Badly designed buildings can have strange consequences. In August 2013, sunlight concentrated by the curved exterior of a newly constructed skyscraper in London was so intense that it melted parts of a nearby car. This wasn’t the first time architect Rafael Viñoly had fallen foul of the sun. A Las Vegas hotel that he designed concentrated rays onto the pool area—singing hair and melting loungers. It was nicknamed “Death Ray Hotel.”
Unsuitable buildings spell worse trouble for the people inside them. More than half of the UK’s homes already suffer from overheating, but thanks to climate change, summers are getting hotter and heat waves are becoming more frequent. At best, an overly hot home is an unpleasant place to live or work. But for the most vulnerable people, overheating can be deadly. And things will continue to get worse unless the UK comes to terms with its current—and future—climate and starts adapting homes to suit long, hot summers.
Most of Britain’s homes belong to a bygone era. Nearly 38 percent were built before 1946—a higher percentage than in any European Union country. Often these are small, terraced houses that struggle to dissipate heat coming in through the windows. More modern dwellings bring their own problems. Shiny new tower blocks built with panoramic windows look the part, but they are notorious heat traps—a problem compounded by the fact that it’s often impossible to open their windows.
“Most of these homes were designed for a completely different climate,” says Anna Mavrogianni, a professor at the Bartlett School of Environment, Energy, and Resources at University College London. Historically, homes in the UK were designed to trap the sun’s rays and minimize heat loss during mild summers and cool winters. There’s a reason the aspirational suburban British house—think of Mick and Pam’s bungalow in the sitcom Gavin & Stacey—features big patio doors that open onto the garden. When sunny days are a scarcity, you want to maximize the amount of sunlight your building captures.
The problem is that warm days are no longer scarce during the summer months. The years 2012-2021 were on average 1 degree Celsius warmer than the period 1961-1990, and all of the UK’s top 10 warmest years have occurred this century. This issue is compounded when you consider where the UK’s overheated homes are located. The paved streets and cramped buildings of London trap heat, making the city up to 10 degrees Celsius warmer than surrounding areas. And not only is the capital the most densely populated part of the UK, it also has a higher proportion of small apartments—usually the worst kind of dwelling, from a heat perspective.
Overheated homes are bad news for a variety of reasons. Warm bedrooms lead to disrupted sleep, which can mean reduced cognitive function or mood changes. Hot temperatures are also linked to reduced productivity—a problem compounded if people swap air-conditioned offices for sweaty home offices. Most seriously of all, overheated homes can become deadly when heat waves strike. In the 2003 European heat wave more than 70,000 people died. A study into deaths in Paris during the heat wave found that people living in flats directly underneath the roof—typically the warmest spot in a building—were more likely to die than those living elsewhere.
In 2022, a report examined just how susceptible UK houses are to overheating. Commissioned by the Climate Change Committee (CCC), a public body that advises the UK government, the report found that 55 percent of UK homes already have bedrooms that overheat in hot weather. In a world heated by 2 degrees Celsius, the modeling projected that every home outside of Scotland would have unacceptably warm bedrooms, and 17 percent of homes—mostly in London—would have living areas and bedrooms that were too warm. If the world warmed by 4 degrees Celsius, every single home would meet criteria for overheating. With current policies and action, the planet is currently heading toward around 2.7 degrees Celsius of warming.
“The most at-risk buildings and homes tend to be smaller,” says Michael Edwards, a director at the architectural firm Arup, which wrote the CCC report. Stopping overheating in all UK homes in the current climate would cost £250 billion ($319 billion) in building upgrades, although Edwards points out that an efficient way to spread the cost would be to upgrade the buildings while other changes were being made.
It’s a hefty total, but the anti-heat interventions needed are surprisingly modest. Fitting houses with external shutters and windows that block intense sunlight would be a good start. “The idea is to stop radiation, rather than dealing with it once it comes inside,” says Mavrogianni. External window shutters are common in Mediterranean countries like Spain, Italy, and Greece, which are used to dealing with intense summers. Shutters are even more effective when combined with fully openable windows—which is another thing that’s often lacking in London homes. Fitting residences with shutters, light-blocking windows, roof insulation, and ceiling fans would eliminate overheating everywhere except London, which would still have some overheating, according to the Arup report.
Air conditioning could help—but only as a last resort. Only around 5 percent of UK houses have air conditioning, and even Mediterranean homes are much less likely to have air conditioners than the average US home. In the Arup modeling, air conditioners would be needed in 22 percent of homes to cope with overheating in the 2 degrees of warming scenario. This comes with downsides. Air conditioners use a lot of energy, and they’re vulnerable to power failures—compounding problems in worst-case scenarios if electricity grids fail. “It’s important that we prioritize the passive cooling strategies,” says Mavrogianni.
Building regulations are also catching up with the risk of overheating. In 2021, the UK government updated guidelines for new homes in England. The update states that buildings should be constructed in a way that minimizes unwanted excess sunlight in the summer and allows easy ways to get rid of heat. It also sets maximum limits for window sizes as a proportion of floor space. Small apartments, in essence, should have smaller windows—unless there is particularly good ventilation.
Retrofitting buildings isn’t the only way to deal with heat. We can make urban spaces cooler by planting more trees, creating green spaces, and building shade structures. London has a cool spaces map that points out places in the city with below-average temperatures, as well as water fountains and indoor cool spaces where people can take refuge from the heat. Mavrogianni points out that a lot of knowledge about dealing with high temperatures is strongly linked to culture.
The best way to deal with home heat for most people is to open windows in the morning, allowing that cool air to circulate, and then close those windows and blinds during the sunniest hours of the day. Edwards points out that following this kind of behavior can lead to much cooler homes. In the Arup modeling, a “perfectly” behaved occupant would experience much less nighttime overheating compared to someone with less optimal behavior.
But not everyone is able to follow the optimal cooling strategies, or to retrofit their homes for lower temperatures. People who rent their homes might not be allowed to install blinds or ceiling fans, while poorer homeowners can’t necessarily foot the bill to retrofit their properties. And people who are most vulnerable to heat—older people and those with health conditions—often already live in the hottest housing. Even simple cooling strategies, like opening windows, don’t always survive contact with the real world. Urban noise and pollution can make people less likely to open their windows, which can make their homes more likely to overheat.
Of course, the best thing to do is reduce the need for cooler homes. That means trying to make sure we never reach heating scenarios of 2 degrees, 4 degrees, or even higher. A cooler planet will mean cooler homes. It’s as simple as that. As Viñoly, the designer of the car-melting skyscraper, pointed out, buildings are only part of the problem. “Now you have all these sunny days,” he told The Guardian. “So you should blame this thing on global warming too, right?”
