Building owners and managers with facilities in northern climates often believe that energy savings provided by a reflective roof in summer will be offset by heat loss in winter; that is, a building with a white roof will not “warm up” from the sun during winter months as it would with a black roof. However, several factors will minimize the potential wintertime heat gain from a dark roof:
- Hot air rises, so any wintertime heat transferred to the interior of a building from the rooftop will remain at the top, adding minimal warmth to the building or occupants.
- In all parts of North America, there are fewer wintertime hours of sunlight available to warm a building and affect energy costs (see chart, below). In fact, in some areas, there is a more than a six-hour difference between summer and winter daylight hours. Plus, the angle of the sun is less direct, which also minimizes warming potential.
- In many areas, roofs are covered with snow for much of the winter, turning them "white" and eliminating any potential black roof heat gain.
- Winter skies are typically cloudier than summer skies, which reduces the amount of sunlight that hits the rooftop even more. Sunnier summer days provide more direct sunlight on the rooftop, where a cool roof system can help reduce building energy consumption.
- The energy required to air condition a building in the summer is usually considerably more 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.
Once summer rolls around, white roofing systems offer a number of high-reflectivity advantages over dark systems: reflecting up to 87% of the sun’s energy that otherwise would be transferred to the building; improving the operational efficiency of rooftop HVAC units; and helping preserve the R-value of insulation by keeping destructive UV and IR radiation from penetrating the membrane.
Of course, the primary reason to install a new roof is to make your building watertight; high reflectivity is a “bonus” that can’t be obtained by dark, non-reflective systems. If you’re in the market for a new commercial roof, give Royalty a call. We’re experienced and well-versed in all aspects of commercial roofing systems that will protect your workers and contents from the elements – in every season.