Subsidence: causes, symptoms and cures
Subsidence can be anything from just creating some undesirable cracks, to needing serious and expensive structural work.
If your home suffers from subsidence, you could find yourself facing a costly repair bill. Understand the causes with our simple guide.
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What is subsidence and what causes it?
Subsidence is the slow sinking of your home’s foundations, which is most often caused by:
Nearby trees and shrubs sucking up the moisture in the soil beneath your home.
Leaking drains softening the ground beneath your house.
Your house being built over an old mine, which could be structurally unsound.
Clay soil is particularly vulnerable to subsidence, as it is sensitive to moisture. This makes it expand when wet and contract when dry – not ideal with unpredictable British weather.
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How does it happen?
Subsidence is more common in Victorian and Edwardian houses as their foundations are shallower than the current UK minimum (1 metre). As such, they’re more at risk of damage.
It's normally the result of a three-step process:
1. Trees and shrubbery around your home suck up moisture from clay-rich soil.
2. A 'shrink-swell' effect causes the clay to harden and crack as it dries.
3. Cracked soil causes sinking in the foundation of your home.
Subsidence is also more common in areas with clay-rich soil, like much of south-east Britain. The Subsidence Support website has a useful map of areas at risk of subsidence.
What are the signs of subsidence?
Your home might be suffering from subsidence if you spot:
Sudden cracks in plaster and brickwork that are wider at the top than the bottom.
Doors and windows sticking for no apparent reason.
Rippling wallpaper that isn’t caused by damp.
Cracks can also appear in fairly new houses due to ‘settlement’. This is common in newly-built houses and doesn’t indicate any risk of subsidence.
The main difference is that settlement cracks generally don’t get wider with time, nor are they bigger on one side than the other.
In either case, if you spot any of these problems it’s worth getting in touch with your home insurer. Plus you could have a qualified surveyor look at the problem to limit the damage.
Heave is a separate problem which is often covered under the same insurance guidelines as subsidence.
Heave has the opposite effect to subsidence. It happens when the ground beneath a building becomes saturated with water and begins to swell, moving upwards and often sideways.
This can have similar symptoms, and cause similar damage to subsidence.
How can you prevent it?
There are a few steps you can take to minimise the risk of and damage caused by subsidence:
Make sure that trees and shrubs are planted at least 5-10 metres from your house.
Regularly prune the branches on your trees and remove any that are too close.
Keep pipes and drainage systems well maintained, to prevent water leaking into the soil beneath your house.
Check the surveyor’s report for signs of subsidence before buying any new house.
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How can you fix it?
The most common fix for subsidence is underpinning your foundations.
This involves installing support beams, or a second concrete layer, to strengthen your foundations.
Most insurance companies offer cover for subsidence-related damage, though the scale of the repairs can often leave you facing a large excess, often £1,000.
Having an underpinned home can often be an indicator to insurers that your home is at risk of subsidence again, which may lead to higher prices.
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