Warning: White Roofs Are Proving To Be Problematic In Our Climate Zone
Many experts agree that light-colored, reflective surfaces are most appropriate in warm southern climates while dark, heat-absorbing surfaces are best in the north.
In a report, Guidelines for Selecting Cool Roofs, July 2010, the U.S. Department of Energy makes the following observations:
- Climate has the biggest impact on energy savings. Cool roofs achieve the greatest cooling savings in hot climates (Climate Zones 1-3) but can increase energy costs in colder climates due to reduced beneficial winter time heat gains.
- When cool roofs are optional yet encouraged, the decision should be considered carefully as cool roofs do not perform equally well everywhere.
- The energy cost savings you can realize from a “cool”(white) depends on many factors, including where you live.
- Although annual cleaning can restore up to 90% of initial reflectance, the energy cost savings alone does not warrant the cost.
- As a cool roof becomes dirty from pollution, foot traffic, wind-deposited debris, ponded water, and mold or algae growth, its reflectance will decrease, leading to higher temperatures.
- There are some important questions about the durability of cool roof systems in certain applications.• In colder climates, like Chicago or Alaska (Climate Zones 5-8 in Figure 8), there is less heat available to dry out the roof and more opportunities for condensation to occur.
EPDM (ethylene propylene diene terpolymer) single-ply roofing membrane is the only roofing material that offers solutions for all climates without the need for additional coatings or modifications.
In 2008, Certified Energy Manager Randy Koller, P.E., conducted an energy analysis for the West Virginia School Building Authority using the Department of Energy (DOE) Cool Roof Calculator. He found that black roofs installed on the state’s public schools showed favorable results for potential energy costs and carbon emissions when compared to white roofs.
His analyses compared assemblies using dark-colored and white reflective membranes with R-values ranging from R-15 to R-32. The results of the study concluded that energy cost and carbon emission comparisons were conducted, and black roofs were found to be the most economical and environmentally friendly option.
Above: Carlisle Syntec, a manufacturer of black, and white, roof membranes advertise a map of the United States, transmitting the message,”you want to have a black roof anywhere in the blue zone”. In their advertisement are bar graphs created from data that was supplied by he U.S. Department of Energy’s Cool Roof Calculator.