Newly constructed, energy-efficient homes across France are overheating during summer heatwaves, leading residents to label the dwellings as “bouilloires thermiques” or thermal kettles [1, 2].
This trend highlights a critical flaw in current building standards. While high levels of insulation are designed to reduce heating costs in winter, they are now trapping heat inside dwellings during the summer months [3, 5].
The issue has become acute during the recent heatwaves of this summer, which included a second exceptional heatwave within two months [2, 4]. Residents in both urban and suburban areas said that these homes are becoming uncomfortable or even uninhabitable as temperatures rise [1, 3].
Data on the scale of the problem vary. Some reports indicate that approximately one-third of apartments and houses rated DPE A or B for energy performance are thermal kettles [6]. Other estimates suggest a higher prevalence, with some claims stating that one out of two homes falls into this category [4].
Beyond the specific issue of high-efficiency "kettles," the broader housing stock remains vulnerable. One report suggests that nearly nine out of 10 dwellings across the country are unsuitable for extreme heat [4].
The phenomenon is driven by the disconnect between energy-efficiency ratings and summer comfort. Insulation that prevents heat from escaping in January also prevents it from leaving in July, creating a greenhouse effect inside the home [3, 5].
“Newly constructed, energy-efficient homes across France are overheating during summer heatwaves.”
The emergence of 'thermal kettles' suggests that the French government's focus on winter energy efficiency through the DPE rating system has created a secondary public health risk. As heatwaves become more frequent and intense, the lack of summer-specific thermal standards means that the most 'efficient' homes may actually be the most dangerous during a heat crisis.
