Radiant Barrier Coatings

On a sunny summer day, 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 vs. radiant barrier coatings
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.

The upside of coatings
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.

Radiant Barrier Coatings

Taking a closer look
When shopping for a radiant barrier coating, the key number to look for is the emissivity number, says Bob Aresty, president of Solar Energy Corp. (SOLEC) in Ewing, N.J., a company that produces LO/MIT radiant barrier paints. “The closer that number is to zero, the better.”

Emissivity is the ability of a surface to radiate heat in the form of infrared radiation. “A normal roof deck of a home is made of plywood, which has an emissivity rating of .90 or higher. When you spray our product on the bottom of the plywood, the emissivity drops from .93 to .23. When you change the emissivity of the surface, it lessens its ability to radiate heat into the attic cavity.”

When you’re shopping for low-e products and comparing one to the other, Aresty cautions, make sure the products’ claims are backed by third-party testing.

In the real world, he continues, the energy savings associated with low-e paints are hard to pin down because there are so many variables to consider, such as the color of the roof, the presence of trees, how well the home is insulated and so on. “Every building is different,” he says. “But what we see in attic temperature-drops ranges from 10 to 25 degrees F. We’ve had some people report a drop as high as 40 degrees.”

In some areas of the country, homeowners are rewarded for using these products, he says. As part of a city conservation program in Austin, Texas, for instance, users receive a rebate of 7 cents for every square foot of roof. And the state of Florida has a separate section in its energy code devoted to interior radiation coatings.

Where they work best
According to Walters, radiant barriers don’t have a significant effect on air temperatures in well-ventilated attics. He says they are most effective in:

• Locations where there are extreme temperatures in summer;
• Homes with strong western exposure;
• Homes that rely heavily on air conditioning for occupant comfort;
• Older homes with inadequate insulation; and
• Homes with dark roofing materials.

“The coating will last as long as the substrate is kept in good, clean condition,” says Revnew. “If any areas are damaged, the coating should be reapplied to maximize the efficiency.”

Aresty notes one of SOLEC’s LO/MIT paints was recently tested to see how it held up after 13 years. “The emissivity values were still the same as the day it was installed,” he says.

Drumming up business
“Just look at the miles of unpainted undersides of roofs that could benefit from this application. It’s all new business. If you’re quoting an interior or exterior job, throw an extra quote into the bid concerning the attic,” Walters recommends, adding that Degussa can provide you with a formula to figure out an accurate price.

Aresty agrees, adding that his company has a presentation on tape and CD to help with marketing. “You’ve already got your foot in the door. This would simply be an add-on service. It will add value to the house. And in a normal application, this product will pay for itself in five years.”

The coatings don’t support mold growth, they aren’t conductive like foil products and they don’t interfere with satellite dishes or cell phone reception. Plus, a professional painter will already have the airless sprayer necessary to apply the product, so no special investment dollars are needed.

These products offer tremendous advantages to homeowners and a good deal of potential profit to painters, Aresty says. “Painters are missing a terrific opportunity here.”