The temperature in your attic can reach 150 degrees on a hot summer day, a situation that if left unchecked can drive up cooling costs by as much as 40 percent. If your attic has less than R-22 insulation—7 inches of fiberglass or rock wool, or 6 inches of cellulose—you should add more. (The U.S. Department of Energy says most homes should have between R-22 and R-49 insulation in the attic. To check what's right for your region, go to the Department of Energy website.
Before insulating, seal around recessed lights, vents, and plumbing and lay down a 6-mil polyethylene vapor barrier. When insulating, place boards across the tops of the joists to walk on, and as you insulate, don't cover or pack insulation around a bare stove pipe, electrical fixtures, or any other equipment that produces heat, unless the fixture is labeled as suitable for direct contact with insulation. Otherwise you risk fire.
Also make sure your attic is ventilated. Gable vents (around $25 each, plus $75 per vent for labor) can lower attic temperatures about 10 degrees; a ridge-and-soffit ventilation system (an extra $200 during reroofing) will reduce attic temperature to around 100 degrees.
When reroofing, use white or pale-gray shingles instead of dark ones. These keep the attic cooler than dark shingles. Cost:
approximately $25 each for gable-end vents; around $200 for ridge-and-soffit ventilation in a new roofBenefit:
Longer shingle life, and up to 20 percent off your cooling bill.