Why it is difficult to clearly classify apartments as "Bouilloire thermique"

Paris - 09.07.2026: In France, reports are increasing during recurring heat waves of apartments that become considerably hotter inside than the outdoor air and are at times barely habitable. These "Bouilloire thermique" cases, however, cannot yet be clearly captured. Studies, administrative data and tenant reports point to a widespread problem, but the criteria to officially classify an apartment as overheated are neither standardized nor available across the board.At the core of the deficit is the data basis. The summer comfort criterion introduced with the building regulations RE2020 works with a ...