Subsidence: What it is, how to identify it and what can be done

Surveyors have issued a stark warning regarding the millions of UK properties at risk of subsidence, with this year’s heatwave and drought seen as contributing factors, bearing a striking resemblance to the heatwave of 2018.

Earlier this summer, record heatwaves were forecast which the Met Ofice has since called a “milestone” in UK climate history. This captured the attention of keen-eyed surveyors across the UK who universally predicted a rise in subsidence levels, and so too the implications that might bring about. 

In a recent article by The Independent, a number of insurers also had their say on the increasing levels of subsidence, revealing that they have seen a “significant spike” in subsidence-related claims, particularly in areas severely affected by drought. 

Water scarcity has led to drier soils, which is particularly problematic for regions with clay-rich soils, such as the southeast and the midlands, among many other areas. Properties in places such as these are at heightened risk of subsidence. 

The risk has been echoed by the Royal Institute of Chartered Surveyors (RICS), the global professional body for surveyors. Gary Strong, the Chair of International Fire Safety Standards at RICS and a former subsidence surveyor, said to The Independent that although building regulations have changed for modern homes, it is the older stock that remains most at risk.

“The existing housing stock is Victorian or built in the 1920s or Thirties, and is at risk because their foundations are very shallow,” Strong said, noting that hairline cracks appearing in walls during summer will typically get worse by Autumn, which is when the majority of subsidence claims are likely to be made – a point evidenced by insurance companies across the country. 

One of the UK’s foremost home insurers told The Independent that compared to the same period in 2021, claims for subsidence had risen 218% in the first two weeks of August. 

Other insurers have lent their expertise to the conversation, including LV=, More Than and Allianz, all of whom agree on these patterns and are bracing for record levels of claims not seen since the aftermath of the 2018 heatwave. 

Although this year’s heatwave has since passed, parts of the UK are still reeling from the effects of drought. As we move through the next couple of months into Autumn, subsidence will continue to be a real and persistent threat to homeowners and investors across the country, so it’s important to know what to look for.

Map of subsidence vulnerability in the UK. Credit: Cranfield University

What is subsidence and how is it caused?

Subsidence can be a huge issue for homeowners. Ground subsidence often relates to the moisture content in the soil under a property. In a nutshell, subsidence is a downward shift in the ground surface which compromises the structural integrity of the property, and it is usually something that occurs over time rather than suddenly. There are a number of causes, both natural and man-made.

What are the natural causes of subsidence?

• Soil shrinking or swelling
• Trees and vegetation
• Movement of soil
• Decomposition of soil
• Drought

What are the man-made causes of subsidence? 

• Mining activity
• Water damage
• Construction work
• Poor foundations
• Heavy traffic

What are the signs of subsidence?

There are numerous telltale signs of subsidence. Homeowners should be vigilant because the sooner subsidence issues are identified the quicker they can be resolved. The longer subsidence goes unchecked, the higher the chance of a failed insurance claim. Subsidence can be easily remedied if caught early enough, so it is important to consistently check for the signs. 

As stated by RICS, the signs of subsidence are as follows:

• New or expanding cracks in plasterwork
• New or expanding cracks in outside brickwork
• Doors or windows sticking for no particular reason
• Ripping wallpaper that isn’t caused by damp

How do subsidence surveyors identify and respond to subsidence issues?

A homebuyer survey can give an initial indication of subsidence risk. These generally start with a visual investigation, identifying things like small cracks in walls. However, not all structural flaws are symptomatic of subsidence, so to really understand whether or not a home is at risk of subsidence, a more in-depth subsidence survey is necessary.

This could take the form of a ground survey, for example, and will show the extent and cause of subsidence if it is present at all.

During this subsidence survey, a professional will attend the property and conduct the necessary investigations, looking for tell-tale signs of subsidence like sticking doors and windows. Not all subsidence issues are immediately evident, so it could take some time to diagnose, with the property and its defects observed over a period of time.

Geographical surveys may also be necessary. These can identify unstable soil or issues with drainage that could lead to deeper subsidence issues if not straight away, then sometime in the future. 

The surveyor can then advise on the best course of action to remedy any issues that may cause short or long-term issues due to subsidence, while also communicating with the insurance company and providing the evidence necessary for any subsidence claim.

How can surveyors deal with increasing levels of subsidence surveys?

There are a number of surprising or unexpected issues that increasing levels of subsidence can give rise to. Heatwaves and droughts that cause a spike in subsidence can have wider implications for the property industry, ultimately impacting prospective homebuyers or vendors. 

For example, a raft of subsidence issues (and the subsequent claims) may cause unease among mortgage lenders, who may be more hesitant to issue mortgages in areas with a higher risk of subsidence.

As a result, mortgage applications could slow down due to the increasing number of checks lenders must carry out. Remortgaging and mortgaging for the first time could be delayed significantly, which could have a knock-on effect on the wider property market. 

Speaking to The Independent, Gary Strong said that it is likely around October or November, when people are trying to remortgage or sell due to rising interest rates, that valuers will be paying particular attention to signs of subsidence. 

Strong said: “Any cracking found could then result in structural engineers’ reports being required to reassure lenders. Inevitably that slows the whole thing down and creates a claim against the insurance company.”

In addition to this, there is the inevitable added workload for surveyors that widespread concerns typically give rise to. Given that surveyors across the country are already working through record caseloads, this can cause backlogs and bottlenecks which, again, impact the wider economy.

In the face of rising demand for subsidence surveys, surveyors are urged to consider more streamlined methods to conduct their work. The adoption of technologies and digitised surveying workflows could relieve some pressure on surveyors, enabling them to handle an increasing volume of surveys while still maintaining the same high standards surveying requires.

Over the next few months, we will certainly see how the increasing threat of subsidence pans out and affects the wider economy. For now, experts ask consumers to stay mindful of the signs of subsidence and to contact a professional at the earliest opportunity.