Saving 30% in air conditioning costs thanks to cool roofing 

Whitewashed houses remind one of the striking beauty of the Cyclades in Greece. White lime was not chosen randomly. Its purpose was to reflect the sun’s UV rays and cool the inside of the homes. “Everyone knows that a light color absorbs less heat than a dark color,” says Antoine Horellou. “We didn’t invent anything! The idea with cool roofing,” continues the CEO of Cool Roof France, “is to reduce heating of a building roof thanks to the reflectiveness of its coating. It thus becomes cooler than the ambient air. This is why we chose the name ‘cool roof.’ The resulting decrease in air conditioning needs can represent up to 30% of the energy bill. And for areas not air conditioned, the comfort of the interior is of course improved.”

The solution is so effective that the Intergovernmental Panel on Climate Change considers it “one of the fastest and least expensive ways to slow global warming.” The IPCC has calculated that “painting roofs white would save 1 Gt/year of greenhouse gas emissions, the equivalent of 250 million vehicles worldwide!” There is an urgent need to take action, as 2019 is turning out to be one of the hottest years on record. This summer, Paris experienced unprecedented high temperatures, with 42.6°C (108.7°F) recorded on July 25.

In France, the Cool Roof company was established in 2015, by three entrepreneurs convinced of the effectiveness of cool roofing after having carefully observed New York’s example. That very year, the start-up from Brittany landed its first deal in Quimper, covering the 7,000 m² (75,347 ft²) surface of a Leclerc shopping center. “Our client wanted to reduce its energy consumption, in particular from air conditioning, and limit heat in the hypermarket. The data collected indicated a 15% reduction in the building’s energy consumption, equal to nearly 4 metric tons of CO2 equivalent per year, and annual savings of €20,000 on energy. Other benefits include decreased maintenance costs and a longer roof life.” Since then, some fifty clients have solicited the company’s services. They include the Boulanger shopping center in Amiens, the 2G terminal at the Roissy-Charles-de-Gaulle Airport in Paris, the fire station of Paris in Villeneuve-Saint-Georges, the Berlemont gymnasium, and the Adamant floating hospital, also in Paris.

In 2018, Cool Roof France completed the largest reflective roof in France on the Géant Casino of Valence-Sud, with 18,000 m² (193,750 ft²) painted white. This building, too, has had impressive results: the hypermarket recorded temperatures up to 36°C (96.8°F) lower on the roof after treatment and has seen a drop of 12% in its overall energy bill! Encouraged by this success, the Casino group launched a bidding process for the deployment of cool roofing on other buildings suffering from problems caused by high temperatures.

Cool roofing can also be used to avoid investing in costly air conditioning. Aximum, another company providing cool roof paints and a subsidiary of the Colas group, completed a project in Oise on an R&D site of Bostik, which manufactures glues and adhesives. As Jean-Baptiste Izart from Aximum explains, “this reflective coating applied to 1,000 m² (10,764 ft²) limits the impact of solar rays on the facilities and improves thermal comfort in the summer, since we are in a building without air conditioning. The first measurements indicated temperatures lower than 25°C (77°F) on average in August, with peaks at greater than 30°C (86°F). The following summer, after the application of the white paint, we had almost no days when the inside temperature exceeded 25°C!” the expert from Aximum shared with us.

Another example is the Louis Blanc school in the 10th arrondissement of Paris, where Cool Roof France installed a white roof. The measurements taken measured the average variation in inside temperature, comparing a “cool roof classroom” to its conventional neighbor. The result showed less than 6°C (42.8°F) of difference and the elimination of periods of discomfort in the summer (above 28°C [82.4°F]).

The Brest-based company is making use of its clients’ empirical data to educate prospective clients: “To prove that it works, we have instrumented cool roofs using heat sensors and air conditioning consumption control.” There is still more educating to be done. “We often go about doing things the wrong way. You’re at the beach and you’re hot. You’re not going to start by putting an air conditioner next to yourself. You’re going to start by moving into the shade! The same goes for a building. You have to start by addressing the source of heat, in this case solar radiation. The solution of air conditioning is nearly systematically selected since people think it has a bigger direct impact. It isn’t always appropriate. We help our clients perform energy assessments in their buildings and hope to show them that cool roof technology contributes significantly to improving them. We’re developing energy intelligence!”