Whether the goal is to meet government mandates, save money on energy bills, take advantage of rebates, or help save the planet, homeowners and business owners are finding that cool roofs are an attractive option. Some architects and builders are specifying cool roofs in pursuit of LEED points; others are complying with local or regional mandates, typically for use in public buildings.
Building material suppliers who want to be a resource for their customers who are interested in cool roofs would do well to learn the language. The simplest explanation of cool roofs comes from California’s Consumer Energy Center, which defines them as roofs consisting of materials that “very effectively reflect the sun's energy from the roof surface.” They must also have high emissivity, allowing them to emit infrared energy. Cool roofs can reduce the roof surface temperature by up to 100 degrees F. This helps cut energy bills, reduce maintenance costs, and extend the life of the roof.
The availability of cool roofing materials has expanded dramatically in recent years; they go well beyond white protective coatings for flat roofs. Today, roofing manufacturers offer cool roof options in virtually every type of roofing material, and in all colors—even black. Colored coatings contain infrared reflecting pigments. The Cool Roof Rating Council, an independent organization that tests roofing materials, lists cool options for built-up roofing, foam roof systems, metal, modified bitumen, shingle, slate, tile, single-ply, and roof coatings.
“There are a lot of different products that might have cool characteristics,” says a manufacturer of composite slate materials. “It’s an evolving technology. Most people will think it’s a white product or single ply, but the pigments don’t have to be monotone or bland.”
According to the U.S. Department of Energy’s Guidelines for Selecting a Cool Roof, two key properties—solar reflectance and thermal emittance—determine a roof’s temperature. Each are measured on a scale of 0 to 1. The larger the values, the cooler the roof will remain in the sun.
The type of cool roofing used depends on the the pitch of the roof. According to the Department of Energy, thermoplastic membranes, elastomeric coatings, and metal roof products are appropriate for low-slope roofs (a pitch of 9.5 degrees or less). LEED requirements are stricter, defining a low-slope roof as having a pitch of 15 degrees or less. For steep roofs, cool asphalt shingles, clay tile, concrete tile, and metal products are available.
Counting the Cost
As with all building materials, costs for cool roofing products can vary tremendously depending on location. A study done at the Lawrence Berkeley National Laboratory noted a premium of about 20% for cool roofing materials; one roofing manufacturer said that its cool roof products are about 25% more expensive than conventional materials. However, long-term savings can offset the initial cost. A California study found an annual yearly net savings of nearly 50¢ per square foot. That took into account the price premium for the products and any increased heating costs in the winter, as well as savings from lower summer energy bills, the ability to downsize cooling equipment, and lower labor and material costs over time, since cool roofs don’t have to be replaced as often as conventional roofs.
Tax credits also are available for homeowners who want to upgrade their existing homes to cool roofs in 2013. The credit—10% of the cost of the material, up to $500—is available for metal roofs with pigmented coatings and asphalt roofs with cooling granules that meet Energy Star requirements. The credit can’t be taken for new construction and rental properties. Comprehensive information on products and tax credits is available at www.energystar.gov.
The Energy Department's cool roofing guide also offers a detailed cost comparison between cool and hot roofs. It maintains that installing a cool roof need not cost more than a conventional roof.
Since cool roofs reflect the sun’s heat, they reduce cooling costs in the summer, but they also can increase heating costs during the winter. The Department of Energy recommends cool roofs most strongly for Zones 1 through 3 of the nation’s eight climate zones. Those zones include most of the South, Southwest, and California. Its Roof Savings Calculator provides information to determine if the savings will be sufficient to justify the expense.
The Cool Roof Ratings Council points out that the increased winter heating costs usually are “greatly outweighed” by the savings in summer cooling costs. One manufacturer noted that “cool roofs can be beneficial in any area of the country, but that common sense tells us that the hotter parts of the country, especially the Southwest, are really a good target market for these products.”
Building material suppliers can be incredibly helpful partners to their builder and remodeler customers by aggregating the wide array of information—from research studies and material rating applications to local codes and rebate programs—that are available. The Environmental Protection Agency provides detailed information on cool roofs in its publication, “Reducing Urban Heat Islands: Compendium of Strategies.”
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