This week’s heatwave is drying the ground hard – and for millions of homes built on clay soil, that is exactly when subsidence risk creeps up. A new interactive subsidence map lets you check the picture where you live.

The heatwave sweeping Britain this week is a welcome change for many. But for homeowners, prolonged hot, dry spells carry a hidden cost: they are one of the biggest triggers for subsidence.

 

When clay-rich soil dries out, it shrinks. As it shrinks, it can pull away from the foundations of the homes sitting on top of it, causing the ground to move and walls to crack. It is no coincidence that subsidence claims tend to spike after a long, hot summer – after the record heat of 2022, insurers reported a surge in homeowners reporting cracks, sticking doors and windows, and movement around their properties.

 

With another heatwave now gripping the country, a new interactive map from home insurance experts at Uswitch lets people check the indicative subsidence risk for their own town, city or council area.

Why heat is the trigger

Subsidence is the downward movement of the ground beneath a building. The most common cause in the UK is “shrink-swell” clay soil, which expands when wet and contracts when dry. A sustained heatwave dries this ground out from the top down, and the more it shrinks, the more stress it puts on foundations – particularly on older homes, and those with large, thirsty trees nearby drawing moisture from the soil.

 

That is why the risk is not spread evenly. The highest-risk clay soils are concentrated across London, the South East and the East of England, but pockets of vulnerable ground exist in many parts of Britain – which is why the map is worth checking street by street rather than assuming your region is in the clear.

Check your area

Uswitch has mapped the indicative risk using open British Geological Survey shrink-swell data, broken down to town, city and council level.

 

 

Readers can search their own area to see how it compares – and whether the heatwave is something their home is more exposed to than they realised.

The cost most homeowners underestimate

Subsidence is among the most expensive problems a home can face. The average subsidence claim runs to around £17,000 – the largest of any household claim type – and the British Geological Survey has projected that, under a high-emissions scenario, up to 4.2 million homes could be exposed to shrink-swell subsidence risk by 2070 as summers grow hotter and drier.

 

There is also a sting most people only discover when they claim: subsidence usually carries a far higher excess than standard home insurance, typically £1,000 to £2,500. So even when a home is covered, the homeowner can be left with a four-figure bill before the policy pays out.

What homeowners can do this summer

Experts say there are simple steps to take, especially during a heatwave:

  • Watch for the warning signs: new, diagonal cracks wider than 3mm (around the thickness of a 10p coin), particularly around doors and windows, and doors or windows that suddenly start sticking.
  • If you spot a crack, photograph it and keep an eye on it over a few months to see whether it is still moving.
  • If it is still changing, call a chartered surveyor for a diagnosis before involving your insurer.
  • Keep large trees and shrubs in check. Thirsty trees close to the house can pull significant moisture from clay soil in dry weather – but never remove a mature tree without advice, as that can cause its own problems.
  • Check your buildings insurance now, and look closely at the subsidence excess, not just the headline premium.

 

Leoni Moninska, a spokesperson for Uswitch said: “Subsidence is an area where homeowners can easily be caught out – both by the risk to their property and by the excess they’d face on a claim.

 

“If you spot a crack, photograph it and monitor it over a few months. If it’s still changing, call a chartered surveyor for a diagnosis before involving your insurer.

 

“Use our subsidence risk map to check your area. If needed, make sure your home insurance policy includes subsidence cover, and find out what excess you’d face – so you know you’re on the right policy for your home.”