White paint, a shield against heatwaves?

By reflecting the sun's radiation, light colors avoid storing heat in the building envelope. The apostles of this solution readily cite, as ancestral examples, the famous white villages of the Cyclades or Andalusia.

“This is one of the solutions recommended today, because it makes it possible to respond to the impact of solar radiation on surfaces which will reflect this radiation instead of capturing heat,” explains Christine Leconte to AFP, President of the National Council of the Order of Architects.

“There is not a single solution to reduce heat in the city,” she adds, however. “To respond to the impact of the heatwave on buildings, we must open up a range of solutions that adapt to different contexts, including very heritage ones.”

For housing, the most important measures consist of protecting windows from solar radiation... and rethinking urban planning more broadly by creating more green spaces in the city.

“We are not making the white roof a miracle solution, but we are starting to integrate it into our public policies,” confides Margot Belair, town planning assistant at Grenoble town hall, where this process, applied to the roof of an old factory transformed into a third place, made it possible to lower the temperature inside and around.

“It has to be part of a whole bunch of tools to refresh the city: greening, refreshing the city on the ground with lighter coverings, de-waterproofing…” adds the elected environmentalist.

Energy savings

The white roof solution is especially popular for tertiary buildings, says Arthur Gilardi, sales director of ARKsolutions, a Toulouse SME.

“We have people who need comfort because they can no longer work in their warehouses and do not have an air conditioning system,” he says.

“And the second reason is energy savings. Since you are cooling your building, you are air conditioning less and we can talk about a 40% saving on air conditioning,” assures Arthur Gilardi.

For Pierre Elin of ThermaCote "before carrying out insulation work, you must start by analyzing the needs and determining which part of the home is most subject to 'attacks' from heat or cold. On houses In residential buildings, industrial or logistics sites, it is the roof that is most exposed to heat. And on residential buildings it is rather the facades. Good insulation and therefore good cost control will depend on the good analysis. energy. Thanks to the performance of good insulation, the reduction in temperature can reach 20° and a roof or facade can go from 60° to 38°, even with a dark color in the case of a zinc roof with a coating like ThermaCote".

Working on large buildings also allows you to be more efficient, testifies Julien Martin-Cocher, deputy general manager of Cool Roof France, a pioneering company in reflective painting.

“When I do 10.000 square meters, the equivalent of a Stade de France, on a commercial surface, it will take me a week. If I did it on 100 houses of 100 square meters each, it will take me three months. "

Tertiary buildings, moreover, often have roofs that are too weak to apply other solutions such as greening.

Doubts nevertheless remain about the effectiveness of these paints developed for their refreshing effect, points out Stéphane Hameury, operational director "building envelope" at the Scientific and Technical Building Center (CSTB).

“Beware of risks”

“It is not completely proven today, with the expected scientific robustness,” he says.

“The benefit, if it is proven, is more for the inhabitants on the top floor. Hence the interest in using it rather for the roofs of logistics buildings”, which are large and low.

There also arises, continues Mr. Hameury, "the question of the sustainability of these systems. To maintain their capacity, they must remain white."

He is also concerned that the paints could have undesirable effects on the materials they cover. “Be careful of the risks a posteriori. We must undertake a rigorous evaluation of these systems, something which is not done today.”

Finally, the use of white paint on facades or floors can be unpleasant to the eye by having dazzling effects.

In Lyon, where the metropolis had tested the installation of anti-heat paint on a sidewalk, the experiment will not be replicated because "this product tested on public roads ultimately did not correspond to our needs and our uses", communicates the community.

“The use of white paint, for facades and roofs, is one of the solutions identified and it will be part of a global action plan,” she promises, however.

Illustrative image of the article via Depositphotos.com.