Many parts in Canada face multiple threats that derive from the expansion of cities and urban environments. The main threat, which is a global issue is brought about increased energy use. Increased consumption of energy poses factors such as lesser air quality and the endangerment of human health and wildlife. A contributor to the rise in energy use are dark impervious surfaces that are laid out across cities in the form of paved roads and asphalt roofs. These surfaces absorb and radiate heat back into the surrounding atmosphere at a far greater rate than the natural landscape does, causing a heat island effect that raises ambient air temperatures in developed areas. This results in additional energy use for building cooling. Cool roofs offer the potential to address the urban heat island effect and improve the sustainability of urban areas all across North America.
Cool roofs use reflective materials, often but not always light coloured, to reflect more of the sun’s energy than traditional dark roofs, and to more efficiently transmit heat from the building’s interior. Compared to conventional dark roofs, the surface of a cool roof can be 28° to 33°C (50° to 60°F) cooler on a hot, sunny day. Studies have found that cool roofs can produce a similar savings in building cooling energy demand as green roofs.
Cities such as Toronto provide guidance and incentives such as the “Eco-Roof Incentive Program” for residential and commercial private party installations of green roofs and cool roofs to increase their use in our communities.
Environmental Benefits
Reduced Local Air Temperature
Citywide installation of cool roofs can actually lower the average city surface temperature and cool the outside air. Not only will the city feel more comfortable in the summer, we’ll be saving a lot of cooling energy.
Improved Air Quality
Reducing energy use in your home or office directly reduces air pollution from power-plant emissions. Reduced energy demand leads to reduced burning of fossil fuels, so in this way, cool roofs contribute to fewer emissions of air pollutants, such as carbon dioxide (CO2).
Higher temperatures increase the formation of smog in the air, making it dangerous to be outside. Cooling the outside air with cool roofs can slow the formation of smog.
Cool roofs not only cool your home, office or building, they cool the world. Cool roofs increase the earth’s reflectivity (known as its albedo), which in turn cools the planet. Replacing a hot roof with a cool roof immediately reduces the flow of radiant heat from the earth into the troposphere, the layer of the atmosphere in which we live.
Increased Global Cooling
Substituting 1000 ft2 (93 m2) of cool white roofing for standard grey roofing provides a one-time offset of about 10 metric tons of CO2, worth $250 (at a price of $25 per ton of CO2). Similarly, substituting 1000 ft2 (93 m2) of cool colour roofing for standard colour roofing provides a one-time offset of about 5 metric tons of CO2, worth $125. While the roof must be kept cool to retain this benefit, the offsets are based on aged, rather than initial values of solar reflectance.
