Subsidence: What Does It Mean and What are the Signs?

Written by Martha Lott Reviewed by Mike Ashton

8th Sep 2021 (Last updated on 16th Mar 2023) 6 minute read

What Causes Subsidence?

Subsidence is most commonly caused by the weather as it changes the ground. Wet weather will add moisture and make the soil expand. Whilst warmer months will dry the soil out and make it contract. This constant fluctuation causes the ground to become unstable.

Other causes of subsidence include:

Clay soil

Clay soil can shrink, crack and even shift during hot weather. This creates unstable ground. The foundations are then pulled as it shrinks from dry, hot weather. This issue is often found in many areas of London.

Droughts

If your area is prone to droughts, you’re more likely to experience subsidence as the soil dries out too quickly.

Tree roots and Japanese Knotweed

Trees and shrubs can be a major factor if they're close to the property’s foundation. Species such as willows and elm trees absorb water quickly, drying out the soil.

Japanese Knotweed is also a destructive and dangerous plant. It can force its way through concrete and a building’s foundations. This then weakens the structure.

Shallow foundations

This is particularly common in older properties. Older homes tend to be built from bricks and lime mortar which can make them more flexible. This then makes them less likely to be damaged by subsidence.

Previously mined areas

Previous and current mining activity can be a major risk factor. Former quarry or pit sites can cause instability as the materials decompose. Thus weakening the ground.

Leaking drains

A leaking drain can wash away or soften the soil underneath your property making it unstable and more likely to collapse.

What are the Signs of Subsidence?

Many homes will have cracks from the property settling. But they are an essential factor when spotting the early signs of subsidence.

Cracks that appear from subsidence are quite distinctive making them easier to spot. These types of cracks are likely to:

• Be wider than 3mm (or a 10p coin)
• Appear both inside and outside the property
• Be found around doors and windows
• Run diagonally and look more narrow at one end

Other common signs of subsidence include:

• Warped windows or door frames
• Wrinkling wallpaper at wall or ceiling joints
• Sinking or sloping floors
• Skirting boards separating from the walls

Always seek professional advice if you suspect your property is subsiding. The sooner it’s discovered and diagnosed, the easier it can be to rectify. Hire a chartered surveyor to assess its foundation and conduct a property survey. They can then determine whether any damage has occurred.

Subsidence vs Settlement

Subsidence is caused by downward movement where the ground becomes unstable. Settlement is a result of downward movement caused by the soil being compressed by too much weight.

Settlement is common and typically occurs 10 years after a property is built. Some insurers will cover subsidence but won't cover settlement.

When a property has signs of settlement, you will begin to see cracks in the walls. These are usually harmless and can be plastered over. However, they can grow up to a width of 15mm, causing structural damage.

How to Reduce the Risk

To help prevent the risk of subsidence, you can:

• Remove any trees or shrubs that are too close to your property - Ask or hire a tree surgeon for advice on how to safely remove these
• Regularly prune any trees that are close to your property but within a safe distance
• Do not plant any trees within 10 metres of your home - 40 metres for larger trees
• Avoid leaks by maintaining any external guttering, pipes or plumbing
• Try to avoid excess water seeping into the ground. This causes the soil to become waterlogged - water butts can be used to collect rainfall
• Ensure you organise the right home survey so any signs of subsidence can be detected

What to Do if You Suspect Your Home Is Subsiding

You should seek expert advice and contact your home insurer immediately.

First, check that your insurance covers subsidence. Your insurer can then help you decide on the best course of action.

It’s recommended that you seek the expertise of a reliable, RICS accredited surveyor.

The survey most suited to detecting subsidence is the RICS Level 3 Survey (also known as a building survey). It’s the most thorough survey type and includes an inspection of the building’s structure.

Basic signs may be discovered in a RICS Level 2 Survey. But a Level 3 survey is recommended to receive a more definitive answer.

Treating Subsidence

If the cause of the subsidence is determined to be minor, then it should be easily fixed.

Only an expert can provide you with the most suitable course of action, but for minor issues, this could be:

• Removing any obstructing trees or vegetation
• Repairing damaged drains or pipes
• Demolishing and rebuilding garages or extensions that have caused instability

If the damage is severe, you may need more structural support. This is done through a process called underpinning. The foundations will first be investigated and soil samples will be taken.

Your surveyor may decide to monitor your home before declaring whether the ground is sinking. This can take up to 12 months.

What is Underpinning?

Underpinning is a construction method used to help strengthen foundations. The soil is excavated and replaced with the appropriate materials needed to repair the structure.

It’s often an expensive and invasive method. However, according to the Royal Institution of Chartered Surveyors (RICS), less than 10% of properties affected by subsidence need underpinning. It’s often used as a last resort.

No matter what course of action you’re recommended, you must always consult with experienced workers. Trying to solve the issue yourself or hiring someone underqualified could make the damage worse and cost you more.

For more information, read what is underpinning?

Can You Sell a House with Subsidence?

Many properties with a history of subsidence take longer to sell. They may not sell at all if the damage is severe.

Mortgage lenders may be reluctant to approve mortgages for the property. It can also be difficult to obtain buildings insurance. Treating and solving the issue is the best course of action when selling a house with subsidence.

If you’re selling a property with subsidence, you cannot conceal this information from buyers. To encourage interest, you will need to show that you’ve dealt with the problem as accurately as possible. Stress that this has been done by professionals and that the work abides by building regulations.

You can also show potential buyers your survey report, but they will likely ask to conduct their own.

Should I Buy a House with Subsidence?

You may struggle to obtain a mortgage for a property with subsidence. Many lenders will not approve a loan for a property that is deemed at risk.

You should first find out who the property is currently insured by and for how much. You should also compare insurance quotes as the choices can be limited and expensive.

If the seller states that the repairs for the subsidence have taken place, your conveyancing solicitor should obtain the legal documents to verify this. You must find out if the work is to the standards set by the Building Research Establishment.

What is Subsidence Excess?

Subsidence excess is the amount you have to pay when making a claim for subsidence with your insurance provider.

It’s usually a one-off payment. But it can increase depending on whether there was damage and how significant it was. The payment required varies and can rise if your property has been previously affected.

Learn More About Surveying

This is part of our guide to surveying. In our next article, we look at underpinning. To learn more, read what is underpinning?