Lyon to Classify Overheated Homes as Unsanitary, a First in France
Lyon, July 16, 2026 – In a groundbreaking move, the city of Lyon is set to integrate indoor temperatures into its housing sanitation evaluations. This decision, announced by the City of Lyon, marks the first time in France that excessive heat could render a dwelling officially unsanitary, potentially obliging landlords to undertake significant cooling improvements.
Historically, a dwelling’s unsanitary status was determined by issues such as humidity, mold, lack of heating, poor ventilation, or the presence of lead. However, with the escalating climate crisis and more frequent heatwaves, the risk of overheating has emerged as a critical concern for public health.
The municipal hygiene service in Lyon will now include temperature assessments in its evaluations. Should an apartment reach heat levels that endanger the health of its occupants, the prefect could be petitioned to compel the property owner to carry out necessary works. This initiative positions Lyon at the forefront of addressing the health impacts of climate change on urban housing.
The ‘Thermal Kettle’ Phenomenon: A Widespread Issue in Lyon
This decision is underpinned by alarming statistics. The City of Lyon reports that 62% of homes in the city center are classified as “thermal kettles” – dwellings that severely accumulate heat during summer. This issue is particularly prevalent in older buildings, where stone structures, common in historic districts, retain heat for extended periods. Contributing factors also include apartments exposed to direct sunlight all day, windows lacking external sun protection, and highly mineralized streets that absorb and radiate high temperatures.
Until now, the focus has predominantly been on “thermal sieves” – poorly insulated homes that lose heat in winter. Now, the reverse effect is causing concern: homes that retain heat to such an extent that they become barely habitable for several days.
A National Problem with Legislative Implications
The issue of thermal kettles is gaining national traction. A study published on June 16, 2026, by Pouget Consultants – a research firm specializing in building energy performance – for IGNES (the alliance of industrial electrical and digital building solution providers), analyzed nearly 9 million energy performance diagnostics (DPEs). The study revealed that one in two homes is classified as a thermal kettle, and nine out of ten are inadequately adapted to high temperatures. The primary factor identified is the absence of external solar protection, such as shutters or blinds.
This concern is also making its way into the legislative arena. Several deputies have tabled a bill aimed at better protecting tenants. Proposed measures include making summer comfort indicators visible in real estate advertisements and simplifying the process for tenants to secure modifications aimed at reducing heat.
Challenges in Implementation: Heritage and Investment
The effectiveness of this new approach remains to be seen. While recognizing a dwelling as too hot is a crucial first step, resolving the problem presents significant challenges. In many older buildings, installing external shutters can conflict with heritage regulations. Furthermore, insulation works or window replacements often require the agreement of co-owners and substantial financial investment.
This pioneering initiative by Lyon underscores the growing urgency to adapt urban environments to the realities of climate change, balancing historical preservation with the health and well-being of residents.
