Subsidence: What is it and how to prevent it

Subsidence is a word dreaded by home owners and buyers alike. We look at what subsidence is, how to avoid it, how to fix it - and the implications it may have for the future sale of your home.

Angela Kerr Director, Editor

What is subsidence?

Subsidence is when the ground beneath a property sinks, pulling the building’s foundations down with it. Subsidence usually happens when the ground loses moisture and shrinks due to long periods of dry weather or because of trees and shrubs. However, activities like mining nearby and poor ground works can also lead to subsidence. Subsidence can lead to significant structural damage in buildings.

Historic movement vs active movement

There are two main categories with subsidence:

1. Historic movement – which has caused problems in the past but stopped or been repaired
2. Active movement – which is currently causing problems.

As you’d expect, historic subsidence is usually less of an issue, however it can still affect your house price when it comes to sell. While active subsidence will cause problems and inevitably reduce the worth of your home.

Heave

Subsidence is not the same as heave, which is where parts of the ground under your home shift upwards pushing the foundations higher. It is also different to landslip or landslide, where the ground your home was built on moves down a slope or is washed away.

Settlement

It is also worth noting the difference between subsidence and settlement. According to the Financial Ombudsman Service, subsidence is caused by the ‘downward movement of the site on which a building stands – where the soil beneath the building’s foundations is unstable’. Whereas settlement is “downward movement as a result of the soil being compressed by the weight of the building within ten years of construction”. It is important to know the difference as most home insurance doesn’t cover settlement.

House subsidence risks: What are they?

The main risk factors that increase the chances of subsidence:

• Trees – If you have trees or large shrubs planted too close to your home they can cause subsidence as the plant drains the moisture from the soil causing it to dry out and sink. Estimates suggest that around 70% of all subsidence cases are a result of tree roots absorbing all the moisture out of soil.
• Clay – This type of soil changes a great deal with the weather. When it is hot and dry it can shrink, crack and shift which makes the ground unstable and there is a greater risk of it sinking.
• Drought – If you live somewhere that is prone to a drought then the soil could dry out which increases the chance of subsidence.
• Leaks – A leaking drain or water main can soften the soil, or wash it away, causing sinkage.
• Age and construction – If you live in a period property there may be a greater risk of subsidence as your house may have shallower foundations than a more recently-built home. However, the flipside of this is that older properties tend to be built from bricks and lime mortar which could make them more flexible and less likely to be damaged by the ground shifting beneath them.
• Mining – This is one of the more well-known causes of subsidence. If your house has been built near to a former quarry or pit, then it could be unstable as the material used to fill the site will shift as it decomposes. Your house could also be affected if mining activity occurs close by. You can purchase a subsidence claims report from the Coal Authority to see if your property is affected.
• Poor groundworks. If the foundations aren’t done correctly before building, this can lead to subsidence problems.

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What are the signs of subsidence?

The main signs of subsidence to look out for are:

• Cracks in walls or ceilings
• Doors or windows sticking
• Uneven floor surfaces
• Wallpaper crinkling at wall/ceiling joins
• Expansion of existing cracks
• External wall cracks appearing or expanding

Cracks in walls or ceilings

Subsidence cracks have a number of characteristics:

• Size: Subsidence cracks are usually wider than 3mm (the width of a 10p coin). And also wider at the top than at the base.
• Shape: Subsidence cracks caused by subsidence are normally diagonal.
• Location: Subsidence cracks usually appear close to doorways and windows.

Doors or windows sticking

You should also look out for doors and windows that stick as this could be caused by the frames warping as part of your house sinks.

Uneven floor surfaces

Another sign to watch out for is sloping or sinking floors. You may spot gaps near the skirting board or the floor may appear uneven.

Wallpaper crinkling at wall/ceiling joins

Keep an eye on wallpapered rooms for signs of rippling at the wall and ceiling joints. You may also spot cracks where an extension has been joined to your main home.

Expansion of existing cracks

If the crack gets bigger than 2mm or you notice other signs of subsidence, such as doors or windows sticking, you should get a professional in to take a look.

External wall cracks appearing or expanding

Subsidence cracks are typically visible on both the outside and the inside of your home.

Are all cracks in my house signs of subsidence?

No. One crack in a wall is not a sure sign of subsidence. It is far more likely that the crack is a result of the walls or ceilings of your home swelling and shrinking over time due to temperature changes. Also, a new home – or one that has had some major plastering – may develop some cracks as the plaster dries out or the structure settles onto its foundations.

Also, supporting lintels over doors and windows can fail causing diagonal cracks similar to building subsidence. And if an extension or conservatory isn’t properly connected to the main building, cracking can occur between the two.

Signs of subsidence inside your house

As we explain above, you should look out for subsidence cracks in your walls, doors and windows sticking and wallpaper creasing.

How to fix subsidence

The big question now is how to fix subsidence. If you think you may have subsidence, the first step is to contact your buildings insurer. The sooner it is picked up the easier it will be to deal with. The insurance company will arrange for a structural engineer to inspect your home and confirm if it is in fact subsidence. It may be that the engineer decides your home needs to be monitored before they can determine whether the ground is sinking. This can take up to 12 months.

If the problem is being caused by tree roots then the easiest solution is to remove the tree, but you should only do so after discussing with your structural engineer and with the help of a tree surgeon. If you get it wrong, you could make the situation worse and cause more instability.

Similarly, if leaky pipework is the cause, get this fixed and see whether that helps the property to stabilise before looking at other options.

However, the concern with telling your insurance firm straight away is that it could mean your insurance premiums rise, even if it turns out you don’t have subsidence. All insurers view risks differently so, you might want to consider getting a structural engineer to undertake a subsidence survey first to confirm you have subsidence before you involve your insurer.

What is a subsidence survey?

If you want to find out for certain if you have building subsidence before speaking to your insurer, then you’ll need a subsidence survey by a structural engineer. This will involved them investigating the existence and extent of subsidence. The subsidence survey will begin with a visual inspection to look at cracks in the walls and other obvious signs of subsidence.

They’ll be able to determine whether these are signs of a serious problem or just as a result of normal movement. But it may not be obvious straight away and may need to be monitored over time. Plus, you may need geographical and drain surveys to be carried out, to determine whether issues such as unstable soil or a broken drain could be causing subsidence.

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Underpinning a house explained

In the worst cases of subsidence, your house may need to be underpinned. This can be expensive and disruptive with costs reaching £50,000 in some cases. The good news is the Royal Institution of Chartered Surveyors (RICS) estimate that less than 10% of properties that are affected by subsidence need underpinning. It is only used as a last resort. Claims data from the Association of British Insurers suggests that in most cases the cost of dealing with subsidence is much lower as the average payout is £6,250.

Resin repairs: A cheaper fix?

This is a new technique that can replace the need for underpinning; the process involves injecting resin into the ground around the building. This hardens like concrete in as little as 15 minutes. It’s much less disruptive than underpinning however your structural engineer and insurer will explain which is the right solution for your home.

Fixing the cosmetic damage

Once your subsidence problem has been fixed, you’ll want to get any cosmetic damage repaired. For example, this may include plastering over subsidence cracks and replacing wallpaper.

Does subsidence stop on its own?

Whether or not subsidence stops on its own depends on the cause. If the cause is a one-off event, such as a burst water main, then subsidence may stop on its own once the event is fixed. However, if the cause is ongoing, such as soil erosion or mining activity, then subsidence is likely to continue, and you should address the issue as soon as possible.

Subsidence insurance: Am I covered?

Your buildings insurance policy will usually cover you for damage caused to the structure of your home by subsidence, although according to the ABI, most policies will have an excess of around £1,000 for a subsidence claim. And damage to surrounding structures such as garden walls, fences, gates, patios and driveways isn’t usually covered, unless the damage happens at the same time as the damage to your home. 

If your home is so severely damaged that you can’t live in it, your insurance should cover the cost of alternative accommodation while repairs are being carried out. But you should contact your buildings insurance provider to find out exactly what is covered under your policy and how much excess you will need to pay. 

Claiming for subsidence caused by coal mining 

However, if you’re claiming for damage caused by coal mining, these are dealt with through the Coal Authority, not through your usual home insurance provider. 

You’ll need to:

• Download and fill out the Coal Authority’s Damage Notice Form 
• Send your completed to the owner of the coal mine in your area 
• The coal mine owner will usually send an engineer to inspect your home’s damage 
• You’ll also need to tell your home insurer you’ve made a claim for subsidence through the Coal Authority 

How to prevent subsidence

If you live in a house that is at risk of subsidence, then there are a couple of steps you can take to reduce the chances of your property sinking.

Firstly, keep the trees at a safe distance. Don’t plant any trees within 10 metres of your home and particularly large trees should be no closer than 40m.

The Association of British Insurers (ABI) has this guide to how far away different popular tree species should be from your home:

Source: ABI

Secondly, try to catch excess water. Avoid your soil from becoming waterlogged by using water butts to collect rainfall. Also, keep your guttering, pipes and plumbing well-maintained to avoid leaks.  

Can you get a mortgage on a house with subsidence?

While subsidence may put off many mortgage lenders, there are still plenty that will lend on a property that’s had subsidence in the past. A mortgage broker can help you find those more likely to approve an application. However, lenders will want to know that the subsidence has been completely resolved before they’ll consider lending.

I’m selling: How much does subsidence devalue a property?

This will depend on how serious the problem is and whether you have had the subsidence fixed. But even if you have, some buyers may still be nervous and it is still likely to reduce the amount you can get for your home and could make it harder to sell.

Selling a house with subsidence: Do I need to tell buyers?

Yes. You need to tell potential buyers if you’re selling a house with subsidence. If you don’t, you could be subject to legal action further down the line.

How long do you have to declare subsidence?

There’s no time limit on this. If you’re selling your house you’ll need to declare there has been subsidence, even if you fixed the problem 10 years ago.  And it’s always better to be up-front about these issues to avoid inevitable delays later on.

Buying a house with subsidence

So what if you’re buying a house with subsidence? Here’s what you need to consider.

Get a structural survey

When you are viewing properties keep an eye out for the signs of subsidence. Ask the seller and estate agent directly if the house has suffered from subsidence. But your enquiries shouldn’t stop there. If you are interested in buying a property that you suspect may have subsidence get a full buildings survey done, and flag with the surveyor you suspect there may be signs of subsidence. The survey should inform you if there is any risk of subsidence and whether further investigation is required. Your mortgage lender’s valuation is not a survey into the condition or structure of the property so will not highlight subsidence; you will need to get a full survey done yourself.

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Conveyancer checks

If repairs for subsidence have taken place in the past your conveyancing solicitor should get legal documents from the vendor to verify that the repairs were done to the standard set by the Building Research Establishment. These documents should include a formal Completion Certificate, which is issued by the council if the property has been underpinned, and a Certificate of Structural Adequacy, which should have been created by a building surveyor if the repairs were part of an insurance claim. Many repairs come with guarantees which you will want to have passed to you.

Subsidence insurance checks

Your conveyancer will be able to find out who the property is currently insured with and for how much. You should check that policy document to ensure the insurance company is aware of the history of subsidence and that there is continuation cover in the event subsidence were to occur in the future. You should shop around for home insurance to see what the options are as your choices may be limited or policies more expensive.

Buying a house with minor subsidence

If you’re considering buying a house with minor subsidence you’ll still want to consider it carefully. Even if the subsidence issue isn’t particularly serious and it has been fixed, you need to reassure yourself you can get insurance as a priority. And when it comes to sell in the future, you should be prepared for the history of subsidence, no matter how minor, to put off some potential buyers.

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