Walls, roofs, cars: should everything be painted white to reduce the heat?

the essential
The color of the paint can vary the heat of the surfaces by several degrees. Faced with climate change, this economical solution is applicable to your homes and cars… in certain cases.

Painting the walls or roofs of dwellings in white, a color which rejects the sun’s rays, rather than black which absorbs heat, would make it possible to reduce the temperature effectively: a welcome alternative solution after a scorching summer in France and in the world.

The roofs

Painting your roof white can reduce the heat of a surface, especially depending on the materials that make it up: asbestos, concrete and metal greatly absorb heat, making white paint all the more efficient. The difference can reach 2 to 5 degrees inside buildings, and varies by several tens of degrees on the roof itself.

However, it is possible that the local urban plan (PLU), of your city lays down restrictions about maintaining your roof. Although this practice is rapidly becoming more popular, the best thing to do is to check with your town hall.

The walls

A white coating able to attenuate the heat.
Pexels – Diego Ramirez

As with roofs, walls benefit from a drop in temperature. Be careful though: it is the exposure of a surface to the sun that causes its temperature to vary. A little exposed wall repainted from white to black will therefore not lower the temperature significantly.

Purdue University in the United States was able to design a White paint able to repel 98% of the sun’s rays against 90% in normal times, and whose use can make it possible to do without fans and air conditioners in several cases.

Some cities, like Los Angeles, have thus taken the decision to repaint their surfaces and streets in white to avoid excessive temperatures; the municipality indicates a drop of between 5 and 7 degrees in temperature for the streets concerned. A Toulouse company offers a similar paint, which cools living spaces and lowers energy bills.

Cars

The results are less conclusive for cars. A white vehicle will logically store less heat than a car with darker colors. However, the real difference lies outside the cabin: the temperature inside the vehicle is mainly generated by the reflection of the sun by the windows. Thus, a car painted white will present a heat difference outside the vehicle, but its interior will remain stuffy, provided its windows are the same as a black car. To lower the temperature, it is therefore better to favor sun visors…

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