Radiant Barriers

Taking a shine to energy efficiency. Top photo: The SuperAttic treatment from Dr. Energy Saver incorporates a radiant barrier with rigid foam insulation that's installed to the bottom edges of rafters. Bottom photo: Installing sheet-type radiant barrier panels between rafters is a good option when the attic has blown-in insulation.

Many people depend on radiant barriers to prevent car interiors from overheating on sunny days. They install a flexible, shiny heat shield across the car's front windshield. The attic radiant barriers used to improve home energy efficiency work just like an automotive heat shield, reflecting heat away from the living space during summer months, and back toward the living space during the heating season.

When used in houses, radiant barriers go by other names, such as "reflective insulation" and "radiant barrier insulation." But there's a distinction in how both items function. A radiant barrier slows heat transfer by radiation, while insulation slows heat transfer by conduction and (in some cases) convection.

Radiant barriers vary by type, cost and performance

In houses and other buildings, radiant barriers are most frequently installed in the attic space. In this application, the radiant barrier's primary job is to reflect solar heat back toward the outside during hot summer weather.

Radiant barriers come in different forms. Some consist of a plastic sheet with a reflective foil facing. A radiant barrier "bubble wrap" is also available, which provides some extra insulation value in addition to a radiant barrier. In other cases, the reflective surface is put on one or both faces of rigid foam insulation panels, again combining radiant barrier protection with insulation.

A radiant barrier can also be applied to the underside of roof sheathing as a shiny, spray-applied paint. However, paint-on radiant barriers are not nearly as effective at reflecting heat as other types.

Radiant barrier benefits:

• Cut summertime cooling costs by as much as 15%. Savings will be greatest in hot climates.
• On hot summer days, a radiant barrier can lower attic temperatures by as much as 30 degrees F.
• When installed against attic rafters, a radiant barrier will improve the performance of blown-in fiberglass or cellulose attic insulation by keeping attic ventilation air away from the insulation.
• With a radiant barrier, items stored in the attic are less likely to be damaged by high temperatures.
• Ductwork and air handlers installed in the attic perform more efficiently when a radiant barrier is installed above this equipment.
• During the heating season, an attic radiant barrier reflects warmth from the house back toward the living space.

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