As Temperatures Soar Above 40°C, France Is Rediscovering An Old Window-Painting Trick To Keep Homes Cool

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As an intense  grips much of Europe, many households in France are turning to an unexpectedly simple solution to keep their homes cool: painting the outside of their windows with a removable white chalk coating.

The practice has gained attention as France experiences one of its most severe heatwaves in recent history. According to France’s national weather service, Météo-France, the current heatwave began around June 17 and is expected to rank among the hottest ever recorded in the country. Temperatures have exceeded 40°C in many regions, with some areas forecast to reach 42°C or higher, while more than 90% of the country has been placed under heat alerts. Experts say the combination of extreme daytime temperatures and unusually warm nights has made the event particularly dangerous.

The prolonged heat has already forced school closures, disrupted transport, prompted emergency health warnings and placed enormous pressure on hospitals and emergency services. Authorities have also advised vulnerable residents to remain indoors during the hottest parts of the day as Europe continues to battle extreme temperatures linked to climate change.

Against this backdrop, many French homeowners are coating exterior window panes with a temporary mixture of chalk and water. The white coating reflects a significant portion of the sun’s rays before they pass through the glass, reducing the amount of heat entering buildings. Unlike curtains or blinds, which block sunlight only after it has entered through the window, the chalk coating helps stop heat from building up indoors in the first place.

The technique has been used for generations in parts of southern Europe but is enjoying renewed popularity as more people search for affordable ways to cope with rising temperatures without relying heavily on air conditioning. Experts say the method is inexpensive, environmentally friendly and easily washed away once cooler weather returns.

Scientists note that Europe is the fastest-warming continent, with temperatures increasing at more than twice the global average. As heatwaves become more frequent, longer and more intense, researchers say practical cooling measures—whether modern or traditional—will play an increasingly important role in helping communities adapt.

While chalk-coated windows may appear unusual, they reflect a growing shift toward simple climate adaptation strategies. For many families across France, the centuries-old technique has become a practical response to one of the country’s most challenging heatwaves, demonstrating how traditional knowledge can still offer effective solutions to modern climate extremes.