Innovative solutions for creating healthy, efficient, eco-friendly homes

Roofs on the Cutting Edge

Flowering succulents may seem more suited to a rock garden in your yard, but at Southface Energy Institute in Atlanta, Ga., a team of workers recently planted rows and rows of sedum, hens-and-chicks and other types of vegetation up on the roof of the nonprofit organization’s new Eco Office. The energy-efficient, environmentally sustainable office building has been designed to demonstrate a number of cutting-edge technologies, such as its new green roof. It’s an example of the latest design trends that can take the environmental benefits of your roof to new heights.

First, the Basics
If you’re not building a new house or addition (or ready to replace your existing roof), you still can implement cost-effective upgrades to your roof to make your house cooler and more comfortable. Most homes have what are called soffit vents underneath the bottom edge of the roof, which allow outside air into the attic. The air rises up and out through vents at the top of the roof through gable or ridge vents.

Your home may have an electric fan in the attic to bring in cooler air, but the truth is it’s a waste of money. “Even though electric fans will reduce the temperature in the attic, they often do so at the expense of [conditioned air you’re paying for in your] house,” says Craig Drumheller, an energy expert with the NAHB Research Center, a subsidiary of the National Association of Home Builders (NAHB), located in Upper Marlboro, Md. “When a fan pulls air out of the attic, the air that replaces it will come from the easiest place possible. If there’s not a good seal between the attic and house, depressurizing the attic [with the fan] can draw air from the living space.”

You’re better off spending your money on more insulation and sealing any gaps or leaks between your attic and the inside of your house, including gaps created by recessed-can lights and attic openings (you can buy a Styrofoam kit at most hardware stores that will fit neatly over your attic stairs). If you’re still concerned that the heat in your attic will turn your holiday candles into red and green puddles of wax, you should consider some new products that can significantly lower the attic temperature.

Keeping It Cool
Heat from the sun travels by conduction through layers of roofing materials to the attic side of the roof, where it then radiates into your attic. A radiant barrier, which is a thin sheet or coating of a highly reflective material (usually aluminum), helps reduce this heat transfer by reflecting the radiant heat rather than absorbing it. Radiant barriers are especially smart for homes in hot climates, where the U.S. Department of Energy reports they lower cooling costs by 5 to 10 percent.

It’s easier to install radiant barriers in new construction, but there are products available for an existing house. “For a radiant barrier to work, it needs to be in close contact with the hot surface, and be separated from the cooler surfaces by an air space at least one-quarter-inch thick,” says Brett Dillon, vice president of Builders Energy Rater in Schertz, Texas.

“On rooflines, [the radiant barrier] should be installed with the shiny side facing the attic, and is best applied along the bottom of the rafters,” Dillon notes. “Rolling the radiant barrier out on the attic floor will work until it gets dusty. Then its performance drops off pretty quickly.” When the radiant barrier is installed on the attic floor, make sure water vapor can pass through it or condensation may form under it during the winter months.

Another cool idea is to use lighter-colored materials on the exterior of the roof. “The benefits of roof coatings are similar to that of radiant barriers,” explains Drumheller. “They function in a similar manner by limiting the amount of radiated energy that reaches the conditioned living space. In Southern climates, the prescriptive attic-insulation requirements are relatively low, and the solar radiation is high, so this is the most appropriate place to use light-colored shingles or other reflective materials,” such as clay tile, metal and white elastomeric coatings. According to a report from the EPA, 10 buildings in California and Florida showed these lighter-colored cool roofs saved 20 to 70 percent in annual cooling-energy use.

“The greenest option, without having to beef up the roof framing, would be to install an Energy Star-qualified metal roof,” says Dillon. A metal roof will have a higher initial price, he notes, but the lifetime cost will be less than having to replace an asphalt shingle roof, which typically is required once or twice during the same period. In addition, a metal roof requires only minimal maintenance, with only a new coat of paint to keep it in top shape for decades, while keeping your attic cooler.

Seal of Approval
While ventilation can be one of the most effective ways to deal with problems caused by humidity in hot climates, it also can cause problems, especially for homeowners who live in coastal areas and in the Southeast. Condensation in attics occurs when humid outdoor air, entering through vents, comes into contact with cold surfaces inside, such as air-conditioning supply ducts. Water condensation, in turn, can fuel a mold outbreak in your attic.

Dillon, who consults with homebuilders from Texas to Tennessee, is a big believer in getting rid of vents in attics and creating cathedralized spaces, as they’re called in the industry. “Cathedralized attics are insulated along the roofline, have no outside air vents and are conditioned with air from the home’s HVAC system,” Dillon explains. “The best thing happening so far in the world of roof insulation is the application of open-cell spray foam insulation to the underside of the roof sheathing, creating a conditioned attic space.”

Adding the attic to your home’s conditioned space does increase the amount of square footage you’ll be heating and cooling, but it can make your house more comfortable and save you money on your power bill.

“The energy efficiency benefits of the sealed attic are that it brings heating and cooling equipment, along with ducts that were previously subjected to the extreme temperatures of the attic, into a conditioned space that allows them to run more efficiently,” says Drumheller. But he warns that the attic needs to be properly air-sealed and appropriately designed for the climate to handle any moisture problems.

My SIPs Are Sealed
Structural insulated panel (SIP) roof systems are another advanced product that eliminates the vented attic. SIPs are thick panels of solid foam insulation sandwiched between two large sheets of engineered wood — most often oriented strand board, or OSB, though one manufacturer is making them with environmentally friendly wheat board. The panels can be used for floors, walls or ceilings, and have incredible structural strength and insulating values when properly installed.

According to the Structural Insulated Panel Association (SIPA), because of the insulating properties of SIPs, “there is no need to provide a vented attic beneath a SIP roof, and doing so would compromise the conditioned space of the building.” In addition, the association notes most manufacturers of roofing materials specify how to attach their products to the SIPs.

Top of the Line
SIP construction is just one of the new technologies showcased at Southface’s demonstration facilities in Atlanta. The demonstration building is also one of the first in the country to feature integrated photovoltaic (PV) solar panels. Instead of installing large (and what some people consider to be unattractive) solar panels on top of a conventional roof, the Eco Office features an installation of Uni-Solar shingles with the PV cells built right in. The solar shingles blend in well with regular roof shingles.
“The concept is a great idea — getting double duty out of your roofing material — but the price tag is still so high,” says Mike Barcik, a senior research engineer at Southface. “I just don’t think the technology has matured to make it economically feasible.”

That may soon change, thanks to a partnership between SRS Energy, which manufactures the shingles, and CertainTeed Corporation, one of America’s largest roofing manufacturers. “Our first [integrated solar] product will be a synthetic ceramic-shaped roofing tile,” says Marty Low, CEO of SRS Energy. “Its form will be based on a popular tile sold in Europe. SRS Energy will sell both the active tiles with embedded Uni-Solar cells and dummy [non-solar] tiles that are installed alongside to inconspicuously embed solar technology into the roof.” The product will go through market testing early next year and be available for sale in a few cities in late 2009, Low notes.

“The cost to the homeowner for an SRS Energy roof will be comparable to a glazed ceramic roof,” says Low, “but it will include enough solar to power, on average, half of the home’s electrical needs. In solar-speak, the electrical portion of the roof will cost approximately $8 per watt installed, which is currently the average [cost] for typical rectangle solar arrays.”

A Growing Market
Although not as high-tech as solar tiles, vegetative roofs may literally be the greenest roof you can install. More commonly found on commercial buildings, they’re starting to catch on for private homes as well, says Linda Velazquez, who publishes “Residential green roofs started to really gain inroads a few years ago, particularly in the Pacific Northwest and Chicago areas,” she notes. “I would estimate about 450 to 500 residential green roofs in the U.S. overall.”

Green roofs can be installed on existing homes, although it tends to be easier and more cost-effective on new construction. These roofs generally fall into two types: intensive and extensive. Intensive green roofs can be full-scale gardens with trees and shrubs that require intense maintenance, deeper soil layers and flat roofs. Extensive roofs usually include only herbs, grasses, mosses and drought-tolerant succulents that need little care and beds that are only a few inches deep. “A flat roof is not always a prerequisite,” says Velazquez. “If it’s a thin, vegetated cover, it can actually be highly sloped.”

Green roofs can help reduce the urban heat island effect, which results in raised temperatures in densely built areas. In addition, green roofs will last much longer than some conventional roofs, because they’re protected from ultraviolet radiation and extreme fluctuations in temperature. Another advantage is the way they manage stormwater. Green roof systems have been shown to retain 60 to 100 percent of the rainwater that hits them.

The biggest disadvantage is cost. Velazquez says she has seen cost estimates as low as $9 a square foot, but notes that it’s more realistic to see costs of $18 to $20 a square foot.

It’s hard to say which trends in eco-friendly roofing design will shift from pie-in-the-sky to down-to-earth options that are available to us all. The good news is our roofing experts say the dominant trend is improving technologies that will become more cost-competitive, so we can make smart decisions for ourselves and for the environment.