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White roofs, an effective response to reduce urban heat

Groupe

13/01/2025

Every summer, millions of city dwellers struggle with heat waves that seem to get worse year after year. As the construction industry seeks to address both the causes and the symptoms of global warming, an ancestral technique – well-known from the sunny shores of Greece to the villages of Andalusia – is gaining new popularity. Applying reflective paint or a clear coating to roofs reduces the temperature of buildings and cuts air-conditioning costs by up to 30%. But how does it work ?

Cooling our cities with the albedo effect

White roofs are a simple application of the albedo effect: the ability of a surface to reflect sunlight. Unlike conventional, darker roofs, which absorb heat, white roofs reflect most of the sun’s radiation, reducing the temperature of their surfaces and of the building interiors. In summer, white roofs can reduce outdoor temperatures by 2 to 5°C, particularly in dense urban areas that become so-called heat islands.

Saving energy and reducing emissions: the magic of white roofs

White roofs shield buildings from solar radiation, thereby reducing the need for air conditioning and improving occupants’ comfort in the summer. However, the energy savings claimed by most suppliers of these materials should be treated with some caution. Indeed, while white roofs significantly reduce solar heat in the summer, the same process slightly increases heating consumption in the winter. It may not always be the case that a white roof decreases total annual energy use – especially in non-air-conditioned buildings !

Comfort, savings and social fairness

While the effect of a white roof on a building’s energy use evens out over the year, it does have a positive environmental impact. By reducing the urban heat island effect, reflective roofing helps to lower ambient temperatures in large cities, improving comfort and quality of life. From a social perspective, it reduces inequalities by offering a simple, inexpensive solution for people in developing countries, who are often the most vulnerable to heat waves.

Getting your roof white

Installing a white roof is simple and accessible – even on an existing building. It requires the application of special white paint or reflective membranes. These materials are durable, weather-resistant and able to retain their reflective properties for years. Many governments around the world support the practice with grants and tax credits to encourage property owners to adopt this environmentally-friendly solution.

White roofs are a simple and effective solution for combating urban heat and reducing summer discomfort in buildings. By reflecting much of the sun’s radiation, they significantly lower the temperature of buildings and help address global warming. As we struggle with climate change, this approach could become generalised in the cities of the future. Repainting roofs is not a miracle solution and it will not suffice to eliminate heat islands, but it helps mitigate them. It needs to be deployed alongside complementary approaches, such as planting more trees to provide shade, making the ground more permeable – with more exposed soil and less asphalt – and looking at how cities are ventilated to avoid obstructing the flow of air in urban areas.

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