If you think it doesn't matter all that much what color the roof should be, think again. There's a heated debate in the roofing industry as to whether dark roofs or light roofs are the best and most energy efficient for commercial buildings.
Ever since U.S. Energy Secretary Steven Chu announced in 2009 that global warming could be more efficiently combated by painting roofs and roadways white, roofers in the United States and Canada have been discussing the color of the roofs they install. The statistics he cited were part of a study done by Lawrence Berkeley National Laboratory that found most flat roofs only reflect 10 to 20 percent of sunlight.
Benefits of White Roofs
Not all roofs can help improve the energy efficiency of the buildings they cover. Skyscrapers in dense areas with small, pointed roofs will not see the same benefit as a large warehouse in a suburban location, for example. But for many buildings, white roofs could provide the following benefits:
- Cooler building temperatures. White roofs reflect between 60 and 80 percent of heat instead of absorbing it, so they will not require the same amount of energy for cooling and air conditioning.
- Reduced "heat island" effect. In areas where buildings are very close, like a city, one hot building can cause the others nearby to get warmer, too. A white roof leads to cooler temperatures for all the buildings in the area.
- Reflection of the sun's rays. This doesn't just impact the building; the theory is that the rays reflecting back into space help cool the atmosphere, too.
Disadvantages of Black Roofs
Besides absorbing more heat, black roofs may cause more fatalities overall.
A newer (2014) study from Lawrence Berkeley found that black roofs could actually cause health problems, because people who live on the top floor of buildings with dark roofs are more likely to have health problems or die during heat waves.
But this doesn't have enough of an impact to make roof color regulated by law, according to industry group EPDM Roofing Association. Members of the group believe that because the cooler climate areas would actually benefit from darker roofs, choosing the best roof color should be left up to roofing contractors and other professionals.
How Would White Roofs Work in Canada?
Canada has, on average, a cooler climate than the areas of the United States that were considered in the original Lawrence Berkeley study. One of the dissenting opinions about the value of white roofs comes from cooler climates, where heating buildings is much more important than cooling them. For example, the demand for heating buildings in Manitoba is 30 times more than the need to cool them.
Thus, white roofs in cooler areas of the world may actually require more energy to keep them heated than darker roofs. To determine which color of roof and what materials should be used in your area for sustainability and energy efficiency, talk to your roofing contractor for the best available options.