Radiant Barrier Coatings
With miles and miles of unpainted attics throughout the country, radiant barrier coatings can be a hot commodity for painting contractors seeking ways to expand their business.
by Stacey Enesey Klemenc
, most people’s attics are unbearably hot. It’s estimated that about a third of the unwanted heat that builds up in a home enters through the roof. Conventional thermal insulation can slow down radiant heat transfer, but it will not stop it.
The sun beats down on the rooftop, which absorbs the solar energy and heats the roof sheathing, causing the underside of the sheathing and roof to radiate heat downward toward the attic floor. The hot attic also conducts heat to the rest of the house below, making the air conditioner work harder and the electric bill climb higher.
Today’s increasingly energy-conscious consumer may be interested in learning that a coat of good paint — a radiant barrier coating, to be exact — would help alleviate much of this problem.
Radiant barriers, which were first introduced back in the 1930s, are materials that are installed in buildings to reduce summer heat gain and winter heat loss, thereby decreasing energy usage overall.
Many are made of a thin sheet of highly reflective material, usually aluminum, which is applied to one or both sides of a substrate material such as kraft paper, plastic film, cardboard or plywood sheathing. These products are designed to be stapled, taped or nailed to the underside of a roof or the top side of a truss under the sheathing. Some can be applied only during new construction.
Radiant barrier coatings, on the other hand, contain microscopic metal particles that reflect radiant energy. They can be easily applied to the undersides of roofs in existing homes and businesses, as well as new construction. Most manufacturers suggest using an airless sprayer, although many of the coatings can be rolled or brushed on as well.
The physics behind these products, some of which are also referred to as interior radiation control coatings, is similar to low-e glass in windows, with the “e” standing for emissivity.
To properly apply radiant barrier paint, says Lynn Walters, a regional sales manager for Radiance, a low-e line of coatings manufactured by Degussa Building Systems (formerly ChemRex), “Spray the roof deck, rafters, the ridge and any gable ends. You want to encapsulate the entire heat-transferring surface with a low-emissive barrier.”
Foil, on the other hand, can only be applied to the roof deck, leaving gaps that aren’t protected. These rolled goods are not only time consuming and expensive but “everywhere you staple or nail becomes a conductive surface,” Walters points out.
With radiant barrier coatings, he adds, “We can get in and out in a couple of hours.” Plus, his company’s e-0.25 Attic Barrier doesn’t trap moisture like foils are prone to do, he says. “It’s a breathable film.”
Surface preparation is the same as with any other paint application, says Steve Revnew, director of architectural marketing for The Sherwin-Williams Co., which manufactures a product called E-Barrier. “Make sure the substrate is clean, dry and dull to maximize performance.” His company’s low-e coating, he adds, is designed to be used on interior roof surfaces of wood or previously coated metal.
Priming isn’t usually necessary for radiant barrier coatings, and one thin coat will usually do the trick. If you apply an overcoat, the coating will lose its effectiveness.
To be effective and to perform properly, all radiant barriers must face an open air space on one side.
All of these low-emissivity coatings for attics are silver in color. Tinting them will make them lose their radiant barrier characteristics.