UK homeowners could see tens of thousands of pounds wiped from their property values this year as an unprecedented summer heatwave triggers a major subsidence super event across the country.
Experts warn that millions of properties could develop large structural cracks in the coming months as prolonged dry weather causes ground under foundations to shift. Insurers and surveyors report that the dry spell, following an unusually dry year in 2025, is set to prompt the highest volume of subsidence claims in more than 30 years.
Subsidence can slash a home's market value by up to 25 per cent while causing lenders to refuse mortgages until repairs are complete. Concerned homeowners have turned to social media for advice, with hundreds posting on Reddit in the past month about scary looking cracks appearing in their properties.
Fixing severe structural movement can cost £40,000 or more when foundations require concrete reinforcement, though experts emphasize that early detection and minor interventions can prevent major expenses.
Surging claims and clay soil risk
The sudden surge in structural risk stems from extreme weather acting on clay soil, according to Andrew McColl, chairman of the Residential Property Surveyors Association. Clay soil expands during wet winters and contracts during dry summers, causing properties resting on it to move.
McColl explained that many areas in southern England experienced back-to-back weather extremes this year, causing ground to swell and then shrink faster and further than normal. As clay soil loses moisture and contracts, support beneath foundations weakens, shifting masonry and brick walls out of alignment.
Insurance companies are preparing for an unprecedented volume of claims. Aviva chief executive Amanda Blanc warned last week that the insurer will top up its financial reserves to cover expected payouts. Surveyors also expect a surge in calls at the end of summer when property owners notice fresh cracking.
The double tap super event
The current dry spell follows a record year for insurers in 2025, when the Association of British Insurers recorded £307 million in subsidence payouts. The industry designates high-volume claim periods as event years, with 2003, 2006, 2018, 2022 and 2025 all reaching that threshold.
Michael Lawson, chief executive of Property Risk Inspection, said 2026 is shaping up to be a super event year because soil moisture levels match those of 2025. Lawson noted that this marks the first double tap consecutive dry spell since 1990 and 1991.
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, Lawson said. He added that hundreds of thousands of households came close to reporting claims last year, leaving insurers terrified. Lawson warned that repair supply chains are already straining under 2025 backlog work, leaving few contractors available.
Industry estimates suggest insurers could face payouts reaching £600 million if claim volume reaches 50,000, matching levels seen during the 2003 event year. Meanwhile, the British Geological Survey warned that millions of homes across London, Essex and Kent are at risk of sinking. In London, up to 26 per cent of properties could suffer effects within 45 years.
How to spot subsidence cracks
Homeowners often panic upon discovering wall cracks, but surveyors note that not all fissures indicate structural failure. Brian Sullivan of Hamblin Sullivan Associates said the initial sign of subsidence is often stiffening doors and windows as shifting frames warp out of shape.
Sullivan explained that subsidence creates step-like diagonal cracks that are noticeably wider at the top than at the bottom. These typically appear near bay windows, house corners, staircases, door frames, and wall-ceiling junctions.
The Association of British Insurers notes that sudden rippling, wrinkling or tearing of wallpaper without dampness also signals ground movement. Cracks that appear suddenly after dry spells and show on both interior and exterior walls require immediate inspection.
True subsidence cracks are typically at least the width of a pound coin. Hairline cracks measuring two millimetres or less are generally harmless, resulting from plaster drying or routine seasonal temperature shifts. Lawson advised owners to monitor whether properties behave normally, noting that unlevel floors can also indicate shifting foundations.
Property values and vulnerable homes
Structural damage heavily impacts property values and marketability. Estate agents Greater London Properties reported that subsidence can slash property values by 25 per cent as buyers fear repair costs and higher insurance premiums. A house worth £400,000 could drop to £300,000 on resale.
House buyers Property Rescue noted that even historic, fully repaired subsidence can reduce property value by up to 10 per cent. Mortgage lenders frequently refuse financing on affected homes, restricting sales to cash buyers until stability is proven.
Properties built on clay soil across London, the South East and the East of England face the highest threat. Victorian and Edwardian buildings are particularly vulnerable because they feature shallower foundations than modern constructions.
Attached structures like conservatories, porches and garages are often the first to shift. McColl explained that these extensions have shallower foundations and lighter weight, causing them to drop earlier than main structures. He noted a sharp rise in dropped paths and concrete driveways this year, where shrinking soil creates hollow underground voids.
Thirsty trees on clay soil compound ground movement by extracting groundwater. Oak, poplar, elm, horse chestnut and willow trees pose the greatest risk, with an oak root growing up to four feet deep within a decade and spreading a foot each year. Sullivan warned that dormant trees will absorb massive amounts of water when rain returns, shrinking soil further and aggravating structural movement.
Insurance claims and repair options
Standard buildings insurance policies generally cover subsidence repairs, though policyholders usually face a dedicated excess of around £1,000. Without coverage, repairs can cost tens of thousands of pounds out of pocket.
ABI figures show insurers paid out more than £72 million in domestic subsidence claims between April and June this year as heatwaves took hold. The average claim rose to £20,000, which is more than £2,000 higher than the same period last year. Total payouts will increase if dry conditions persist across central and southern England.
Homeowners who suspect subsidence should notify their insurer or a qualified surveyor promptly. Investigating structural movement takes time, with initial diagnosis often requiring six months of laser monitoring to determine how and why a building is moving before repair work begins.
Once repairs conclude, property owners must wait an additional six months to obtain a certificate of structural adequacy, which is necessary to restore full market value and secure mortgageability for future buyers.
Repair costs depend on damage severity, with extensive structural work exceeding £100,000. Major remedies include injecting expanding resin to fill subterranean voids or underpinning to extend foundations into stable ground strata. However, most cases do not require major engineering and can be resolved by addressing root causes such as thirsty vegetation.
Experts warn against removing trees without professional guidance. Removing a thirsty tree suddenly can cause dry clay soil to absorb excessive water and swell, creating ground heave that forces foundations upward and causes severe structural damage. Property owners should consult insurers, structural engineers, and tree surgeons accredited by the Arboricultural Association before taking action.
McColl advised that thirsty species such as weeping willows and eucalyptus should be planted far from buildings, vegetation should be kept off external walls, and trees capable of growing beyond six metres should not be planted within ten metres of a home.
