A property owners' guide to subsidence

What is subsidence?

Subsidence happens when the land beneath a property starts to sink, leaving the walls and foundations destabilised. It can be caused by a number of reasons, so bear in mind that properties exposed to the following factors are at greater risk of being affected.

Some of the most common reasons for subsidence include:

Soil type

Certain soil types, such as clay, are particularly prone to shrinking and cracking when dry. They can also swell and expand when wet. This movement creates instability and can lead to subsidence.

Tree roots

Thirsty trees (in particular willow and oak trees) draw water from the soil, causing the ground to dry out, crack, and then drop. In particularly dry weather roots can also spread to find new water sources, exacerbating the issue.

Mining

Areas that have been excavated and then refilled, such as old quarry or mining pits can be unstable as the ground shifts.

Construction and drainage

Buildings with shallow foundations are at greater risk of subsidence, as are properties where drainage is a problem. For example, prolonged leaks from drain pipes can soften or wash away soil, leaving foundations unstable. 

Is subsidence the same as heave and settlement?

Subsidence isn’t quite the same as heave and settlement although they both affect the structure of buildings:

What is settlement?

Settlement is similar to subsidence in the sense that the building is sinking. However, instead of it being caused by factors impacting the ground (such as soil type or leaks), the instability is caused by the weight of the building itself. In new buildings it is normal for settlement to occur to some extent for the first few years after it has been built.

What is heave?

Heave is the opposite of subsidence. Instead of sinking, buildings are pushed upwards, often because the soil has expanded. This typically happens when the soil becomes wet and saturated. This could be down to weather or because something has led to a localised increase in water – for example, if a tree has been removed which means water is not absorbed by its roots. 

How can I check for signs of subsidence?

Subsidence is associated with cracks in walls, but not every crack is a sign of subsidence. Nevertheless, there are some tell-tale signs that could indicate subsidence, including:

• diagonal cracks that are bigger at the top and wider than a 10p piece;

• cracks that can be seen inside and outside of the building;

• cracks close to doors and windows or in the joins between an extension and the rest of the building;

• uneven or sloping floors with gaps around skirting boards;

• doors and windows that are difficult to open because frames have warped or dropped.

Can subsidence be picked up in a survey?

Subsidence will usually only be picked up by a full structural (buildings) survey. If you’ve got any concerns about subsidence, it’s worth making the investment and having this checked. A valuation survey (usually carried out by the mortgage lender) is unlikely to spot signs of subsidence.

Can a builder diagnose subsidence?

An experienced builder may be able to detect signs of subsidence, but you’ll need a chartered surveyor or structural engineer to carry out a formal survey and provide a full report of their findings. It can take up to 12 months for a full report to be provided if the surveyor determines that your property needs to be monitored before they can decide whether subsidence is occurring. 

How can I prevent subsidence?

Realistically, there are some factors that you won’t be able to control, for example if your home is built on clay or near a former quarry or mine. However, you can minimise the risk of subsidence by:

• ensuring large, particularly thirsty trees are planted further away from the house, it’s recommended that mature willow trees be planted 40 m away from the house;

• cutting back any large trees if they’re already on your property;

• reducing the risk of waterlogged soil by making sure gutters and pipes are maintained and don’t leak, you can also collect rain in water butts.

What happens if your property has subsidence?

If you suspect your home has subsidence, it’s crucial to have an expert assess the situation; this is something your insurer will be able to help with. They will then be able to offer advice and put a plan in place to rectify and prevent the problem from happening again.

How can I rectify subsidence?

If there is a clear problem, such as trees or damaged pipes under the house, the solution should be relatively simple. In these scenarios, a surveyor or engineer is likely to recommend cutting back trees or removing them altogether in addition to fixing pipework.

If the subsidence is serious, your home may need to be underpinned. This essentially means the soil underneath your home will be replaced with materials that won’t erode – giving your property a solid foundation. Most homes won’t need such extreme work carried out and underpinning is normally seen as a last resort.

What happens if I ignore subsidence?

Subsidence is something you really shouldn’t ignore and the consequences if you do can be severe.

Initially, there may only be cracks but if not dealt with they can worsen, which can affect the value of your home. Doors and windows can become difficult to open and gaps can start to appear near skirting boards and extensions. While you might get used to these inconveniences, it can become a health and safety issue in the long term. Not to mention, it is likely to affect the value of your home, which could be an issue if you want to sell. Many mortgage providers won’t lend on a home that has known unresolved subsidence issues.

Needless to say, the real risk is that over time your home becomes completely structurally unsound, and safety becomes a real concern.

As overwhelming as a diagnosis of subsidence might be, it’s far better to deal with the issues as soon as you can. Putting it off could mean having to deal with a bigger, more expensive problem later on.

How long does subsidence last?

The time needed to resolve the issue will depend on how badly affected your home is. For some properties, subsidence can be rectified in days or weeks, but some could take up to two years depending on the works required. 

What should I do if I’m buying or selling a house with subsidence?

If you’re selling a house and you know it has a history of subsidence, you should always disclose it. In most cases, the buyer’s solicitor will ask about subsidence and it will be highlighted by a buildings survey, so it’s better to be upfront in the first place, especially if you’ve resolved any issues.

If you’re buying a home and are concerned about subsidence or have been told about a history of subsidence, it’s a good idea to arrange a full structural survey for your peace of mind.

If the house has been underpinned, it should also come with a completion certificate that shows remedial work has been carried out and completed. Any work carried out under the guidance of an insurance provider should also come with a certificate of structural adequacy.

It’s also worth asking your solicitor to find out how much the current owner pays for home insurance. You can then compare quotes and costs yourself to get an idea of what your options are and what’s available. Some mainstream insurers are wary of homes with histories of subsidence so you could find your choice of providers limited, although an insurance broker should be able to help you with this. 

Can I rent a property with subsidence?

If you’re a landlord, it’s your responsibility to ensure the property you rent is safe and habitable. It doesn’t matter whether you rent out domestic or commercial property, if you suspect subsidence, you should take steps to resolve the problem as soon as possible. Remember – cracks aren’t always a sign of subsidence and it could be nothing more than wear and tear. 

Does insurance cover subsidence?

If there’s no previous history of subsidence, either at the property or in the local area, your home buildings insurance (or landlord buildings insurance) will provide cover. Because of the serious nature of subsidence, you can expect the excess to be high – often around the £1,000 mark.

If your home is in a high-risk area for subsidence, but hasn’t actually suffered from it, insurers may charge you a higher premium to reflect the increased risk. Some insurers might refuse to provide cover altogether or exclude subsidence in the policy.

If your home suffers from subsidence whilst it’s insured, your insurer will usually increase your premium and excess to reflect the increased risk.

How many years does subsidence affect insurance?

This really depends on the insurer, but subsidence is something you’ll always be expected to declare. If you switch to a new insurer, they could also ask for an up-to-date structural engineer’s report before agreeing to provide cover. In some extreme cases, you might find it difficult to find another insurer who is willing to take on the risk and you may have to stick with your existing insurer.

If the subsidence happened sometime in the past (usually ten years or more), you may not need an engineer’s report, depending on the insurer.

Dealing with subsidence

If you think your home has subsidence, it’s more cost effective to deal with it right away. You can either arrange for a structural engineer or surveyor to assess the house first or you can speak to your insurer who can organise this on your behalf. It’s only after your home has been structurally assessed that a solution can be found.