Subsidence Surveys Explained
Subsidence occurs when the ground beneath a property compresses or sinks. This creates an unbalanced foundation. As the ground becomes unstable, the foundations become misaligned. This affects the property’s structural safety which then negatively impacts its value.
If you suspect your property is suffering from subsidence, you should hire a surveyor to inspect the building. They will check for subsidence and review any structural damage. They can then advise you on the next steps to take.
- What Causes Subsidence?
- What are Subsidence Surveys and How Much Do They Cost?
- What are the Signs of Subsidence?
- Difference Between Subsidence and Settlement
- How to Reduce the Risk of Subsidence
- What to Do if You Suspect Your Home Is Subsiding
- Treating Subsidence
- Find a Surveyor
- Learn More About Surveying
What Causes Subsidence?
Subsidence is commonly caused by the weather and how it changes the ground. Wet weather adds moisture, causing the soil to expand. Warmer months will then 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 shift during hot weather. This creates unstable ground. The foundations are then pulled as they shrink from dry, hot weather. This issue is often found in many areas of London where this soil type is common.
Droughts
If the area is prone to droughts, subsidence being present is more likely. This is because the soil dries out too quickly which affects the soil stability.
Tree roots and Japanese Knotweed
Environmental factors like trees and shrubs can be a common cause if they're close to a property’s foundation. Species such as willows and elm trees absorb water quickly, drying out the soil.
Japanese Knotweed is a destructive and dangerous plant. It can force its way through concrete and a building’s foundations. This then weakens the structural integrity of a building.
Shallow Foundations
This is particularly common in older properties. Older homes tend to be built from bricks and lime mortar. This can make them more flexible and more susceptible to subsidence.
Previously Mined Areas
Mining activity can be a major risk factor when it comes to subsidence. Former quarry or pit sites can cause instability as the materials decompose. This weakens the ground.
Leaking Drains and Pipework
A leaking drain can wash away or soften the soil underneath your property making it unstable and more likely to collapse. Leaky pipework and faulty water mains can also cause stability issues with the property.
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What are Subsidence Surveys and How Much Do They Cost?
There is no specific survey that can be carried out by a chartered surveyor that specifically focuses on subsidence. However, a surveyor will look for this during their reporting process.
You will need to have either a RICS Home Survey Level 2 or 3 carried out to check for potential subsidence issues. While a Level 2 survey can detect subsidence issues, a Level 3 survey provides a more in-depth report on the condition of the property. If you suspect an issue with subsidence, a RICS Home Survey Level 3 is recommended.
While there is no set subsidence survey cost, you can expect to pay around £630-£1,390 for a Level 3 survey. A Level 2 survey is less expensive and costs an average of £380-£640. The cost will vary based on the value of the property and the surveyor you choose to use. This survey is previously known as a Structural Survey.
If your property or the property you have purchased has signs of subsidence, a surveyor can provide you with advice on the next steps to take. This will be to contact a structural engineer. Structural engineers can carry out a "Subsidence Report", which is officially known as an FCI Ground Stability Report. It's useful to note that ground stability checks are part of the environmental searches carried out during the conveyancing process when buying a house.
For more information read: RICS Home Survey Level 3
What are the Signs of Subsidence?
Many homes will have cracks from the property settling. This is common and typically not a concern. 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, door frames and sticking doors
- Wrinkling wallpaper at wall or ceiling joints
- Sinking or sloping floors
- Skirting boards separating from the walls
How Do Surveyors Check For Subsidence?
A chartered surveyor will check for subsidence by carrying out internal and external inspections of the property. They will look at common signs stated above, paying particular attention to cracks in the walls and any visual signs of issues.
The sooner subsidence is discovered and diagnosed, the easier it will be to rectify. A chartered surveyor can assess the foundations and conduct a visual property survey. A ground survey and a structural survey are essential. They will help determine whether any damage has occurred.
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Difference Between Subsidence and 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. They can grow up to a width of 15mm, causing structural damage.
How to Reduce the Risk of Subsidence
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. You can have drain surveys carried out to ensure they are in working order.
- 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
- Keep a close eye on internal hairline cracks as these can be the start of subsidence cracks
What to Do if You Suspect Your Home Is Subsiding
You should seek expert advice and contact your home insurer immediately if you suspect your home is subsiding.
First, check that your insurance covers subsidence. Your insurer can then help you decide on the best course of action. You should speak to your local authority. They can provide you with information on subsidence in the area.
It’s recommended that you seek the expertise of a reliable, RICS-accredited surveyor. The survey most suited to detecting subsidence is the RICS Home Survey Level 3. The surveyor will highlight the probable and possible causes in the detailed report provided to you.
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Treating Subsidence
If the cause of the subsidence is determined to be minor, then it should be easily fixed. However, only an expert can provide you with the most suitable course of action. 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 additional structural support. This is done through a process called underpinning. The foundations will first be investigated and soil samples will be taken to determine the best course of action to take.
Your surveyor may decide to monitor your home before declaring whether the ground is sinking. This can take up to 12 months.
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FAQ’s:
What is Underpinning?
Underpinning is a construction method used to help strengthen a building’s 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 workers of considerable experience. Trying to solve the issue yourself or hiring someone under qualified 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 will 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. If you’re selling through an estate agent, they will also need to be aware of these issues.
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. In Scotland, a buyer is required to carry out a Home Report, any causes of subsidence will be highlighted to the buyer through this.
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 more expensive.
The seller can state 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. According to the Association of British Insurers, a policy excess for subsidence is around £1000.
This is 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.
Can a structural engineer carry out the subsidence survey?
Yes, a structural engineer can carry out an FCI Ground Stability Report which is also known as a subsidence survey. They will investigate any potential subsidence issues and provide you with a report on the risks and the next best steps to take. This typically occurs after you have had a RICS Home Survey carried out.
Does a Level 2 survey cover for subsidence?
A RICS Home Survey Level 2 can flag subsidence issues. It will highlight areas of concern with the structural integrity of a property. This report does have its limitations and is not as detailed as the RICS Home Survey Level 3. As a result, it’s recommended to have the Level 3 survey carried out.
Is subsidence covered by my insurance?
Subsidence is often covered by insurance. Every insurance company will differ and this is not a guarantee. This is why it’s important to contact them with subsidence concerns. They can then inform you of whether your policy covers this.
Most companies cover subsidence if this is the first time it has occurred. If a property has already had previous subsidence issues, they may not insure you for this.
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?
