One of the simplest and least expensive ways to lower your energy costs and cool your house in summer is to install a radiant barrier in your attic. Radiant barriers are made of a thin sheet of aluminum or other reflective material laid over attic insulation or secured to the roof rafters. The material reflects the heat absorbed by a roof on hot, sunny days, keeping the attic air cooler and thereby reducing the amount of heat transferred to the living spaces below.

Depending on your climate and the amount and type of insulation in your home, a radiant barrier can significantly reduce your need for air conditioning, which in turn will reduce your utility bills as well as your A/C maintenance needs. Radiant barriers are especially effective if you take other steps to increase the energy efficiency of your home, such as sealing leaks in walls, weatherizing doors and windows, and adding insulation.

In new homes, installing a radiant barrier is easy because it can be applied to the roof decking before the decking is installed, or the decking can be purchased with a reflective material already applied to it. In an existing attic, you can either staple rolls of radiant barrier to the rafters or lay them out on top of the insulation. Attaching a radiant barrier to the rafters is the most effective method to employ, but both methods have their advantages and disadvantages.

Laying the radiant barrier over the insulation is the easiest way to install it, but it’s more likely to get dusty that way, and the Department of Energy estimates that as a radiant barrier accumulates dust, its efficiency can be decreased by up to 50%. It also makes navigating the attic space more dangerous, as you won’t be able to easily identify where the roof joists are located. In addition, water vapor can condense on the underside and dampen the insulation, reducing its effectiveness and encouraging mold growth. If you decide to go with an attic floor installation, make sure to purchase a radiant barrier that allows moisture to evaporate.

Attaching the radiant barrier to the underside of the roof allows for better ventilation in the attic—reducing heat buildup in the summer and removing damaging moisture in the winter—and it does not obscure the locations of joists. However, it can reduce the life of asphalt shingles on your roof. Since the heat is reflected out, shingles can become up to 10 degrees F. hotter than they normally would.

With either installation, make sure the reflective material faces upward so it directs heat away from the house. For your own comfort and safety, try to avoid installing it in the middle of the summer, when your attic is at its hottest. Also, having a helper will make a relatively simple job even easier. Take care not to cover vents or lighting, and be careful not to snag any electrical wiring.

Wear protective clothing, a dust mask, and protective gear on your head as nails sometimes poke through the roof decking. If your attic is unfinished, use a piece of plywood laid on the roof joists to distribute your weight and help you navigate; otherwise, a wrong step could send you plunging through the ceiling below.

The cost of installing a radiant barrier depends on the type of insulation you have, the type of radiant barrier you choose, and whether you hire a contractor to do it or do it yourself. You need more time for a roof rafter installation since it’s harder than just laying radiant barrier over the insulation; plus, you need more materials as the area of a pitched roof is greater than that of the floor. When purchasing the barrier itself, make sure it’s rated Class A by the National Fire Protection Association to meet all building code regulations.