Cool Roofs, Cool Research

In the deep freeze of winter, it may seem a bit odd to be talking about bringing the temperature of the city down, but for engineering professor Hashem Akbari, it’s more than a hot topic.

Akbari, who joined Concordia in June 2009 as Building, Civil and Environmental Professor and a future Hydro-Quebec Research Chair, is studying the urban heat island; the phenomenon whereby a metropolis is usually significantly warmer than its rural surroundings. In an attempt to address the energy used to cool cities around the world during hot weather, he’s developing light reflective materials for roofs and pavements.

This simple idea, says Akbari, can potentially delay the effects of global warming.
Here’s how: Generally, pavements and roofs in urban environments are dark and absorb 80 to 90% of sunlight; this, obviously, keeps heat in the city. Those same surfaces covered with his reflective materials (white for roofs, lighter colours for pavements) will absorb only 30 to 65%.

By decreasing absorption of roofs by 25% and pavements by 15%, the overall temperature of a city can be reduced by two to three degrees Celsius. Ipso facto, energy requirements for cooling during summer are reduced.

Together, pavements and roofs comprise over 60% of urban surfaces. Akbari states 10 sq m of white roof replacing a dark roof can offset one tonne of CO2. In other words, the temperature reduction due to radiation not being absorbed by the earth is equal to the increase in temperature caused by one tonne of CO2 in the atmosphere, effectively balancing any change