No matter how well a building is insulated, it will never reach maximum energy efficiency if the roof is allowed to absorb thermal heat. The roof's shape and materials and the direction in which the roof faces all play a part in how much heat the roof retains, but reflective roof paint can go a long way toward reducing the amount of the sun's heat that penetrates the roof and raises indoor temperatures. According to the U.S. Department of Energy, a simple coat of reflective paint can reduce the summer temperature of your roof by 50 degrees or more. (See References 3)
Reflective roof paint is similar to typical house paint, except the addition of polymeric binders gives it a thicker consistency that makes it form a thicker coating on the roof surface. You can apply reflective roof paint like regular paint, with a brush, roller or spray gun, and must use special primers to help it properly adhere to the roof material. Reflective roof paints are white, to reflect the highest amount of thermal energy possible. (See References 1)
Reflective roof paint can lower the indoor temperature of a building, limiting the need for air-conditioning in hot weather. When applied to entire blocks of buildings, like a shopping center, the reduction of thermal energy can be dramatic enough to lower the area's ambient air temperature. The heat reduction can also lessen the wear and tear on the roof's materials, extending the life of the roof. (See References 3)
The Roof Coating Manufacturers Association says that reflective paint can be applied to almost any roof material (see References 1), but the shape of the roof rather than the material determines whether reflective paint is your best option. The coating is generally used for flat or low-sloped roofs with minimal insulation (see References 2, page 1). Although the product may be applied to almost any roof, steep, well-insulated roofs may not see enough benefits to offset the cost. The roof must be in good repair; a coating of paint does not fix existing damage. Reflective paint is best suited for warm climates that use indoor cooling for most of the year, because the summer energy savings in cooler climates translate into solar heat loss in the winter.
The reflective paint itself is not the biggest expense of installation. The costs tend to climb if you have an older roof in need of repair before the paint can be applied. Labor is a cost factor as well if you hire out the work to a contractor. Energy savings and rebates can offset the costs of installation; visit the Cool Roof Rating Council website to see if "cool roof" rebates are offered in your area. Buildings with flat, dark roofs generally save more energy than newer, sloped or lighter roofs -- up to 67 percent, according to Washington State University (see References 2, page 2).