What is subsidence?

Subsidence has the potential to be quite a serious issue for homeowners, as it can make your house unsafe, lead to expensive damage costs, or even devalue your house. We’re not here to scare you though, we’re here to give you the facts.

Knowing what subsidence is, how to spot it, and what you can do to fix it will make you feel safer in your home. It might also help you to spot any subsidence early before it does any real damage.

What is subsidence?

Subsidence is a type of structural movement, meaning that it can affect the core structure of your house and its foundations. There are a few other types of structural movement, but we’ll get to them shortly. Subsidence specifically means that the ground underneath your house is sinking. This can unbalance your foundations, which in turn might move the walls and floors off their groundwork and destabilise your house. It’s most noticeable by big cracks in your walls, both inside and out. We’ll go through the easiest ways to spot subsidence just a bit later.

What causes subsidence?

So what actually causes subsidence? There is a range of factors in play, but generally subsidence is caused by issues in the ground around and underneath your property. Here are a few of the main things that can cause subsidence:

• Trees and shrubs - Roots from trees and shrubs can grow into the foundations and make them unstable. It’s not always the case though, not every tree growing next to a house will cause subsidence.
• Soil type - Areas where the ground is prone to drought, and clay soil areas tend to become water-logged in wet weather then crack and move in dry weather. This kind of constant change has the potential to cause subsidence.
• Local mining activity - Houses built on old quarry fill-ins or over old mines can be unstable if tunnels collapse underground.
• Nearby drains - Leaky drains can wash away soil and destabilise the ground around your foundations
  

You can find out more about the causes of subsidence in this handy guide. If you’re planning to have any work done near your drains, you might want to read our blog ‘What is a Build Over Agreement?’.

Is structural movement the same as subsidence?

Subsidence is a type of structural movement, but it’s not the only kind. It’s a good idea to know the differences between the types of structural movement so that you can keep an eye out for cracks that might be a sign of a big problem.

These are the main types of serious structural movements:

• Subsidence - We’ve gone over this one, but just to be sure, subsidence means the ground underneath your house is sinking and destabilising your foundations.
• Heave - Heave is when the ground underneath a property moves upwards, usually from soil expanding when it’s wet or frozen. It can destabilise your house in the same way that subsidence can.
• Landslip - Landslip is when the ground underneath a house (usually one built on a slope) falls away and the house starts to slide sideways.

There are some types of structural movement that might cause small cracks in your walls but you might not need to worry about so much. Here are a few examples:

• Settlement - Settlement happens when the weight of a building squashes it into the ground. Most houses will naturally sink a tiny bit after being built, but when a building settles unevenly the foundations can become damaged.
• Sway - If a building faces extreme winds or even an earthquake, it will sway. Houses that aren’t resilient to sway might see some destabilisation issues if they’re in areas with regular storms or earthquakes (you probably don’t need to worry about earthquakes in the UK).
• Roof spread - If a roof or the walls connected to it aren’t built properly, the weight of the roof can push the walls apart and create cracks where the roof meets the supporting walls.

How to spot subsidence

There are a few key things to look out for when trying to spot subsidence. There are a few common indicators, like cracks, that can show early signs of subsidence, but not every crack means that your house is subsiding. A new build or a new extension might see small cracks as the building settles, and some cracks are caused by natural temperature shifts making the bricks expand and contract.

A good way to tell if a crack is a sign of subsidence is to ask yourself these questions:

• Is the crack more than 3mm thick (could you fit a 10p coin in the crack)?
• Is the crack diagonal, wide at the top and thin at the bottom?
• Can you see the crack inside and outside the house?
• Can you see the crack near doors and windows?
• Is the crack spreading under the damp-proof course (the layer of waterproof materials near the bottom of a wall that prevents rising damp).
• Did the crack appear suddenly, maybe after a long period of dry weather?

If you answered yes to most of those questions, it’s possible that you have some subsidence, so it might be a good idea to talk to an expert as soon as you can.

You might not always see a crack right away, but it might be worth looking for one if you start to notice any of these things happening:

• Wallpaper creasing at the joins where the wall meets the ceiling
• Doors and windows not opening or closing properly
• Cracks where an extension meets the original house

If you see cracks in your house, you might be wondering who’s paying the building's insurance. It’s worth checking out our blog ‘Who pays Buildings Insurance?’

Does subsidence stop on its own?

Some subsidence may stop on its own after a single shift. Other subsidence can be ongoing and might continue to destabilise your foundations and cause damage to the rest of your house. There isn’t a rule that one cause of subsidence will cause more damage than another, so it can be a good idea to talk to an expert and get an inspection as soon as you can. A subsidence survey could cost you between £600 and £1750 but, if you think you have a problem, it can be much better to get it checked early.

How to fix subsidence

Generally, it’s a pretty good idea to talk to your insurance company if you think you have some subsidence. Fixing subsidence has the potential to be quite an expensive process, and how it is done tends to depend on a few factors. Building insurance tends to cover the costs of fixing the damage caused by subsidence, but it might not cover the cost of fixing the cause of the subsidence itself.

If you’re wondering how subsidence might affect your building insurance, you can check out our blog ‘Subsidence and Home Insurance’

The main ways that subsidence can be fixed are:

• Underpinning - If your foundations have been damaged, underpinning deepens and strengthens the existing foundations.
• Removing trees - Cutting down trees and shrubs that are growing into your foundations can help to stop them from causing any more damage.
• Updating pipes - Replacing pipes that are causing water damage to your foundations helps to make sure they don’t cause more.

How much does subsidence devalue a property?

Subsidence can devalue a property if left untreated, as it is fairly unlikely that anyone will want to pay full price for a house that is subsiding, due to the potential for future repair costs. It is generally expected that untreated subsidence can devalue a property by around 20%. Very serious cases of subsidence, if left untreated, could devalue a property by much more. It might be worth getting any subsidence issues fixed before trying to sell your house to avoid any potential devaluation.

A few final tips…

Here are a few last things to remember about subsidence:

• Subsidence is not the only type of structural movement, but it can be one of the more serious ones if left untreated.
• If you spot a crack in your wall that can easily fit a 10p coin, it might be a sign of subsidence.
• Leaving subsidence untreated could devalue a property by 20% or more.

Urban Jungle is not a financial advisor and information in this article should not be taken as advice or recommendation.