Living in a sweltering, seventh-floor flat on a concrete housing estate south of Paris, Samira said she was feeling desperate as France experienced its highest temperatures on record this week. “Yesterday I sat down and cried, I thought I’m going to die,” said the 35-year-old single parent and former building caretaker.

Her flat in Ris-Orangis in Essonne is, like millions of apartments in France, poorly insulated and lacking in outside window shutters. “Blazing sun hits my windows all day – I can’t breathe, I feel dizzy, there is no air,” she said.

“My home is an oven, it’s unbearable. I can only use a fan for short bursts, for fear of electricity costs. I only get two hours’ sleep a night. I’m exhausted. The days feel endless trying to protect my son from the heat. And I know these temperatures are only going to get worse in time. The government only ever acts at the last minute. Not enough is being done long-term to protect people.”

Samira’s 10-year-old son, Issam, attends one of the 1,800 schools in France that have been closed because they are dangerously hot.

“My classroom on the top floor reached 40 degrees inside,” he said. “It was too hot to have lessons, so we just played games.” He normally goes to bed at 9pm but he has been up until midnight because it’s only manageable to be outside very late or very early. Samira said: “I feel shut in, physically and mentally.”

More than 44 million people in France, out of a total population of 67 million, have been under the highest red alert for heat this week, with daytime temperatures exceeding 40C in many places and staying dangerously hot at night.

The extreme heat has led to higher air pollution, a rise in hospital admissions, school closures and train cancellations. It has caused power cuts to thousands of homes from Brittany to the south-east, leaving people unable to ventilate their homes with electric fans or close electric blinds. French nuclear energy output was reduced as high temperatures limited access to cooling water. Hundreds of thousands of ⁠poultry have perished in the heat, overwhelming carcass collection services.

The impact of the heatwave has been made considerably worse by the high proportion of French buildings and infrastructure not designed to cope with high temperatures. Paris, one of Europe’s most densely populated cities, known for its poorly insulated housing stock, has for years been considered to have the highest heatwave mortality risk of any capital on the continent. The French government has been criticised for a lack of preparation and for cutting funding for projects designed to adapt infrastructure to the climate crisis.

Half of all French homes have insufficient protection from high temperatures, leaving inhabitants dangerously overheated, a report for the NGO Fondation pour le Logement (Foundation for Housing) found this month. About 66% of French people struggle to tolerate the heat in their homes.

Maïder Olivier, the head of climate advocacy at the NGO, said France had a “massive and worsening problem of heat-trap housing”. She said climate inequality in France was growing, with low-income, suburban housing estates suffering the worst from heatwaves.

“One of the aggravating factors is having no possibility of escape,” she said. Many residents on heavily concreted estates had a lack of green space around their homes, often worked jobs in high temperatures without air conditioning, had to travel on crowded, hot buses and could not afford to leave on holiday in the summer.

In Grigny, one of the poorest towns in the greater Paris area, Aboubakar, 60, who once worked in a hotel kitchen, wept as he stood below his fourth-floor flat, which he felt could reach 40C inside. “I’m suffocating,” he said. “I can’t afford to buy a fan. There are no shutters on my flat. At night I can’t sleep, it’s like a furnace.”

He said the heatwave had affected his mental health: other problems, such as his illness and housing insecurity, felt much worse in the heat. “It’s impossible to be inside my flat during the day so I come down and sit under a tree,” he said.

Roland, 20, a student doing a youth work apprenticeship, had woken at 7am to have breakfast with his girlfriend on a bench under some trees before the temperatures rose too high to be outside. “We try to close the shutters and stay in the dark in our flat but there’s no air,” he said. “It can be depressing. We only dare open a window in the middle of the night. We don’t use electric fans because it costs too much.”

Inès Seddiki, the founder of the organisation Ghett’up in Seine-Saint-Denis north of Paris, said young people from suburban housing estates were particularly suffering in the extreme heat. “They are not causing the climate crisis but they are the least protected from its consequences,” she said. “There is a lack of medical facilities in their areas for health support, their homes are heat traps, and the heatwave has exposed the racism in our society against them.”

She said when young people from the banlieue left their areas to try to seek respite, for example at the seaside, “some French commentators talk about an ‘invasion’ because it is a group of 15-20 young people who are Black or north African”. She said the heatwave had revealed the “inequality and segregation in French society”.

Several towns in the richest area west of Paris, including Neuilly-sur-Seine, this week banned access to their municipal swimming pool for anyone coming from other towns.

Noah, 22, on her way to a communications apprenticeship near Grigny, lives, like many students, in a small, top-floor flatshare in Paris, under a badly insulated zinc roof, with no shutters on the windows. She said: “There’s no air, we can never sleep more than four hours. We have tiny balcony space so we’ve put a children’s paddling pool on it and sit in there. What else can we do?”