Energy-Efficient Roofing Systems

Energy-efficient roofing materials can dramatically reduce household energy use, thereby decreasing greenhouse gas emissions and significantly lowering utility bills. Though the initial price of an energy-efficient roof can be slightly higher, the investment is made up for in reduced utility bills over the life of the building. Many Energy Star-rated roofs are also eligible for tax credits. (See References 1)

Cool Roofs

"Cool roofs" is an umbrella term for several different roofing systems. In short, a cool roof is a roof designed to reflect sunlight and heat. Conventional roofing materials reflect only 5 to 15 percent, which means they absorb 85 to 95 percent of the energy and heat from the sun. The coolest roofing materials reflect more than 65 percent, absorbing 35 percent or less of the energy from the sun. Thermal emittance determines how readily a surface gives up heat. Ideally, a roof will have a high percentage of reflectance and a high percentage of emittance. (See References 2, page 3)

Low-Sloped Roofs

Low-sloped roofs are normally found on commercial buildings, industrial buildings and multifamily homes. They can be made more efficient through the application of cool coating or single-ply membrane. Cool coating is the consistency of thick paint and can be applied to existing surfaces, such as asphalt, gravel, metal and various single-ply materials. Cool coatings have additional benefits, including improved adhesion, durability, suppression of algae growth and an ability to self-wash under normal rainfall. Single-ply membranes come in prefabricated sheets and are generally glued or mechanically fastened in place over the entire surface of the roof. (See References 2, pages 5-6)

Steep-Sloped Roofs

Steep-sloped roofs are generally found on residential homes. The most common types of cool roofing systems for steep-sloped roofs include tiles and painted metal. Typical tiles, made of clay or concrete, reflect only 10 to 30 percent. "Cool-colored" tiles contain pigments that reflect 25 to 70 percent of solar energy, depending upon the color. Cool-colored metal roofing also contains pigments that reflect 20 to 90 percent. Metal roofing is more common than tile, as it is highly durable. (See References 2, page 7)

Heat Islands

Heat islands are urban areas that are hotter than nearby rural areas. A city with 1 million people or more can be 1.8 to 5.4 F warmer than its surroundings. Heat islands affect community-wide energy demands, air-conditioning costs, air pollution, greenhouse gas emissions and water quality. Cool roofs play a vital role in reducing the environmental and economic impact of large cities. (See References 3)

Green Roofs

Although green roofs fall into their own category, they provide similar benefits as cool roofs. Green roofs are gardens or mini-ecosystems that cover an existing roof with the aid of special planters. The greenery essentially shades the roof, reducing heat transfer and thereby keeping the building cool. (See References 4, page 4) Green roofs also act as insulators in cold weather and have a host of other benefits, such as absorbing rainfall for better stormwater management, reducing air pollution and providing garden space in densely populated areas where parkland is rare. (See References 4, pages 5-10)

About the Author

Beth Berry


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