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Capping energy costs

Brighter, better roof assemblies enhance image and performance

February 01, 2001 |

With building owners measuring energy savings in fractions of kilowatt-hours, the last thing they want is to see those savings going, quite literally, through the roof. While a properly installed roof insulation system is the first line of defense in fighting the energy conservation battle (see "R-Value: Material differences," page 58), other design and material options should be considered. The innovations are driven as much by technology as by stricter energy-use guidelines in the public sector.

For instance, when designing a new state-of-the-art information center for Sonoma State University, Rohnert Park, Calif., San Francisco architecture firm ED2 International supported the college's desire to save energy dollars and protect high-tech library equipment. Known as the Jean and Charles Schulz Information Center, the library features an automated retrieval system capable of storing and accessing up to 450,000 volumes.

Part of the drive for energy savings came from previous experience with roofing at other facilities. The California State University System maintains 23 campuses throughout the state, says Danny Young, ED2's project manager. "With that many buildings, energy costs add up in a hurry," he notes. "So, of course, a main concern was saving as much in heating and cooling costs as possible." ED2 and college officials specified a built-up bituminous roof (BUR) using 130,000 square feet of tapered insulation.

Aluminum sheen

"We topped off the whole roofing system with a special emulsion coating consisting of aluminum and chopped fiberglass, which gave the entire roof a look of aluminum coating," says Young, "and a higher degree of solar reflectivity, which helps with cooling costs."

Indeed, issues of reflectivity and emissivity are quickly becoming as important as the R-value of roof insulation. Dark roofs absorb heat, raising indoor temperatures during cooling season and taxing the air-conditioning load-contributing to higher air-pollution levels as power plants work overtime to meet the demand.

The use of light-colored roofing to help regulate building temperature is nothing new, although it has been largely ignored because of reliance on mechanical air conditioning and relatively cheap energy sources. Recently, however, there has been a resurgence among building teams of looking at alternatives to traditional BUR with black-faced cap sheets, and considering such materials as reflective coatings, white single-ply membranes and galvanized steel.

"I think the reflectivity issue is relatively intuitive, in that everybody knows brighter roofs reflect better," says Michael Werner, commercial market manager for the American Iron and Steel Institute, Washington, D.C. "But still, the complete building design may take literally hundreds of factors into consideration in an effort to reduce energy, and the color of the roof may never figure into that whole equation."

Scientific support

Werner says a study being conducted at the Building Technology Center at Oak Ridge National Laboratory (ORNL) is quantifying the infrared emissivity and solar reflectivity of various roofing materials, which can help infer such factors as energy efficiency and service life. Over three years, researchers are measuring roof temperature, heat transmission, reflectivity and emissivity on side-by-side assemblies. In early results, galvanized steel and white polyester have the most reflectivity, while built-up roofing and asphalt shingles show the least.

Elsewhere, the U.S. Department of Energy has joined Lawrence Berkeley Laboratories and the National Aeronautics and Space Administration (NASA) in founding the "Cool Communities Partnership," which encourages building teams and designers to consider roof temperatures when specifying materials and color. The program mainly consists of remote infrared scanning of ground-level temperatures in key test cities by NASA. An aerial scan of Salt Lake City, for example, revealed that a new courthouse roof of black EPDM membrane roof absorbs so much light that rooftop temperatures soar to 170 F in the summer-while heat emissions from an adjacent light-colored roof barely registered on the satellite's sensors.

The ORNL studies also show that darker roofs degrade faster when exposed to ultraviolet radiation. This fact, coupled with energy and environmental concerns, has building planners looking at roofing materials in new ways.

Sustainable standard

"There's a new, increasingly important standard in roofing, and it's best described in one word: sustainability," says Daniel Varvais, a specialist in cool roofing systems with National Coatings Corp., Camarillo, Calif. "A sustainable roof is one that's going to be in place for a long time, [is] recyclable, won't end up in a landfill, and reduces energy costs."

A similar standard guides facility planning and design at Oberlin College near Cleveland, and is embodied in the recent construction of the A.J. Lewis Center for Environmental Studies.

"The goal is for the building to be a net energy exporter-to create more energy than it uses yearly," says Kevin Burke, project manager of architect William McDonough + Partners, Charlottesville, Va., a specialist in sustainable design. "We conducted several extensive energy models to ensure an efficient thermal envelope." The building team specified a rigid polystyrene foam insulation for wall, floor and roof assemblies, Burke says, because it is reusable and durable and therefore a good fit for the college's overall sustainable design philosophy.

At the extreme end of environmentally informed roof design, however, is the "green roof." Popular in European countries for years, the reputation of the planted roof is only taking root in the United States. Last summer, for example, the Earth Conservation Corps, Washington, D.C., which employs disadvantaged youth for environmental restoration projects, installed donated roofing membrane for a green-roof application at its renovated center.

Katrin Scholz-Barth, director of sustainable design with HOK Planning Group, specified the sod-roof assembly. "I selected the [white PVC] membrane for this project because of my experience with green-roof technology in Germany," she says. "I felt very confident this membrane would work well in this application."

For this project, the green-roof application involved a thin layer of soil and vegetation placed over protection board applied to a waterproof membrane covering the entire roof surface. The technique reduces stormwater runoff, reduces ultraviolet exposure of the building and adds insulation value to moderate temperature extremes and improve energy performance.

While green roofs can increase structural loading and some maintenance costs, they offer net benefits for long-term owners. For that reason-and due to awareness of roof reflectivity and sustainability, says Scholz-Barth-green roofs are finally getting their due. "When I first came here 10 years ago and tried to talk to people about green roofs, all I got were strange looks," she says. "Now, people are open to it."

Mainstream, and green

Perhaps additional high-profile projects will open even more minds. In September, the City of Chicago began planting a 38,000-sq.-ft. green roof atop City Hall. When completed, the demonstration project will yield over 20,000 plants-and copious research on the roof's air-quality, water-quality and biodiversity benefits. That's good news for Chicagoans-and for Scholz-Barth, who might find fewer "strange looks" when she mentions green roofs.

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