Light-colored roofs are often called cool roofs. A roof that meets U.S. government cool-roof standards has a light-colored surface that is highly reflective and emissive, according to the EnergyStar, which is a joint program of the Environmental Protection Agency and the U.S. Department of Energy. EnergyStar says emissivity concerns the ability to release absorbed heat easily. Combined together, these characteristics cool building interiors. Contractors can change existing roofs with dark surfaces into cool roofs by rolling or spraying a white, paint-like coating on the roof or by covering it with a tough, white membrane. Cool roofing isn't limited to white paints and membranes.
Colors and Materials
Some highly reflective, highly emissive roofing materials look like regular asphalt roofing only they are typically in lighter browns, greens and grays. Metal panels and shingles are available painted with cool-roof coatings in a broad array of colors. They are highly reflective and qualify for the EnergyStar label certifying them as cool roofing, but Energy Star says they are not the best emitters of energy. Yet on snowy winter days, it adds, the extra heat that metal roofing absorbs causes it to use less energy to keep houses warm.
Lighter on the Budget
In the winter, white roof coatings and membranes can develop pools of ice, "The New York Times" reports in an article about the U.S. Department of Energy's project to convert all its headquarter buildings to cool roofs. Nevertheless, the Energy Department estimates summer energy savings totaling thousands of dollars. Savings are greatest for cities with the most hot days per year, the FacilitiesNet website reports. For example, an EPA-funded study estimates that cool roofs could save Phoenix property owners $37 million annually.
Light-colored roofs also decrease air conditioning costs from 10 percent to 30 percent on hot days when air conditioning makes up to 40 percent of daily electricity use, the New York City Department of Buildings reports. This could translate to fewer power outages.
Cooling Off in NYC
One of the most ambitious projects nationwide to save energy costs and create a more environmentally friendly urban environment is the CoolRoofs program. As of 2008, New York City code required most new buildings to cover at least 75 percent of roofs with reflective, white coating or materials with a cool roof rating from EnergyStar.
Cities are 5 to 7 degrees hotter than suburban and rural areas on an average summer day, because urban areas have more dark surfaces, including roofs and pavement, The New York City Building Department reports. This is called the "urban heat island effect."