Buildings are sinking and cracking in one of Europe’s largest cities

As heat waves dry out the city’s soil, the ground is shifting and shrinking, pulling buildings down with it.

(CNN) — As blistering temperatures baked London this summer, people started to notice strange things happening to their houses: zig-zagging cracks suddenly appeared across walls, doors got stuck, windows warped.

Extreme heat brings many problems for a country not built for it: Schools close, train tracks buckle and — it turns out — houses sink.

London, along with other parts of southeast England, is at the epicenter of a subsidence problem, which is being fueled by unusually hot and dry weather. As heat waves dry out the city’s soil, the ground is shifting and shrinking, pulling buildings down with it.

“Subsidence is one of the most damaging geohazards in the UK today,” said a spokesperson for the British Geological Survey, or BGS. And experts warn the problem is only going to worsen as humans continue to burn fossil fuels and heat the planet.

London, like many parts of the UK, is built on clay. When wet, it acts like a sponge, sucking up moisture and expanding; in hot and dry conditions, it loses water and contracts. It’s a process called “shrink-swell,” and when the shrink occurs unevenly under the foundations of a building, it can lead to subsidence.

The city is particularly at risk because the specific kinds of clay soils on which it sits contain expansive minerals that are highly susceptible to changes in moisture. It’s also typically exposed to some of the country’s hottest temperatures.

An important factor is trees and plants. When it gets hot, their roots drive deeper and further in search of moisture to suck from the soil, often seeking out the damper ground beneath nearby homes — drying it out and causing it to shrink.

Older properties tend to be more vulnerable to subsidence, often due to shallower foundations — and more than half of London’s homes were built before 1945.

Across many parts of the city, 100% of properties are projected to face possible or probable subsidence risk in 2030, according to data from the British insurance company Aviva. This includes central areas such as Kensington, the City of London and Westminster.

But it’s a problem that goes much wider than the capital. When subsidence expert Bob Gibson started in the business 40 years ago, the issue was mostly in London and the south-east of England. “But with climate change it is now affecting many other parts of the UK as well,” said Gibson, who is the director of Building & Structural Consultants.

Whenever there is a hot dry summer, there is a “surge” of subsidence claims, Gibson said. In 2025, when the UK endured an extraordinarily hot summer, the insurance industry paid out a record $415 million in subsidence-related claims, up 10% compared to 2024, according to data from the Association of British Insurers, or ABI.

The record may soon be broken. “This year is shaping up to be the biggest ever, as it is the second of two consecutive drought summers with multiple heatwaves,” Gibson said.

Insurers paid out more than $97 million for UK subsidence-related claims in the second quarter of 2026, and the average claim reached a record $27,000, more than $2,700 higher than the same period last year, according to the ABI.

“Following the extremely hot and dry weather we saw over July and August this year, it’s likely we’ll see more subsidence claims over the coming months,” said Louise Clark, general insurance policy manager at the ABI.

An Aviva spokesperson said the company had already seen an increase in claims this year and it will likely continue “unless there is significant rainfall.”

Subsidence is sometimes subtle and slow moving, but it can be hugely damaging and challenging to address.

There are two ingredients to consider in subsidence risk, said Brunella Balzano, senior lecturer in structural design at Cardiff University in Wales. The vulnerability of the building and the hazard itself. In the case of heat-driven subsidence, there’s nothing engineers alone can do to address the hazard. “We cannot remove climate change,” Balzano said.

So, they focus on the building. Interventions can include removing trees and vegetation or constructing barriers to isolate their roots from the house’s foundations and, at the more extreme and expensive end, underpinning the house by pumping concrete beneath the foundations.

As temperatures continue to rise, and subsidence claims spike, some experts fear insurers may no longer wish to take on the risk. “I think it’s possible … that in the near future, subsidence might not be insured anymore,” Balzano said.

In London alone, more than 26% of properties could be affected by 2070 if global warming continues at roughly the current pace, according to BGS data.

People are already struggling to secure insurance in high risk areas, Gibson said. “Insurers are jacking-up premiums hugely, or not inviting renewal of subsidence cover,” he said. This can make people fearful of reporting cracks to their insurers, which could lead to them invalidating their insurance, he added.

Subsidence is rarely a life or death issue. “It sits on the borderline, in between what’s really dangerous and what can be neglected for a while,” Balzano said. It’s nowhere near as dramatic as homes falling into the ocean, being ripped off their foundations by floods, or burned to the ground in a wildfire.

But it’s also not just an irritant. Subsidence can cause major damage, devalue homes, make them hard to sell and cost eye-watering amounts to fix. It’s one more part of the general underlying hum of anxiety-fueling challenges climate change is bringing to people’s lives.

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