When re-roofing, choose an Energy Star-labeled roofing material with high solar reflectance. Solar reflectance is the percentage of the sun's energy reflected by the roof surface. Roofs with higher reflectance absorb less solar energy, keeping your home cooler and more comfortable in hot weather. They can reduce the need for air conditioning by 10–15% at peak times, and can reduce energy bills by as much as 50%, depending on climate. Because high temperatures are one of the factors that shorten the lifespan of roofing materials, cool roofs may last longer before needing replacement. Cool roofs also help lower the air temperature surrounding houses, which helps fight the "heat island effect"—increased air temperature (2 to 8 degrees Fahrenheit) in cities versus rural areas. Using less air conditioning and fighting the heat island effect directly decrease environmental pollution.
Energy Star-labeled roofing can reduce the temperature of a roof by as much as 100 degrees. The Energy Star criteria differ for low-slope (less than 2 inches of rise over a 12-inch span, or 2:12 inches) and high-slope (2:12 inches or greater) roofs. To qualify for the Energy Star label, a low-slope roofing material must offer an initial solar reflectance of at least 0.65 (on a scale of 0 to 1); high-slope roofing material must have an initial solar reflectance of at least 0.25.
Single-ply membranes and paint-on coatings can be used on both low-slope and high-slope roofs. Other common low-slope cool-roof materials are modified bitumen (asphalt), polyurethane foam, and standing-seam metal. Other common high-slope cool-roof materials are cement or ceramic tile, and metal shingles.
1. Measure to determine the slope of your roof.
2. Research local regulations for materials and installation methods.
3. Choose the highest-reflectance material available, factoring in slope and regulations.
4. Remove the existing roofing if necessary.
5. Make sure that the surface is clean and dry.
6. Install base material, if necessary.
7. For single-ply membrane: Cut membrane to required lengths, place over the surface, and heat-seal. For coating: Spray, roll, or brush on coating. For modified bitumen: Apply by heat or adhesive. For polyurethane foam: Spray on foam and apply top coat. For concrete or clay tiles: Lay out and fasten according to manufacturer's guidelines and local regulations. For metal materials: Contact a professional.
Use a roofing calculator. Because a cool roof can slightly increase heating costs, use one of the roofing calculators provided by the Environmental Protection Agency and the Department of Energy to determine the overall potential energy savings for your home.
Use the recommended insulation with the roof. The amount and the insulating value (R-value) you need depend on geographic area.
Install properly for maximum benefit. Lifespan of the surface and effectiveness of reflectivity depend on proper installation. If you're unsure about installation, hire a professional contractor.