Radiant barrier foil is a thin aluminum film that works to reflect heat gain. It is typically fastened to the underside of roofs or in attic spaces, where it prevents the heat absorbed by hot roofs from transferring to the home’s interior. Radiant barrier foil is especially effective in cathedral ceiling applications where there is limited attic space. Properly installed radiant barrier foil blocks up to 95 percent of the heat coming into a home from the roof.
There are several passive methods that can be used to reduce home cooling costs. Awnings, curtains and reflective window film keep the sun from entering the house, reducing direct heat gain. Radiant heat is the transfer of heat from a heated object to a cooler object. Roofs are capable of transferring large amounts of radiant heat into the home. Attic insulation helps to prevent much of the transfer of this heat, but radiant barrier foil prevents the heat from even reaching the insulation.
Radiant barrier foil is made of aluminum foil, because of the material's unique heat-transfer properties. Aluminum foil reflects heat but does not absorb and transfer it. Radiant barrier foil reduces interior temperatures, thereby lowering air-conditioning costs by an average of 10 percent.
This lightweight film can be installed during construction or in existing homes. The foil is stapled or tacked to the underside of the roof panels. To take advantage of its heat-reflecting properties, radiant barrier foil must be installed with the reflective foil side facing the interior of the home. The radiant barrier should face an airspace, because it will act as a heat conductor if it is in contact with the ceiling.
There are several radiant barrier systems. It is available bonded to paper, with the foil on one side and paper on the other, or preinstalled on roof decking. It is also available as a double-sided, reinforced foil. Some insulation manufacturers also offer their product with such foil already attached.
Layered foil systems are two pieces of radiant barrier foil that are bonded in sections to create a baffle space between the top and bottom layers of foil. A “chip” form of the foil — small, loose pieces of the foil — can be blown onto attic insulation. This form of radiant barrier foil, while somewhat effective, reflects less heat than the solid film varieties. The choice of radiant barrier type is dictated by attic and roof conditions.