Homeowners thinking about adding insulation to their attics to reduce heating and cooling bills may want to consider the less expensive alternative of installing reflective radiant barriers, a state-funded research group in Florida says. But other groups are not so sure.
With the aluminum-foil-like product installed on the ceiling of the attic and 3 1/2 inches of conventional batt insulation on the attic floor, a house will be as energy conserving as a similar home with nine inches of the same insulation and no radiant barrier, the study showed.
Subrato Chandra, a senior researcher with the Florida Solar Energy Center in Cape Canaveral, predicted that similar results would be found in homes along the East Coast as far north as Baltimore -- that is, in humid climates where more energy is consumed in summer cooling than in winter heating. However, Chandra said he would wait for similar reports from other groups in other climates before projecting results elsewhere.
The studies, conducted by Philip W. Fairey III, principal research scientist in the research and development division at the center, convinced Florida officials to recognize the use of radiant barriers as an improvement over attic insulation, or a partial substitute, effective next July 1 in the Florida Model Energy Code.
D.C. building code officials said there is no prohibition against using the barriers in the city, but the Florida center's studies are too new for officials in Maryland and Virginia to have considered authorization of the barriers as a partial substitute for some of the insulation thickness.
To allow other states to consider granting the same recognition to the heat-reflective foil, Fairey has presented his findings to the American Society for Testing and Materials (ASTM), a nonprofit group that offers code authorities throughout the country a consistent basis for comparing the properties of materials. ASTM, which is reviewing Fairey's conclusions, previously had reacted less confidently to the benefits of radiant barriers after its own performance testing showed that the foil must be installed to demanding standards to get the benefit.
Insulation is graded by its resistance to the flow of heat fluid. This is expressed in terms of an "R-value," such as R-11, which corresponds roughly to a 3 1/2-inch insulation batt, or R-30, which is provided by a batt of about nine-inch thickness.
Fairey's tests, run this past summer, show that an attic with R-11 insulation, a radiant barrier vented to the outside air and with both sides finished to a reflective surface can match the energy efficiency of an otherwise identical attic with R-30 insulation and no radiant barrier.
An R-19 attic with a barrier tops an attic with only R-19 insulation by 43 percent, even with the top side of the barrier covered with kraft paper to eliminate reflectivity, according to Fairey.
In the tests, the center found that the best way to install a radiant barrier is to hang it between the attic ceiling's structural members and drape it below the roof decking so that it sags enough to create an air pocket. The foil then would become the attic's visible ceiling. Placing the barrier on the attic floor does not work as well.
Insulation manufacturers have expressed deep concern about the findings that Fairey presented to ASTM's Subcommittee on Reflective Insulation, but the center attributed this to a fear of lost sales.
Insulation installers, however, could benefit if more building codes accept the center's findings. R. Hartley Edes, executive director of the Rockville-based Insulation Contractors Association of America, has had his group explore the effectiveness of barriers as a "good opportunity for the members" to get new business.
However, not many ICAA members use the foil because there is so little hard proof of its effectiveness. Edes said Dave Yarborough of the Oak Ridge National Laboratory in Tennessee, who also has been researching the barrier, has told the association to hold off recommending its use until more testing is done.