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Iowa State University's Interlock House was the plain Jane among the 20 student-designed-and-built houses competing in the 2009 Solar Decathlon: It placed dead last in the Architecture category. But the honey-colored cedar-clad structure wowed judges and visitors alike with its modest but accessible design, and for that it ranked fourth in Market Viability.

The Iowa State team says it had two main goals for its Solar Decathlon entry: Meet all regulations for accessibility under the 1990 Americans with Disabilities Act (ADA), and "interlock" the structure into existing communities, which Clare Cardinal-Pett, an architecture professor and a faculty advisor, says is a much more sustainable approach to building. The group also utilized mainstream, off-the-shelf products so that the net-zero-energy house could be easily replicated.

The concept, aimed at older home buyers, has a number of obvious ADA-compliant features: a no-lip shower, lower-height appliances, wide door entrances, and open spaces. Meanwhile, the student-built cabinetry in the bedroom and in the kitchen is light-colored maple, while the floors are dark-stained bamboo, creating a contrast that architecture student Melissa Vandelac notes helps older people with fading eyesight see more easily into each space, particularly at night.

The heart of the house is an enclosed sun porch with a black stone floor that collects thermal energy during the day and releases it at night, the student builders said. The sun porch features custom-designed movable glass walls from NanaWall that increase ventilation and extend the living space to the outdoors.

The group wanted to use a NanaWall system to divide the interior space, but adding that element would have significantly increased the home's cost and would not meet the school's desire for a home that could be easily replicated, says Brandon Vong, an architecture student. So, the team divided the living room and bedroom with a simple but attractive floor-to-ceiling beige-color curtain.

The house does have one notable technology. The students incorporated an innovative evacuated-tube solar hot water collector that heats the house, supplies hot water, and recharges the desiccant dehumidification system during the summer.

For the rest of the technologies, Iowa State stuck to the basics. The team incorporated two types of photovoltaic panels. The main solar array includes crystalline silicon PV modules with an integrated thin-film layer that the students claim adds about 10 percent more power. A smaller array is made of custom thin-film modules integrated into the southern and eastern window shade louvers and the tracking louver array on the roof.

Another energy-efficient feature is the entry door from Pella, a prominent Iowa manufacturer, which vacuum seals and has an R-value of 45. For a decorative touch, the students covered the wide door and two smaller side doors with panels made from 80 percent recycled grain and etched them with a wheat motif.

In addition, the dwelling is insulated with spray polyurethane foam manufactured from soybean oil.

The off-the-shelf technologies proved successful, because the house placed sixth in Net Metering and fifth in Engineering out of 20 competitors.

There are a couple of other things about the Interlock House that are worth mentioning. For the exterior cladding, the team purchased a plot of land in Wisconsin, harvested the cedar trees, and then replanted the plot.

Furthermore, the Iowa State team collaborated with students in three College of Design classes—a furniture studio, an advanced ceramic studio, and a file-to-fabrication class—to deck out the house with some unique touches. The resulting one-of-a-kind collection includes chairs that can be side tables, bird feeders made of metal and bio-based plastic, and ceramic tiles.

Jean Dimeo is Chief Editor, Online for EcoHome magazine.

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