There are many misconceptions when it comes to the perceived benefits of black roofs compared with white roofs.
Those living in a northern climate may think that summertime energy savings realized with a white roof will be offset by the elimination of a beneficial heating gain that might occur with a black roof in the winter; that the heating benefit of a black roof is greater than the cooling benefit of a white roof. However, several factors make any potential wintertime heat gain from a black roof relatively immaterial:
- The laws of physics dictate that hot air will always rise. Thus, 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 heating benefits to occupants below.
- In all parts of North America in the winter, there are fewer hours of sunlight available to contribute to warm a building. In fact, in some areas, there is more than a six-hour difference between peak-summer and peak-winter sunlight. Plus, the angle of the sun is less direct, which also helps to minimize potential warming.
- In many areas, roofs are covered with snow for much of the winter, turning them “white,” and eliminating any potential black roof heat gain.
- The energy required to air condition a building in the summer is usually considerably greater than the energy to heat it in the winter, making the potential for summer energy cost savings much greater with a highly reflective white roof than winter savings with a heat absorbing black roof.