Cool Roofs

DEFINITION & TYPES OF STRATEGIES

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.

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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.

COOL ROOFS VIDEO

There are measures to prevent the problems mentioned above:

  •  Reducing the extremes of temperature change will reduce the damage to the material of the surface.
  •  Using materials that reflect ultraviolet and infrared radiation will reduce damage caused by u/v and heat degradation.
  • White color reflects more than a black color. In addition, white colors control the problems related to the exposure of the sun.

Types of cool roofs

COOL ROOFING MATERIALS

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.

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GREEN 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:

  • Reduce heating by adding mass and thermal resistance value.
  • Reduce cooling (by evaporative cooling) loads on a building by 50% to 90%.
  • Create a wildlife habitat.
  • Reduce run off.
  • Filter pollutants and CO2 out of the air.

Benefits to the Environment

It is estimated that if all flat roofs in warm climates were cool roofs, there would be an increase of a 10% in global reflectivity. This would offset about 24 Gt of GHG. An unit-roof-area mean annual radiative forcing impact is -44,2W/m2.

4300 ha of cool roof in 10 years is comparable to remove around 1,76MMT of atmospheric CO2.

The adoption of cool roofs in urban areas by increasing albedo by 25% could achieve a lower total global radiative forcing of 0,044 W/m2 averaged over global land area.

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