How Does LEED Change Windows and Doors?
April 1, 2008
More than 300 homes have been certified under the LEED for Homes program since it launched its pilot program in 2005. Another 8,000 homes are said to be in the pipeline. We asked representatives of two LEED for Homes Providers—organizations that assist builders in meeting these green building requirements and the rating and certification process—about windows and doors used in green homes.
Both Eric Martin of the Florida Solar Energy Center in Cocoa, Fla., and Bill Dakin of the Davis Energy Group, in Davis, Calif., say superior energy efficiency is the number one priority for windows and doors in the projects they’ve been involved with, but both list other concerns as well. “Do not diminish the importance of recycled and reclaimed material properties that are also given credit in the rating system,” says Dakin. The goals of reduced air infiltration and reduced maintenance are also factors.
Martin agrees that the list of issues examined in selecting windows and doors goes beyond energy efficiency. He cites UV rejection, use of windows as part of passive solar daylighting plan, the presence of “green” materials in the window product such as recycled content or certified sustainable wood, and the distance between the place of manufacturing to home site as factors that are considered.
Neither sees the LEED guidelines necessarily changing the number of windows and doors used per home, but builders are looking closely at the performance numbers. “Every LEED Home is different,” Dakin reports. Many custom homes are designed with passive solar features. In these cases, the key is finding windows with low U-factors but higher SHGC to maximize daylighting and solar gains during the winter, while architecture is used to minimize cooling loads. In these cases, Dakin says the builder usually needs to go with a custom window manufacturer, he notes, since many stock windows sold in California are not tuned for this purpose. “In production homes,” he continues, “we are seeing LEED builders specifying high performance windows with low SHGC since optimizing window orientation is difficult to achieve in a production setting.”
“In Florida we look to reduce solar gain basically year round,” Martin reports. This means building orientation, available shade from architectural features and site features, window to floor (or wall) area ratio are all carefully considered in LEED homes.
Both providers also state that, generally, when dealing with window and door manufacturers and/or dealers, LEED designers finding the technical support they need to answer questions and make optimal use of these products. “Being able to locate the NFRC ratings for the windows online is important for the consultants and design team to properly evaluate the building performance,” notes Dakin. “Some manufacturers are better than others.”
When it comes to evaluating the energy efficiency of windows and doors, both put a great deal of emphasis on the NFRC ratings. “For me, it’s the performance numbers,” Martin states. “Whether they represent efficiency beyond Energy Star is really up to the overall efficiency goals of the project.” “An Energy Star labels doesn’t mean much to builders, maybe to homeowners. NFRC performance numbers,” he notes, “have more value to the design team.”
As far as green building needs that are not being adequately addressed by the window and door industry, both suggest potential areas for product development. “It is difficult to find windows with low U-factors and higher solar heat gain coefficients,” states Dakin. “You can get custom tuned windows but at a premium.” Given the additional concerns of his market, Martin suggests, “I see a need for more products that have both superior energy efficiency and impact resistance.”