Reducing solar radiation with cool roofs
The presence of black bituminous membranes on roofs enhances this overheating effect. This microclimate weakens as we move away from less mineralised areas or when the coverings are lighter in colour.
How to reduce the thermal impact on the roof with high albedo coatings?
Reflect = refresh
Flat roofs are the walls of buildings most exposed to direct sunlight. As a consequence, they contribute directly to the heating of the exterior and thus, through their inertia, of the interior spaces.
The presence of black bituminous membranes on roofs increases the effect of overheating, as their reflectivity is low, which is highly favourable for UHI¹. However, the more the roof of the building reflects solar radiation, the more the amount of heat that penetrates indoors is reduced: this is a material with a high albedo (the reflectivity of the surface).
¹ Proceedings of the National Academy of Sciences. The future of the human climate gap. 2020
Solution: encouraging the reflective effect of ''cool roofs''
The closer a material is to a light colour, the more it reflects the sun's rays. This performance is measured in particular by the Solar Reflectance Index (SRI)². On roofs, the aim is to convert black surfaces into white surfaces with a high SRI value. By turning dark roofs white, which can be very hot in summer, they absorb less heat.
² Ministère de la Transition écologique, Cohésion des Territoires, Mer. RT-RE Building. What is the SRI? 2022
What is the temperature gain with a cool roof ³?
Choosing a cool roof reduces the impact of urban overheating by up to 50%.
In Marseille, with a 100% solar heat base, a dark roof emits 40% less heat into the city, while a white roof emits 17%, or 57% less heat. For a cool roof with an SRI of 80, the roof surface temperature does not exceed 50°C, while for a dark roof it is 72°C.
³ TIPPE study. Numerical characterization of the external surface temperature of a Cool Roof in a given climate.
SOPREMA solution with the best SRI
More information: photovoltaic parking shading systems
In addition to generating electricity, the presence of photovoltaic panels on the car park shade provides shade for vehicles and the road surface, limiting the heating of the walls and the environment.