as it’s highly susceptible to changes in volume caused by high water content.

The problem:

Subsidence that causes cracking and structural damage.

Why it’s a problem:

Subsidence occurs when the ground beneath your home starts to sink, causing the property to move on its foundations. This can cause cracking and other structural damage. The three main causes of subsidence are the underlying soil, the age of the house, and the proximity of trees or shrubs.

Properties built on clay soils are vulnerable to subsidence because the soils are more likely to shrink when they are dry. Many London properties are built on London Clay, which is notorious for shrinking as it dries out. In addition, London houses built before 1965 tend to have shallow foundations and so are more prone to being affected by subsidence.

Trees planted close to properties suck moisture from the soil, especially during long spells of dry weather causing the soil to dry out which can affect the property. In contrast to this, if water continually escapes from a damaged drain or water pipe it can soften or wash away the soil beneath the foundations of a home which will also cause subsidence.

How can I tell if my house is subsiding?

There could be movement in the ground beneath your home. RICS recommend you look out for:

  • new or expanding cracks in plasterwork
  • new or expanding cracks in outside brickwork
  • doors or windows sticking for no particular reason
  • ripping 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. An RICS member 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

What we recommend:

If you’re thinking of buying a home in London that was built before 1965, definitely get a surveyor to assess for subsidence. If you already own a London property, make sure subsidence doesn’t become a problem by checking drains and pipes regularly to ensure there are no blockages or leaks. Plant new trees a good distance from the property and prune them occasionally to reduce the amount of water they take up. If you suspect there’s a problem, contact your buildings insurer and an independent building surveyor.


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