What is subsidence?

No property owner wants to hear the word ‘subsidence’. If you think your property is suffering from or at risk of subsidence, read on to find out what to look out for and what you can do.

What is subsidence in a house?

Subsidence is the name given to the shifting of the earth beneath your property. This shifting could be the settling of some of the earth underground or a vertical downwards movement. It usually happens gradually but can occur quite suddenly as well.

When the earth moves, it disrupts the foundations of your property, making them weaker, and in some cases, it undermines the whole construction of the property.

Subsidence can be caused by the ground not being properly compacted before the foundations get put down. Most commonly, it's down to invasive tree roots disturbing the earth and or drawing moisture from the soil, which dries it out and reduces its volume. When the earth gets waterlogged from leaks, it can also cause subsidence. Earth that's subject to drought for extensive periods is at risk as well, as dry soil takes up less space than wet.

Because of this drought effect, clay soil areas are more prone to subsidence because clay contains a lot of water - up to 35% of clay is water -  so when it dries out, its volume is reduced quite significantly.

Old mining areas are at risk of subsidence, so it's a good idea to have the correct searches carried out before buying a property in this kind of area.

What are the first signs of subsidence?

It's unlikely you'll feel earthmoving, but you will know there's been subsidence because diagonal cracks will start to appear in your walls, or existing settlement cracks might start to increase. These cracks may be particularly noticeable where walls join other walls or the ceiling. Around doors and windows are the most common places to find cracks due to subsidence. They can be internal and external so if you’re concerned about subsidence, check inside and outside for signs.

If doors or windows start to become hard to open and close for no reason, or you notice that your wallpaper has unexplained bumps in it, this could also be a sign of subsidence.

It’s normal for settlement cracks to appear in new build houses any time from a few months to a few years after construction. These cracks will be small vertical cracks, but if you're unsure, it's always best to consult a professional.

Find a structural engineer online.

What happens if a house has subsidence?

If a house has subsidence, the effect will depend on the severity of the subsidence. A one-time shifting of the earth that resulted in cracks that can be easily filled and painted over may not have any effect at all - although you’ll need to consider the possibility of it happening again.

But larger cracks, or seeing a drop in floor level, or visibly seeing that your house looks crooked are signs that some major subsidence is occurring and when left untreated, could leave your home unstable and unsafe to occupy. It will also reduce the property value as any buyers will want to see the issue gets fixed before purchasing, or they'll knock the cost of repairs off the price.

How expensive is it to fix?

The average cost to fix subsidence is £12,500 - this includes underpinning, which is usually only required in 10% of all cases. Underpinning is used in more serious cases of subsidence to prevent it from reoccurring. In some cases, you’ll need to move out of the property while the underpinning takes place.

Your building’s insurance may cover you for the cost to fix any damage caused by subsidence, but it won't provide cover to stop the subsidence. You'll need to check your policy carefully.

How can I fix subsidence?

Contact your insurance provider first to make them aware of the situation. They’ll be able to advise you on the next steps you should take. You'll need to identify the cause of the subsidence first, which may require a period of monitoring. After that, you'll get advice on the right solution.

For example, this could include one or more of the following:

• removing nearby trees and roots (or other invasive plant matter)
• inspecting the drainage system and or repairing leaks
• underpinning (digging out around the foundations and filling with concrete).

Read on to find out if you need a house survey if you're buying a new build property.