Homes In London Are Cracking As The Clay They Are Built On Shrinks

Homes across much of London sit on clay soil, which shrinks when it dries out and swells when wet. After five heatwaves this summer, that shrinking is pulling foundations apart, causing what's called subsidence — the slow sinking or settling of the ground under a building. Residents describe cracked walls, sticking doors, and shifted kitchens. Older Victorian and Edwardian houses, built with shallow foundations directly on the clay, are most at risk. Modern buildings with deeper foundations are largely spared.

The cost is adding up fast. UK insurance claims for subsidence hit a record in the second quarter of this year, averaging £20,000 (about $27,200) per household, up 15 percent from a year earlier. Payouts have jumped roughly 90 percent over four years, reaching £297 million. Fixing subsidence damage, through a process called underpinning that reinforces a building's foundation, can cost £20,000 to more than £100,000, and the damage itself can cut a home's value by up to 25 percent. Insurers, wary of unpredictable payouts, tend to respond to rising claims by excluding coverage or raising premiums.

The risk isn't confined to today's cracks. UK government researchers estimate 1.8 million properties, about 5 percent of the country's buildings, are likely to face this kind of shrink-and-swell subsidence by 2070, a figure that could rise to 4.2 million under more severe warming. The areas most exposed are dense parts of London, Kent, and southeast England.