Power of reflection
From sunny San Diego to frigid New York, roofs across America are slowly becoming whiter, brighter — cooler.
Most traditional dark-colored roofs absorb 70% or more of the solar energy striking them, resulting in peak roof temperatures of 150-190 F. By comparison, white, reflective roofs are 50-60 F cooler on hot days. That can decrease cooling costs by 15-20% on average, depending on the type, size, and location of a building (See sidebar, opposite).
Five years ago, it was this prospect of significant savings in cooling costs that aroused owners' interest in white roofs.
Today, the specification of cool roofs is being driven by stricter energy codes, government incentives, and the industry's shift toward energy efficiency and sustainable design.
André Desjarlais, program manager with the Building Envelopes Program for the DOE's Oak Ridge (Tenn.) National Laboratory, lists three reasons why cool roofs are being encouraged in many regions of the country: energy savings, reduction in the urban heat island effect, and reduction in peak energy demand.
Last September, for instance, Chicago implemented its Energy Conservation Code to reduce its urban heat island effect — the amount of solar energy absorbed by buildings and transmitted to the atmosphere. The code requires the installation by 2008 of roofs on new buildings, renovations, and additions that meet or exceed minimum criteria to qualify for the EPA's Energy Star program. Energy Star requires that low-slope roofs have an initial solar reflectance of 0.65 or greater. Steep-slope roofs must have a reflectance of 0.25.
"The Chicago requirement is not an energy requirement, it is strictly an urban heat island requirement," says Desjarlais. A major impetus for the code change was the heat wave in 1995 that killed 525 mostly elderly people.
Desjarlais says that energy savings from cool roofs for buildings in cooler climates may be minimal — or none at all — if air-conditioning is not run enough days. In some cases, building owners may actually pay more in heating costs with a white roof, because dark roofs absorb heat.
Reducing peak energy demand is a major concern for many power companies, and some utilities — including companies located in cooler climates, like Minneapolis — now offer rebates to building owners that install cool roofs. This can be misleading to owners of buildings in cool climates who think a white roof will provide significant savings in cooling costs, says Desjarlais.
"I think people are getting the false signal that since the utility is giving a credit to install white roofs, there has to be an energy savings," he says. "The utilities basically have one interest, and that's to reduce peak energy demand. Most people don't use electricity to heat, so that's not the utility's problem. They only want to make sure there's enough electricity for the AC in the summer."
Cool code comin' to California
In 1995, Georgia became the first state to include roof solar reflectance values in its energy code. The code allows Building Teams to reduce insulation requirements when a reflective roof is used. Now, other states, including California and Florida, are following in Georgia's footsteps with even more stringent codes.
California is currently amending its Title 24 energy code to "strongly encourage" Building Teams to install cool roofs. The proposed changes, which are expected to be adopted by the state's Energy Commission by July 1, 2003 and would take effect January 2005, would set a higher standard for cool roofing — "a bit higher than Energy Star at a 0.7 range for reflectivity," says Peter Turnbull, chairman of the Cool Roof Rating Council (CRRC), Washington, D.C.
"The way it will work is that if you put on a poor performing roof, you will have to make up that energy loss somewhere else in the building," says Turnbull. "Since at the time of new construction there is very little incremental cost for installing a cool roof, if the architect is faced with making the windows smaller or redesigning the lighting system or putting on a cool roof, they'll probably put the cool roof on."
Turnbull says the code will require Building Teams to select products rated by the CRRC. Like Energy Star, CRRC rates the solar reflectance and other cool properties of roofing materials. CRRC, however, conducts independent testing to establish its ratings, while Energy Star relies on manufacturers' data. So far, the CRRC database includes approximately 50 products.
Desjarlais predicts that most states with cool-load climates will adopt similar codes in the near future. He says that any states that adopt ASHRAE's 90.1 energy code, which offers credits for cool roofs, should see growth in white roofs.
California is also one of several states to offer incentive programs to promote the specification of cool roofs, as well as other "green" building concepts. Its Cool Savings with Cool Roofs Program is a state-funded initiative that provides rebates of 15-25 cents per sq. ft. to local governments, businesses, schools, and other entities that install cool roofs on new or existing buildings. Turnbull says that the utilities are planning to take over the program from the state to encourage owners to lower the amount of energy consumed during peak hours.
Similarly, New York's Green Building Initiative is ushering in the specification of white roofs in a more indirect way. The program provides tax credits to building owners that follow "green" design standards set forth by the state. Craig Kneeland, project manager with the New York State Energy Research and Development Authority, says the initiative does not recommend any particular building material, such as the use of white roofs, but rather sets energy-performance guidelines. Nonetheless, white roofs will no doubt be high on the list for owners looking to apply for tax rebates.
Also LEEDing the way
The desire by more owners to go for U.S. Green Building Council LEED certification is also a factor in the growth of white roofs, says John Thompson, principal with architect Zimmer Gunsul Frasca Partnership, Portland, Ore. Thompson is currently leading the design team on a 407,500-sq.-ft. expansion of the Oregon Convention Center in Portland, scheduled to open April 17.
The massive addition will double the size of the existing facility and will be covered by white thermoplastic polyolefin roofing membrane, commonly known as TPO. Although the building is in the northern climate, the white roof is expected to result in significant savings in cooling costs.
"This kind of building, with its large size and occupancy requirements, tends to need to cool almost the whole year through," he says. "You very rarely heat these kinds of spaces, because of all the people, equipment, displays, and lights."
The Building Team has already applied for certification as an Earth Advantage building by Portland General Electric, which means that it will exceed the state's energy code requirements by at least 20%. Thompson says the city is looking into applying for USGBC's new LEED-Existing Building program, since it is an addition.
Building Teams accustomed to specifying only traditional roofing should get to know cool roofs, because sooner or later, a local building code just might stipulate the installation of such a system in one of your projects.