Subsidence: What is it, How to Spot it & Fix it.
It’s a word that no homeowner wants to hear, and it’s something you should always be on the lookout for when you’re buying a house.
Subsidence means that a house is sinking – that the ground beneath it is shifting and taking the building with it. It’s most common in detached or semi-detached houses, but can happen to any home, especially if it was built on unstable ground.
Subsidence can also be caused by extremes in weather which cause the ground to get unusually dry, or by tree roots as they push through the soil, destabilising the ground around them. Leaking drains can be an issue too, as the moisture slowly erodes the soil beneath your home.
Signs of Subsidence
Subsidence might be uncovered when a surveyor inspects a house when you’re buying it, but there are some warning signs that should set alarm bells ringing, even if you’re not an expert. Keep an eye out for:
1. Cracks both inside and out
Lots of homes have cracks; usually from when the building settled when it was first built. But cracks from settling tend to be relatively cosmetic and confined to internal walls, while cracks caused by subsidence are visible inside and out.
2. Cracks that look narrower at one end than the other
Cracks caused by settling are usually minor, whereas cracks caused by subsidence are wider at one end, as part of the wall moves away from the other.
3. Blown tiles, and cracks around doors and windows
As the ground moves and walls contort, tiles adhesive can crack and fail, and walls can separate from openings like doors and windows.
4. Doors and windows won’t close properly, or stick when you try to open them
Subsidence can cause door and window frames to twist and shift, which means doors and windows might get stuck shut, or you might have trouble getting them to close. Of course, a jammed door on an old property may just have rusted hinges, or have been painted shut. But it should ring alarm bells all the same.
5. Wallpaper that’s wrinkled at wall or ceiling joints
As walls shift, wallpaper wrinkles and tears, usually at the point where walls and ceilings join.
What houses are at risk of subsidence?
Houses built on clay soil are more likely to experiencing subsidence; Clay soil can shrink, crack, and shift during hot, dry weather – making the ground unstable and possibly causing the foundations of your property to sink.
Properties in London, most of which are built on London Clay, are at greater risk of developing subsidence. London Clay is one of the most shrinkable of soil types, and is highly susceptible to changes in volume depending on its water content. In fact, the capital city has one of the highest shrink-swell hazards in the country.
While property type doesn’t normally influence the risk of subsidence, a lot of houses built in the Victorian and Edwardian era have shallow foundations – shallower than the UK’s current minimum of a metre – which can make them more susceptible to damage from movements in the ground.
How to prevent subsidence
Trees and shrubbery around your property can increase the risk of subsidence, as they absorb water which can make the soil much drier. So if you’re making improvements to your garden, be sure to plant at least five meters away from your property, and prune branches on your trees regularly.
You should also make sure you’re keeping your pipes and drainage systems well maintained to stop water leaking into the soil underneath your house.
What can I do if my house is subsiding?
Subsidence is serious, but it is fixable and can usually be remedied without knocking down walls or digging up floors.
Before you do anything, check if you’re covered for subsidence on your Buildings Insurance, as your insurer should be able to advise on what you need to do. In some cases, a surveyor might just keep an eye on your home to make sure it’s not getting worse. If nothing changes over time, you might just need to repair the cracks with metal fixings and fillers.
If cracks are getting worse, your surveyor might want to take soil samples or take a closer look at the foundations to find out why. And if the house continues to move, you might need to underpin your home – that means adding a new layer of solid foundations below the ground.
In the worst – but very rare – cases, you may need to rebuild areas of your home, though this level of action is unusual.
If you do need to take action, it can be pricey (underpinning starts at around £10,000), so make sure you get all the right checks when you’re buying your home, and that you’re covered for all eventualities when you take out insurance.
What is heave?
Heave is the opposite of subsidence.
Instead of the ground beneath your home shrinking, heave happens when the ground swells. This happens when the ground around your home floods from the inside out, forcing your home up and out of the ground. You should be on the lookout for the same issues when viewing a property.
Trees, and established trees in particular, remove water from the ground around your home. Over time, the local water table can come to rely on these trees to maintain its delicate balance. If trees are suddenly removed, this outlet for water is taken away. So you may want to be wary of new developments on land previously covered in trees.
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