How Cool Is Your Roof?
- By Michael Fickes
- November 1st, 2001
The EPA is so cool. A couple years ago, the Environmental Protection Agency adopted a building concept called cool roofs and made it part of the Agency’s Energy Star program. According to the EPA Website, an Energy Star-qualified roof can reduce peak cooling demand by 10 percent to 15 percent.
While Energy Star roof specifications do not specify particular roofing products, the EPA expects that most roofs qualifying under the program will be metal, single-ply membrane, and roofs protected with specially formulated reflective coatings.
Cool roofs benefit building owners by reducing utility costs. But they also help protect the environment. Buildings that use less electricity for air conditioning require utilities to burn less fossil fuel and reduce air conditioning and fossil fuel emissions that can accumulate into problems ranging from smog to global warming. The EPA’s interest in cool roofs aims to stem these environmental problems.
According to the EPA, the energy savings from cool roofs depend on geographic location and climate, insulation levels inside the building, the type of roof used and the quality of maintenance. Optimum overall savings on cooling can reach as high as 50 percent, with some savings coming from the purchase of smaller and so cheaper air conditioning systems.
Buildings that benefit most from cool roofs start with high air conditioning costs, feature large roof surfaces and low levels of insulation, and reside in hot climates. But most buildings can probably gain some savings from the concept.
How does a cool roof work? Interestingly, it’s not the heat of the sun that heats up the roof. “The sun emits infrared radiation,” says Steven McGuinness, president of Advanced Coating Systems, Inc., in Atlanta, a manufacturer of roof coatings. “When this radiation strikes an object, the color of the object resists or reflects the radiation. Dark colors have more resistance. Light colors have less resistance and more reflectivity. The magic is in the color.”
Cool Metal Roofs
Darker colored metal roofs can also reflect infrared light.
“There is no set amount of reflectivity associated with the term cool roof,” says Todd Miller, president of Classic Products, Inc., a supplier of metal roofing products based in Piqua, Ohio. “But the EPA’s Energy Star program has developed a cool roof component for metal roofs. It requires a metal roof to reflect at least 25 percent of total ultraviolet light.”
“In addition, the EPA requires manufacturers to submit test data from roofs that are three years old and performing in a variety of climates to show that these roofs maintain their 25 percent reflectance,” says Miller.
According to Miller, metal roofs designed to achieve 25 percent reflectivity can generally maintain that level of reflectivity through three years, even with the dark colors characteristic of metal roofs.
“Bright, clean, white roofs provide high reflectivity,” Miller says. “But the percentage drops quickly when you get into darker colors. You can end up around seven percent to nine percent. We’ve developed a product that uses reflective pigments in a paint coating. Even in dark colors, we’re getting reflectivity rates from 25 percent to 35 percent,” which falls within the Energy Star requirements.
Classic Products purchases special paints mixed with these pigments to produce its cool, dark metal roofs.
Cool Single-Ply Roofs
Lighter colored roofs, and white roofs in particular, produce the highest levels of reflectivity. “The key to reflectivity is the white color,” says Paul Knox, manager of Engineering Services for Duro-Last Roofing, Inc., an Energy Star cool roof manufacturer based in Saginaw, Mich.
Duro-Last picked up on this concept early. The company has been manufacturing white, tan and gray colored single-ply, copolymer alloy poly-vinyl chloride (CPA-PVC) roofs since 1978. The formulation used to make Duro-Last’s CPA-PVC products creates a membrane that is a single color throughout. In other words, the color won’t wear off.
“Typically, our product will only heat up to a temperature 10 degrees higher than the ambient temperature,” Knox says. “If it’s 90 degrees outside, our membrane will heat up to 100 degrees.”
According to Knox, the EPA has set higher reflectivity requirements for white membrane roofs when it comes to Energy Star ratings. “Our membranes must have an initial reflectance of 60 percent,” he says. “After three years, the materials must retain a level of at least 50 percent.
White membranes seem capable of handling that. Most manufacturers of white membrane roofs start with a reflectivity of 75 percent to 80 percent, continues Knox. Duro-Last membranes reach reflectivity levels as high as 86 percent.
But who wants a white roof? “We’ve found that facility managers are moving toward white because of the high reflectivity,” Knox says. “I think you’ll see that white is becoming a trend.”
Cool Roof Coatings
“Before the Energy Star cool roof program, roof coating manufacturers typically sold coatings to stop leaks or extend the life of a roof,” says McGuinness of Advanced Coating Systems. “Since the Energy Star rating system appeared, the market has changed dramatically. We are becoming a retrofit solution to the problem of energy usage.”
Coatings start out as nontoxic, nonflammable, water-based liquids that may be rolled, brushed or sprayed onto roofs. When the material dries, it forms a rubberlike film with no seams. As a roof heats and expands, the coating moves with the roof deck, whatever the underlying roofing material. This feature makes coatings less susceptible to the effects of weather. White paint, for example, may crack and peal under the influence of temperature changes.
According to McGuinness, facility managers should investigate the difference between coatings and paints. “Paint, for example, goes on in a thickness of about 2 mils,” he says. “Our coatings are applied at 20 mils. So there is a considerable difference. In addition, a coating has a great deal of elasticity. It’s almost like a sheet of rubber.”
Unlike a sheet of rubber, however, it’s very cool.