How to tell if your home is at risk of subsidence and fix it without spending a fortune before it knocks a quarter of the value off your house: LUCY EVANS

Homeowners could see tens of thousands of pounds wiped from the value of their home this year in a so-called subsidence ‘super-event’, Money Mail can reveal.

An unprecedented summer of heatwaves and prolonged dry weather is expected to trigger the largest number of subsidence claims in more than 30 years, experts warn.

Millions could start to see large new cracks suddenly appear in their homes in the coming months, experts warn.

The majority of cases are down to soil drying up during prolonged periods without rain, as it causes the ground underneath homes to subtly move.

Insurers are bracing themselves. Last week, Aviva boss Amanda Blanc sounded the alarm, warning the insurer would have to top up its reserves to cover the expected surge in claims.

Plus, surveyors tell Money Mail they are expecting phones to ring off the hook at the end of summer when owners start to notice fresh cracks.

Spotting a new crack strikes fear into many homeowners. Subsidence can reduce a property’s value by as much as 25 per cent. Lenders will often refuse to offer a mortgage until it has been resolved.

Worried homeowners have already taken to social media, seeking reassurance from others. Hundreds have posted about ‘worrying’ or ‘scary’ looking cracks on social media site Reddit in the past month.

Fixing subsidence can cost £40,000 or more if you have to bolster the foundations of your home with concrete. But there are ways you can tackle it without breaking the bank.

Here, experts share their top tips on how you can save money – and how to spot the difference between a bad crack and a harmless fissure.

Why claims will soar

This summer’s drought poses a huge risk to homes sitting on sponge-like clay soil, says Andrew McColl, chairman of the Residential Property Surveyors Association.

‘In a wet winter it swells, and in a hot dry summer it shrinks, and a house sitting on it can move as the ground moves,’ he says.

‘What makes this year unusual is that many parts of southern England have had both extremes back to back. In those areas the ground has swollen and then shrunk further and faster than normal, and that is exactly the recipe for movement.’

As the clay soil loses moisture, it shrinks, which can weaken the support under the home and cause it to drop.

It means masonry and brick walls which sit on the foundation will shift position.

And the expected influx in claims is not simply driven by the extended dry spell this year – it comes after a very dry 2025.

Insurers paid out a record £307million for subsidence claims last year, according to the Association of British Insurers (ABI).

It is what the industry calls an ‘event year’ – a period where subsidence claims skyrocket. In the past 25 years, 2025, 2022, 2018, 2006 and 2003 were all identified as ‘event years’.

But this year is shaping up to be a ‘super event year’ for claims, according to Michael Lawson, chief executive of subsidence adviser Property Risk Inspection.

The soil moisture conditions so far this year are similar to the levels in 2025.

He says: ‘Insurers filled up their books with claims last year and thought that the very worst thing that could happen is for 2026 to be a big year. It’s the first “double tap” since 1990-91.

‘Hundreds of thousands of households got close to telling their insurer last year but it just didn’t seem bad enough. Insurers are now terrified.’

And this year, there’s already a backlog of jobs as professionals are booked up with claims from last year’s dry summer.

Lawson adds: ‘There’s no one to do the repairs. The supply chain is already straining under the weight of 2025.’

The British Geological Survey has warned that millions of homes in London, Essex, and Kent are at risk of sinking into the ground. 

In London, where the risk of subsidence is most severe, up to 26 per cent of homes could be affected within 45 years.

When to worry

Homeowners tend to panic when they spot a new crack in their wall – but that doesn’t always mean the house is subsiding.

So what should you look out for? Sullivan says the first thing you’ll notice is a stiffening of windows and doors. Frames can warp as the house moves, which means they may be more difficult to open or close.

Subsidence can also produce ‘step-like’ diagonal cracks as the ground moves.

Mr Sullivan adds: ‘Cracks usually occur on the corner of a bay window, for example, or the corner of a house. It tends to be a diagonal crack that’s much thicker at the top and thinner at the bottom.’

Close to staircases, around door frames or where walls meet the ceiling are also common places for subsidence cracks.

You should also look out for wallpaper that starts to wrinkle, ripple or tear without an obvious cause, according to the ABI.

If you spot a large crack, check whether it appears both inside and outside your home, as this can be a sign of a more serious issue.

Cracks typically appear suddenly at the end of a long dry spell. As a rule of thumb, subsidence cracks tend to be at least the width of a pound coin.

Hairline cracks that are two millimetres in width or less are not usually caused by subsidence and could be due to seasonal temperature changes or cracks in the plaster.

Lawson says you should look out for any changes in your home: ‘Is your house behaving as it normally would? Most people know their homes really well.’

Also note if a previously level floor is now uneven or if wallpaper that is unaffected by damp has begun to wrinkle, as these can also be signs.

The properties most at risk

If your home has subsidence, its value could be slashed by as much as a quarter, according to estate agents Greater London Properties.

This is because the structural issues can hit buyer confidence, as house hunters fear high repair costs and inflated insurance premiums.

In severe cases, this means a home originally worth £400,000 that then develops large cracks and structural issues, could be worth just £300,000 on resale.

Even if the subsidence is historic and is now well-managed, it could still wipe up to 10 per cent off a property price tag, says house buyers Property Rescue.

Plus, it may mean your home is unmortgageable as lenders view it as too large a risk. This will restrict your buying pool to cash buyers, unless the sinking is resolved.

The properties that are most vulnerable to subsidence this year are those built on sponge-like clay soil, which includes huge swathes of London, the South East and the East of England, as well as other pockets across the country.

Victorian and Edwardian properties are also more at risk of subsidence because their foundations are shallower than more modern builds.

Homes with extensions are particularly at risk, and McColl says he’s already seen movement in buildings attached to the main home.

He explains: ‘Conservatories, porches and garages have much shallower foundations and far less weight holding them down, so they move first.

‘I have seen more dropped paths and driveways this year than anything else.’ McColl has noticed big concrete drives with subsidence this year. The ground beneath the concrete has been sinking in the heat, creating a huge empty void where the drive drops down.

Trees planted near homes with clay-rich soil also pose a risk.

Plant roots soak up water all year round but during dry spells they can shrink the ground as their roots stretch out in the soil to find moisture. This shrinks the sponge-like soil which can in turn cause the ground to sink.

Older, larger trees are usually more of an issue than smaller saplings. Among the most likely trees to cause damage are oak, poplar, elm, horse chestnut and willow.

For example, an oak root can grow up to four feet below the ground within a decade – and spread out at the rate of a foot a year.

Brian Sullivan, of surveyors Hamblin Sullivan Associates, says many properties will see even more tree-related damage occur when it rains. He points out that vegetation is currently lying dormant in the hot weather, but when it starts to rain it will spring back to life. This means roots will suck even more moisture from the already dry clay soil, causing it to shrink and move under a home.

What insurance will cover

Make sure your insurance policy covers subsidence repairs and damages.

Most standard buildings insurance policies include cover for subsidence, but you may need to pay a higher excess, say £1,000, for repair works.

If you don’t have cover, you are likely to have to cough up thousands of pounds to fix the issue.

Lawson says insurers may have to fork out as much as £600million to policyholders if there are 50,000 claims this year, as there were in the 2003 event year.

Insurers paid out more than £72million in domestic subsidence claims between April and June this year as the heatwave took hold, with the average claim sitting at £20,000, according to ABI data.

That was more than £2,000 higher than in the same period last year. The sum is set to climb even higher if drought conditions in central and southern England persist.

If you notice a crack or other tell-tale sign, contact your insurer or a surveyor and ask them to visit. Even once the insurance company has visited and agreed there may be a problem, you must be patient as a professional check and work completion can take years.

The ‘diagnosis’ alone can take six months, which might include installing lasers to monitor how and where the property is sinking – and why.

No repair work can start until the root cause of the subsidence is identified.

After any necessary work has been completed you may also have to wait a further six months for a ‘certification of structural adequacy’ to show that the property is stable. This is vital to sell the property at a later date without it losing market value.

How to tackle the problem

How much the repairs will cost depends on the severity of the sinking but in the most serious of cases invoices for the building work required can exceed £100,000.

Solutions for extreme subsidence involve resin injections that fill underground voids or underpinning, where foundations are extended into stable ground.

Most subsidence, however, doesn’t need these heavy repairs and can be solved by fixing the underlying issue, such as removing a thirsty tree.

But before you take a chainsaw to the oak, get proper advice, especially if the tree is close to a neighbour’s home. This is because sometimes, removing a very thirsty tree stops it from drinking large volumes of water each day, causing the surrounding clay soil to swell. This can push foundations upward, causing even more structural damage.

Always contact your insurer, a tree surgeon and a structural engineer first. The Arboricultural Association can provide details of accredited tree surgeons in your region.

McColl says plants that are especially thirsty, such as weeping willows and eucalyptus, should be planted far away from a home and vegetation should be kept off the walls.

You should avoid planting a tree that has the capacity to grow beyond six metres within ten metres of your home.