On a recent morning during another week of high temperatures, a sweltering heat was building up on London’s streets. But a cool breeze wafted through Caz Facey’s three-bedroom apartment.

There was no air-conditioning, or even a fan. Instead, an awning over the living room balcony and a Virginia creeper climbing over the kitchen window provided shade, while the apartment’s layout had been revamped to create a cross draft, helping make a comfortable indoor climate even as millions of other homes were baking in a British heat wave, with temperatures hitting 33 degrees Celsius, or 91 degrees Fahrenheit, in some areas.

“There’s nothing kind of scientific,” Ms. Facey said. “It’s all kind of natural stuff.”

Though temperatures have eased off, Britain has had a hot summer, enduring at least four heat waves, and scientists say that such periods are generally becoming hotter, more frequent and longer. As the country adapts to this new reality, residents need to learn to live in homes that were built to retain heat in what had usually been a rainy, more temperate zone.

Some, like Ms. Facey, have been redoing their homes in innovative ways to keep them cooler. But for many people living in both aging houses and modern apartment buildings, it will require expensive and complex upgrades, architects and other experts say.

Common cooling strategies, like using curtains to block out sunlight, are not long-term solutions, these experts say. Neither was an experiment to smear Greek yogurt on the outside of windows to keep the heat out, as one researcher did.

The tried-and-tested method in hotter climates, air-conditioning, is widely considered a luxury, with portable units that would cool a single room typically costing from $500 to $1,000 — and with electricity prices in Britain much higher than in other parts of Europe and the United States. And, if those units run on electricity generated from fossil fuels, they are actually contributing to climate change.