Homeowners face paying thousands of pounds for retrofits to make their homes habitable as the climate warms, experts have warned.

More than half a million homes have been built since 2017 that will need to be retrofitted to ensure they stay cool, despite the Government acknowledging at the time that “urgent action” was needed to address overheating.

By 2050, heatwaves like that seen in 2019, when the UK recorded a new all-time high temperature of 38.7C, are expected to happen every other year, according to assessments from the Met Office.

The Climate Change Committee, the Government’s statutory advisers, has estimated the costs of retrofitting cooling features into a property to be £9,200, compared to £2,300 when done at the building stage.

“Since the last climate change risk assessment, when the government recognised this as a risk to people in the UK, we’ve built almost half a million new homes, which overheat, in our already hot summers, and that will get worse in the future,” said Baroness Brown, chair of the CCC’s Adaptation Committee.

“And those new homes are now locked in to higher retrofit costs, which are four to five times the cost it would have been to address overheating at the time they were built.”

The CCC called for the introduction of new regulations to ensure developers were not building homes that are “uninhabitable as temperatures rise”. 

Some 8,000 deaths annually can be attributed to high temperatures in the UK, according to a study from Monash University this week.

Measures that can easily be incorporated when building new homes include avoiding large south-facing windows, including external shutters, trickle vents, green roofs, and green walls covered in vegetation.

Nicki Percival, 31, who works in regulatory affairs, bought a newly built townhouse in 2019 in the Cotswolds with her partner, but was forced to install an air conditioning unit after suffering 27C temperatures in her bedroom throughout that summer.

‘In summer it’s a nightmare’

“The extreme heat in the summer was definitely a shock. It’s just a bit crazy,” she said. “We open windows at the front and back, but they’re very small and it just doesn’t seem to have any effect.”

Many new homes are built with improved energy efficiency, which can exacerbate overheating in the summer.

Ms Percival said. “The house just won’t lose heat. In the winter it’s great, in summer it’s a nightmare.” The AC installation cost £1,000 as it was carried out by her father, a trained installer, but would otherwise have cost double.

The problem of overheating is not limited to new builds. Nearly a fifth of bedrooms reached average temperatures of 26.9C during the 2018 heatwave, the joint hottest summer on record, according to a survey by Loughborough University for the business department.

Guy Newey, a former advisor to energy minister Amber Rudd, said there was a risk the Government faced a backlash over costly retrofits.

“The homes we are building are pretty useless from a heating and cooling experience. And that’s partly because the enforcement measures are pretty weak,” he said.

“If I’d bought a home built in the last ten years and had to do a retrofit because it’s not fit for purpose, I would be furious. Because it’s not like climate change was a secret ten years ago,” he said.

A government spokesperson said: “The UK has a strong track record in improving the energy performance of its homes – with 40 per cent now above Energy Performance Band C, up from just 9 per cent in 2008.

“We will shortly set out our proposals to reduce the risk of overheating in new residential buildings as part of our response to the Future Buildings Standard consultation.”