Seal the roof and attic
Coat—or replace—the roof. About a third of unwanted heat in your home comes in through the roof, according to the DOE. Apply a heat–reflective roof coating. If you're replacing your roof, the latest Energy Star–certified materials have built–in pigments that block the absorption of heat. (Get a list of manufacturers at energystar.gov.)
Purchase a radiant barrier. Attics can get as hot as 150 degrees in summer. Installing a radiant barrier (a thin sheet of reflective material, sold at hardware stores) in the attic can reduce the amount of heat by 16 to 42 percent.
Insulate your attic. Sealing air leaks and insulating between the attic and house keeps hot air in the attic and is one of the best investments you can make, says Scheckel. (Go to simplyinsulate.org to find out how much insulation you need for your climate.)