Something as simple as the colour of a building’s roof can have a real effect on carbon emissions and energy usage. Juan Carlos, founder of the White Roof Project, explains the benefits of white roofs and how they can offer a smart and sustainable alternative.
What is a white roof?
Millions of rooftops in North America are made of tar, which absorb an enormous amount of heat during the summer months. Covering black tar roofs with solar-reflective white coating immediately reduces temperatures inside and out.
A white roof or “cool roof” stays cooler and cuts down how much heat is transferred to the building below by reflecting the sun’s heat. While some prefer to work with white because it is a low cost solution, there are many other ‘cool roof’ colors out there that can be applied to a variety of rooftops.
On average, 55 per cent of cities are man-made surfaces. In New York City alone, 12 per cent of surfaces are rooftops. A white roof project is low cost and easy to implement. It can cut down on carbon emissions, relieve stress on the power grid, thereby reducing the risk of ‘brown outs’ caused by stress on the power grid. It saves millions in energy costs.
What are the benefits for a building owner?
The statistics speak for themselves: a roof covered with solar-reflective white paint reflects up to 90 per cent of sunlight, as opposed to the 20 per cent reflected by a traditional black roof.
On a 32 degrees Celsius day, a black roof can reach up to 82 degrees, while a white roof stays a cool 38 degrees Celsius. Summer cooling costs can therefore be reduced between 10 and 30 per cent.
Aside from energy savings, a white roof saves money on repairs. The elastomeric white paint used for white roofs prevents warping and cracking, which occurs when black roofs are overheated in the sun. White roofs can also extend the life of a building’s cooling equipment by decreasing use.
Are there still benefits of white roofs in the winter?
In the northern United States and Canada, one might think that a black roof would provide a winter heating benefit to building owners. However, several factors make any potential heat gain relatively immaterial. The laws of physics dictate that hot air will always rise. As a result, any heat that is transferred to the interior of a building structure from the outside will remain at the top of the structure, providing minimal heat savings.
There are fewer hours of sunlight to affect energy costs during North American winters. In some areas, there is a greater than a six-hour difference between peak-summer and peak-winter sunlight, meaning there is less sunlight available to contribute to a building’s potential warming. Additionally, when the angle of the sun is less direct it helps to minimize warming potential.
Generally, the energy that is required to air condition a building in the summer is considerably greater than the energy needed to heat it in the winter. The potential for summer energy cost savings are much greater with a highly reflective white roof than winter savings with a heat absorbing black roof.
Juan Carlos is a filmmaker and the founder of White Roof Project, a nonprofit organization that aims to curb climate change.