The Effects of Reflective Attic Insulation On a Roof

Characteristics

• Reflective attic insulation materials are usually made of aluminum, which has excellent reflective properties. The thin aluminum material is usually attached to another material such as plastic film, kraft paper, cardboard or insulation materials. This makes the barrier layer easier to attach to the attic roof or on the attic floor and prevents buckling or creasing once the barrier is installed. Liquid, spray-on coatings are available that can cover the attic floor or ceiling, with the insulation material added afterward.

Effectiveness

• Reflective insulation barriers applied to the attic ceiling are less effective on steeply sloped roofs because the gable ends are generally larger. Since no radiant barrier is applied to those ends, more heat can penetrate the attic. Radiant barriers applied to the floor of the attic, in combination with attic ventilation, radiate more heat in these cases, according to a 2000 study by the University of Kansas. In addition to climate, the barriers' efficiency and money-saving properties depend on the type and color of roofing material, the barrier's emissivity rating, reflectivity and the angle of the roof. Reflectivity and emissivity numbers range from 0 to 1. Look for low emissivity ratings of 0.1 or less and high reflectivity at 0.9 or more.

Roof Temperatures

• As the reflective insulation barrier bounces heat back through the roof to the sky, keeping the attic cooler, the process can raise shingle temperatures by 2 to 10 degrees Fahrenheit. Radiant barrier insulation installed on the floor of an attic with proper ventilation may only raise the temperature of the shingles by 2 degrees Fahrenheit, according to the Oak Ridge National Laboratory's radiant barrier fact sheet. Elevated roof temperatures are unlikely to affect metal, tile or single-ply membrane roofing materials, according to the Florida Solar Energy Center. White roofing materials reflect more heat away from the roof before it penetrates to the reflective insulation barrier and thus receive less reflected heat from the attic space.

Shingle Warranties

• Whether the additional heat transferred back to the roof by the radiant barrier has a detrimental effect on the roof is unknown, according to Oak Ridge National Laboratory. Not all shingle manufacturers issue warranties for their products if the home has radiant barriers in the attic. Check with your contractor and the shingle manufacturer to make sure the roof's warranty will not be invalid if you install reflective attic insulation.

Tip

• If you plan to install radiant barriers or reflective insulation yourself, check on local fire codes and building regulations first, and be sure to read and follow the manufacturer's installation instructions.