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Keeping Homes Cool
As temperatures climb during the summer months, homeowners are looking for ways to keep their houses cool without heating up their air conditioning budgets. There are a number of ways homeowners can keep their homes cooler, such as planting shade trees around the home to keep the sun off the roof, or using awnings, overhangs or trellises to provide shading over windows or on the sides of the house. Another strategy gaining attention is using a reflective coating on the roof or exterior of the home.
During the summer months, the hot sun beats down on a home's roof, causing the interior temperature inside to rise dramatically, especially in the attic and upper floors of a home. As a result, the air conditioning system has to work harder and consume more energy to keep the occupants comfortable. Specially designed coatings can reflect away the sun's warming rays, keeping the roof and the home cooler, and helping to reduce energy bills.
Dark asphalt shingles are the least efficient roofing material when it comes to reflecting the sun's heating rays, according to Flex Your Power, California's statewide energy efficiency marketing and outreach campaign. As a result, roofs covered with asphalt shingles tend to heat up quickly, causing the home to heat up as well.
Much like thick paint, a reflective roof coating is designed to apply easily by brush, roller or spray to the surfaces of asphalt shingles, as well as other types of roofing materials, such as wood shingles, cement tiles or metal roofing. The coatings are usually light in color, since light colors reflect the sun's rays better than darker colors, and contain a reflective material such as aluminum flakes or reflective fibers. Roofs covered with these coatings can typically reflect 70 to 80 percent of the sun's heating rays, and reduce a home's cooling load by as much as 10 to 60 percent.
A side benefit is that these coatings absorb only about 5 percent of the sun's rays that falls in the ultraviolet (UV) range, so they also help protect the roof from UV damage. As a result, a reflective roof coating can extend the life of a roof by as much as 15 years.
But not all roof styles or, for that matter, not all locations are appropriate for reflective coatings, nor will these coatings result in the same amount of savings from home to home, or region to region.
Since reflective roof coatings are designed to reflect the sun's ultraviolet rays and minimize the heat absorbed through a home's roof, the larger the relative size of the roof surface, the greater the potential benefit, says Rick Ulrich, founder and CEO of Arizona-based Elastek, which makes Solar Tek Extreme, Solar Mastic and Solar Magic roof coatings. In addition, he notes, "Multiple-story building roofs will experience less dramatic results than a single-story structure," since a single-story home warms up more quickly than a multi-story one, where the solar heating primarily affects the upper floor.
Ulrich says that low-slope roofs - those with a pitch of less than 2 inches in a length of 12 inches - are suitable for coating. (Reflective tiles and metal roofing are among the options for homes with steeper roofs, according to the Environmental Protection Agency.) Be sure to read the manufacturer's recommendations for specific application information and any limitations.
There are formulas designed specifically for various types of roofing materials, such as asphalt, metal or EPDM (ethylene propylene diene monomer) rubber, says Kate Baumann, marketing director at Wisconsin's Mule-Hide Products, which makes elastomeric (rubber-like) acrylic coatings. "Special products are also marketed and should be used for ponded water areas and for skylights and masonry walls," she notes. "When coating metal roofs, a complete system of products is required - cleaner, metal roof primer, flashing grade for metal roof seams, finish coating."
Since the performance can differ from one manufacturer to another, homeowners should check the Rated Products Directory, created by the Cool Roof Rating Council, to find the coating that fits their specifications. Additional information is also available at the Energy Star website (see Cool Home Resources sidebar).
Put It On Thick
Proper application of a reflective roof coating is important, points out Bill Kirn, technical director at the National Coatings Corp. in Camarillo, Calif., which makes a wide variety of roofing and wall coating products. For example, the coating needs to be applied to the recommended film thickness (listed in the product literature). "Typical coating film thickness is 5 to 10 times greater than house paint, so just because the roof is white doesn't mean the product was installed properly."
While asphalt shingles are easy to coat, they must be flat and in good condition, points out Ulrich. However, he adds, "Coating a fairly new roof will kill the manufacturer's warranty on the shingles. The home must have proper venting, and this is often hard for homeowners to determine. Many manufactured homes we see lack full venting and will trap moisture in the roof system if coated, so avoid [coating] them."
In addition, she notes, "On cold but sunny winter days, the heating penalty of an exterior reflective product can be significant. But there is no heating penalty in overcast weather, regardless of how cold it is. If your winters are predominantly overcast and you have extended periods of hot weather in the summer, the benefit in the summer may be worth the penalty on those few sunny days in the winter, for example."
And don't forget about air pollution, which can reduce the reflectivity of white coatings. "Some cities with high levels of particulate air pollution will dirty coatings more extensively," says Ulrich. "Testing has noted drops in reflectivity of 30 to 50 percent [due to air pollution] over a three-year exposure." Reflectivity can be improved by periodic cleaning - even the rain helps, Ulrich notes - and recoating.
A number of companies also manufacture exterior coatings with reflective properties. For example, the Tex-Cote Super-Cote Cool Wall system, from Panama City, Calif.-based Textured Coatings of America, can be applied to exterior stucco and wood walls, as well as decks and walkways. The coating, which is 10 times thicker than ordinary paint, contains special reflective pigments of the same type used by the federal government to keep ships cool.
Tex-Cote coatings are low in volatile organic compounds (VOCs) and have been proven effective in tests conducted by the U.S. Department of Energy. They can lower exterior surface temperatures by as much as 40 degrees F, compared to traditional paints and coatings, according to company information.
The Original Liquid Siding System from Procraft of Virginia is a UV-reflective, water-based permanent exterior coating originally developed as an exterior coating for coastal lighthouses. The Energy Star-rated coating is designed to maintain a significantly lower surface temperature, compared to other coatings and sidings. It can be applied over wood, stucco, brick, block, concrete, masonry and aluminum, although it can't be applied to vinyl siding, and is warranted to last 25 years.
Another exterior reflective coating is the Marathon CWS Coating System, from United Coatings in Washington State. The coating combines 100-percent acrylic elastomers (rubber-like particles) with ceramic microspheres, which join together as the coating cures to form a thermal barrier that reflects the sun's infrared, or radiant, heat, which helps keep the home cooler, according to the company. The two-coat system consists of Marathon Bonding Primer and Marathon Topcoat.
Although there's no doubt about the durability of exterior wall coatings, some remain skeptical about their solar-reflective effectiveness when compared to reflective roof coatings.
"We have not seen any current technology that provides energy efficiency when it comes to siding," says Steve Revnew, director of marketing at Sherwin-Williams in Ohio. "The best way to maximize energy efficiency with siding is to paint it a light color so it does not absorb heat. The darker you go, the more heat will be absorbed, causing an increase in temperature in the home and increasing air conditioner usage."
It's clear that homeowners must do their homework to determine if reflective coatings will help them "keep their cool" when the summer heat hits.
Nancy Christie writes regularly for Smart HomeOwner. She's based in Austintown, Ohio.