In this brief guide, we will define what subsidence is and how you can ensure you are not buying a home with subsidence.

What is subsidence?

Subsidence is a very specific issue that occurs when the ground under your house collapses, or sinks lower, taking some of the building’s foundations with it. This puts a strain on your home’s structure as one side sinks due to your home foundation becoming uneven. This causes cracks to appear on your walls.

When subsidence happens the ground underneath your house sinks and the foundations of the house become misaligned. This is usually the case when different parts of your property are sinking at different rates.

Subsidence is quite different from Heave which is where parts of the ground in your home begins to push the foundations of your home upward. 

Subsidence is also quite different to a landslide or landslip which is when the ground where your home was built starts washing away slowly.

Subsidence is also more common in areas with clay-rich soil, like much of south-east Britain. The Subsidence Support website has a useful map of areas at risk of subsidence.

Subsidence vs Settlement

There is also a 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 some home insurers do not cover settlement.

Is a crack the main sign of subsidence?

Cracks are a major sign of subsidence but this doesn’t mean every crack in your home is a sign of subsidence. Cracks could form due to your walls or ceilings welling and shrinking due to temperature changes between the summer and winter months. Cracks could also develop on walls as the plaster dries out. This is very common with new homes.

What are the signs of subsidence?

A crack caused by subsidence is likely to be:

Wider than 3mm – that’s the width of a 10p coin

Visible on both the outside and the inside of your home

Diagonal and usually wider at the top than the bottom

Located close to a door or window

Cracks aren’t the only sign that you may have a subsidence problem. 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. 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.

What causes subsidence?

Subsidence is usually caused by a large loss of water in the ground. This can happen to certain types of rocks such as fine-grained sediments. As the water is withdrawn the rock begins to shrink due to the holding element(the water) vanishing. Once the water has been withdrawn to a certain point, the ground will begin to sink in as the rocks fall and crumble on themselves.

What increases the risk of subsidence?

There are a few things which increase the risk of subsidence and you may want to be aware of this when you are buying a house so you can watch out for them.

It is true that some homes will be more at risk of sinking due to external factors which make the subsidence appear worse. Examples of this could be the type of soil they sit on and the weather conditions throughout the year.

The main things which can increase the risk of subsidence include:

Clay

Because the form of clay changes a lot with the weather, it is more likely to increase the risk of subsidence when the weather is very hot and dry as it can shrink which makes the ground very unstable and may cause it to sink

Trees

Trees can also increase the risk of subsidence as large trees which are close to your home can absorb all the moisture in the ground which causes the soil underneath your home to become dry and begin to crack or sink. Most cases of subsidence in the UK are a result of trees absorbing all the moisture. You should avoid planting trees close to your house. This means within 10 metres and avoid buying houses where a large tree is within 40 metres.

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

SpeciesNormal Mature Height (m)Safe Distance (m)
Apple/Pear1210
Ash2321
Beech2015
Birch1410
Cypress2520
Cherry1711
Damson1211
Elm2530
Hawthorn1012
Holly146
Horse Chestnut2023
Laburnum129
Laurel86
Lime2420
Magnolia95
Maple2120
Oak2430
Pine298
Plane3022
Plum1211
Poplar2835
Sycamore2417
Spruce187
Walnut1814
White Beam/Rowan1211
Willow2440
Yew125

Source: ABI

Drought

Drought can also be a serious cause of subsidence as it can cause the soil underneath your home to be very dry and begin to crack and eventually sink.

Leaks

Leaks can also be a big cause of subsidence as they make the soil underneath your house become soft and gradually begin to wash away. This can cause the ground below your house to sink

Mining

If your house is built close to a mining area then it could be at risk of subsidence as the materials used to fill the mines decompose and gradually begin to shift. This could affect the foundation of your home and force cracks to occur. You should ensure you get a full home survey report before buying a house which is close to a mine.

Age of house

Period properties(Victorian and Edwardian houses ) have a greater risk of subsidence as these homes will usually have more shallow foundations(less than the 1 metre requirement).

Construction of house

The construction of the house can also increase the risk due to the types of materials that may have been used to build the home.

I’ve spotted suspicious cracks in my house, what should I do?

If you have spotted suspicious cracks in your house and you think this might be subsidence then the first thing to do is to get a professional opinion. 

You can do this by reporting the matter to your home insurance company who will then send out a surveyor to inspect the cracks and let you know if it is truly subsidence. If it is subsidence your home will then be monitored and checked constantly to determine if the foundation is sinking. This process can take up to a year.

You may also want to get an independent opinion without informing your home insurance company as the likelihood that your insurance premiums will now begin to rise for every year after are now incredibly high. This may be the case even if you don’t end up having subsidence.

A professional opinion before informing your insurers may, therefore, be the best course of action if you find a suspicious crack in your house.

Is subsidence covered by home insurance?

Most home insurance providers will cover subsidence as a standard clause but you should read your home insurance documents to be sure and ask your home insurance company if they cover subsidence in writing. Home insurance providers will usually also cover heave and landslip but they will not cover the costs of preventing these things from happening.

What are the signs of subsidence in a house?

The signs of subsidence in a house include:

Cracks in your wall, ceilings or outside your house
Cracks which seem to be expanding
Cracks which have newly appeared after a period of very dry weather
Wallpaper which is rippling without any damp
Sticking of doors and windows.

Can you fix subsidence?

Yes, you can fix subsidence by either targeting the root of the problem. E.g a tree or carrying out structural repairs to strengthen the foundation of the house. This is known as underpinning.

Can you live in a house with subsidence?

Yes, you can live in a house with subsidence without major issues. Subsidence can be managed by some structural work or by removing the cause of the problem which makes living in a house with subsidence much easier.

Do I have to declare subsidence when selling?

You must declare subsidence when selling your house if not you could be sued after the buyer has moved into the home.

As a homebuyer you should feel confident when buying as long as you have had the seller’s written answers in writing to prove that they denied the existence of subsidence. This also means you should hopefully be able to sell the property in the future and will also need to declare the subsidence.

Can subsidence be reversed?

In some cases, subsidence can be reversed and repaired without the need for any foundation work or underpinning. This will usually involve finding the root cause of the issue and carrying out work such as repairing pipes or dealing with trees which are absorbing all the moisture.

Can you get a mortgage on a house with subsidence?

Yes, you can get a mortgage on a house with subsidence but the mortgage lender will likely want a full survey report (at your cost) to understand the extent of subsidence and if they will be willing to lend on the house.

If you can secure home insurance on the property then most mortgage lenders will offer you a mortgage on a house with subsidence.

How do you stop subsidence?

You can stop subsidence by doing the following things:

Call in a professional to cut down trees
Pick trees carefully to avoid them absorbing all the water
Keep an eye out for cracks
Make sure home improvements follow building regulations

What causes subsidence UK?

The main things which cause subsidence in the UK are the roots of trees. Tress account for over 70% of the subsidence cases reported in the UK. Tree roots absorb water for photosynthesis and this starves the surrounding ground of water.

Can leaking drains cause subsidence?

Leaking drains can cause subsidence as drains are built to take water to the ground beneath your house and if the leaking drains don’t take water to this ground then it can cause it to become very dry and begin to crack which eventually causes the foundation to sink in.

Can hot weather cause subsidence?

Hot weather can cause subsidence as it means the water which should be beneath the ground is absorbed and causes the foundation to form cracks due to a lack of moisture. Eventually, the foundation will collapse and begin to sink lower at an uneven rate. This will then form cracks on the wall, floors and ceilings.

Is subsidence covered by insurance?

Most home insurance policies will cover the damage resulting from subsidence as a standard practice.

Should you buy a house with subsidence?

You should buy a house with subsidence as long as the subsidence is not very severe and at risk of causing serious structural damage. You should get a home survey report in order to analyse if subsidence is a serious issue in the home you want to buy. If you cannot get home insurance for the property which covers damage from subsidence then you should not buy the house.

What is underpinning?

Underpinning is a structural process used to strengthen the foundation of a home which has been affected by subsidence.

How long does it take to underpin a house?

It can take as long as 6 weeks to underpin a house. This is due to the fact that the process can take much longer than expected as issues will usually creep up.

Can you sell a house that has been underpinned?

Yes, you can sell a house that has been underpinned. Most mortgage lenders will be happy to lend on a property which has been underpinned as long as they can view a report stating the work carried out.

Does subsidence always need underpinning?

Subsidence may not always need underpinning, it could be fixed by simply dealing with the root causes of the subsidence such as trees or leaking drains. An expert will determine if underpinning is necessary. In some cases, no work may be needed.

Do I have to declare underpinning when selling my house?

You are legally obliged to declare underpinning to the potential buyer of any underpinning work which has been carried out if not you can be sued after you have sold the home.

In this brief blog, we defined what subsidence is. If you have any questions or comments please let us know.

John Bate

John has 22 years of experience in financial services. This spans across financial research, financial services (As a qualified mortgage broker and underwriter), financial trading and sales at global investment banks. While working as a publishing research analyst, he covered European bank credit and advised institutional clients on investment strategies at both JP Morgan and Societe Generale. John has passed all three levels of the CFA (Chartered Financial Analyst) programme.