Cool roofs are the most common reflective surfaces that have a high solar reflectance and also a high thermal emittance. The reflectance is the ability of a material reflecting the sunlight and thermal emittance is the ability to radiate the absorbed energy.
There are cool cars that are able to reflect more sunlight that conventional dark cars, reducing the heat transmitted into the car’s interior. It helps decreasing the cost linked to air conditioning, fuel consumption etc. Therefore, there is a positive effect in the climate since they help to reduce the temperature in the Earth’surface.
If a cool roof is used in hot climates can offer advantages like energy building savings, help in mitigating the urban heat island effect and reduce air pollution and greenhouse gas emissions. A good maintenance of these materials is required because albedo degradation and soiling can produce a loss quality of the material and decrease the energy savings of the surface.
Thermoplastic membrane roofs in white colors are reflective. This means that they have the highest reflectance and emittance. These membranes can reflect up to 88% of the sunlight. On the other hand, uncoated roofs only reflect 17% of solar radiation. White roofs also have a higher emittance than uncoated roofs.
This means that uncoated roofs absorb more sunlight than coated roofs. Uncoated buildings are warmer inside and therefore, the energy bills are higher than in buildings with coated roofs.
A green roof is a roof of a building that is covered with vegetation planted over a waterproofing membrane (waterproofing consists on creating a building envelope which is a controlled environment). Green roof is another kind of cool roof but do not reflect as much sunlight as cool roofs. The reflectance of green roofs varies depending on the species planted. The range of reflectance of the solar radiation is between 30% and 50%. In addition, green roofs offer other benefits such as: