The population of Firminy, south-east France, has been dwindling for decades. Its recent history is one of factory closures in a region built by steel, and locals tell me that many people leave for better opportunities in neighbouring Saint-Étienne, or to live in the Haute-Loire’s countryside.

On the top of a hill, however, stands Firminy’s pride: l’Unité d’Habitation, an imposing tower of concrete designed by Le Corbusier. The architect’s final project is an oddity – a building for people, where two-thirds of the apartments are dedicated to habitations à loyer modéré (or HLM – social housing); but also a piece of history, whose facade and roof were listed as monuments historiques in 1993.

It was also designed for a 1960s climate, not the sweltering temperatures we have experienced for much of the summer. For its residents, the tower feels increasingly like an unlivable furnace – and because of its protected status, that is unlikely to change soon.

We are on the brink of the fourth heatwave of the year when I meet a group of residents at the bottom of l’Unité d’Habitation. They have had enough. Inside their flats, during a heatwave, the temperatures regularly reach 35C, and can rise to 40C.

“I slept on the floor because it was the only place I could stay cool,” says Aurélie Mohamed, who has lived in l’Unité d’Habitation for five years.

“I slept on the balcony,” says Nathalie Rouchouse, who moved in 15 years ago.

“My godmother was one of the original residents of Le Corbusier, and I can remember coming here aged nine,” Chantal Hospital tells me. “We marvelled at the building; we were so proud of it in Firminy. It’s been 26 years since I moved in, and now I’m doing my best to move out. I never want to live in a historic monument........

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