The news came as a surprise even to those well-versed in metal roofing.
Late last year the Florida Solar Energy Center released the results of a real-world study of the heat gains in houses with different metal roofing materials. The experiment monitored indoor cooling energy usage for seven side-by-side homes in Ft. Myers, during the summer of 2000. Each home was virtually identical except for roofing material (one had a sealed attic and roof deck insulation).
The study showed that white S-tile produced the lowest attic heat gain.
But the home with the white metal roof posted the lowest overall cooling cost.
Compared to a dark gray shingle roof, the study reported, "a white, galvanized metal roof should save a customer who lives in an average-sized 1,770 square foot home approximately $128 or 23 percent annually in cooling costs." Flat white tile offered a savings of 17 percent. Terra cotta roofing, the most popular roofing material in Florida, netted a modest $15, or 3 percent savings over dark shingle.
The thrust of the study, of course, was that reflective colors have significant bottom-line benefits even on pitched roofs with attics.
"The difference seems to be metal's higher emissivity," says Danny Parker, one of the study's authors. "During the night, the metal radiated heat to the night sky better, and so fell below ambient temperatures." This effect, he says, would be even greater in more arid regions such as the Southwest, where clouds would seldom interfere with the radiant transfer.
Metal's emissivity is usually a source of concern. Unpainted metal has emissivities as low as 20 percent, even when it has reflectivities in the 60-70 percent range. This means that it dissipates less of the heat it does absorb and sends it into the building instead.
Painted metal, on the other hand, has an emissivity of about 80 percent -- not as high as some surfaces, but high enough to make for a respectably cool roof.
Metal has other
strong suits relative to other roofing materials, especially for steep slopes,
including weatherability and resistance to mold and fungus, which can darken
The chief weakness of cool metal, in the eyes of most homeowners, is simply aesthetics: most prefer dark-colored roofs, energy costs be damned.
The new reflective pigments made by Ferro and being put into the Ultra-Cool coatings by BASF offer a new angle on the problem. These paints manage to reflect high percentages of solar radiation outside the visible spectrum, allowing darker colors to remain much cooler.
Classic Products has used the coating, which they call Hi-R, for its aluminum shingles. Since the Metalcon show last fall, several other manufacturers have picked up the product, including Architectural Metal Systems, Custom-Bilt, and Englert.
The BASF coating doesn't achieve the high reflectances of plain white, but it may be the best way yet to cool off residential metal roofs.
Not yet a member? Sign up here
As the #1 educational resource for the residential metal roofing industry, the Metal Roofing Alliance helps match metal roofing contractors with interested home owners in your area. We help consumers decide if a metal roof is right for their home, and when they're ready, provide them with a list of contractors near their home.
After learning about all that metal roofing has to offer through MetalRoofing.com, many homeowners are interested in installing a metal roof themselves. We make this home improvement project possible by directly connecting these homeowners to you, their local distributor.
The goal of the MRA is to promote residential metal roofing by educating consumers on the many benefits of metal roofing. As a member manufacturer, you'll help promote the use of residential metal roofing to interested consumers, and gain access to consumer leads. For more information, contact Bill Hippard, Executive Director, at email@example.com.Member LOGIN