The US Department of Energy Solar Decathlon is a biennial competition that challenges college teams to build affordable, energy-efficient and aesthetically pleasing solar-powered houses. Team Austria (Vienna University of Technology) has just been announced the overall winner of 2013 event at Orange County Great Park in California, after the closest competition in its history. Second place went to University of Nevada Las Vegas and DesertSol, with the Czech Technical University achieving third place overall.

This year marks the first time that all of the entries tied for a win in the Energy category, as every house was successful in producing more energy than it consumes.

The Austrian team also shared a joint third-place award for the Engineering category. The team's LISI (Living Inspired by Sustainable Innovation) house is a tribute to the forested regions of Austria, but also showed its relevance to the temperate Solar Decathlon site as a model for open space and outdoor living with generous deck space and a fully opening living area.

With a theme that stresses the importance of wood, the LISI house is built of 93 percent timber, including wood fiber and cellulose insulation, baked ash cladding, silver fir ceiling panels, oiled oak on the patio and ramp, and pressed bark chip on the walls of the bedroom and bath spaces. The team uses the analogy of a tree to explain the timber core as trunk and the lace-like curtain which surrounds the structure, as leaves. The curtain, the house’s most striking feature, is a Teflon fabric that has been cut in a pattern designed by the students but which is very robust despite its delicate appearance, and is similar to material used by the military for camouflage. It provides UV protection for the open areas of the house and light weather-proofing.

Measuring 60.9 sq m (645 sq ft) inside, the house includes patio/deck space at front and back with automated screens and awning for shade. The internal core of the house can be closed off in cooler weather with a series of triple glazed sliding doors. A sub-floor ventilation system maintains a comfortable internal temperature and is part of an overall energy system that includes photovoltaic panels connected to a smart management system, two high-efficiency air-water heat pumps to supply cold and hot water, an ERV heat exchange system and even a system for recovering heat energy from shower run-off.

The design is a cool, modern, elegant house with an extended roof at one side that creates a further enclosed side patio protected by an open timber wall. The bed and bathrooms are snug spaces that take up the minimum of the house’s free floor space, leaving the majority to the open living/dining/kitchen/patio spread.

While it makes for a cool, breezy living experience, the house will be modified with increased insulation for its future exhibition in Austria.

Second place overall went to the team from the University of Nevada, Las Vegas, for their DesertSol house, which was designed to reflect the "spirit" of the Mojave Desert. Materially, this was one of the more interesting houses with its weathered timber cladding and rusted metal patio screening and exposed steel elements. TimberSIL, a fireproof glass-infused wood product was used for the decking surrounding the house and reclaimed snow fence is used on the cladding. Internal details like the clerestory across the front wall and windows at varied heights and sizes, including floor-level openings, made this a more dynamic interior than we are used to seeing in these houses. The little hallway was given a dropped ceiling to emphasize the larger spaces of the kitchen/dining and bedroom at either end.

DesertSol also has the full array of energy technologies, including passive elements such as shading and ventilation and a layered insulation system that brings it to an r30 rating for the walls (against a standard of around r18). The UNLV team were the only US team to place in the top three, and shared a joint third place for the Engineering award.

Another European entry, the AIR house (‘affordable, innovative, recyclable’), created by the team from the Czech Technical University, took the overall third place prize, as well as first place in the Architecture category and second place for Engineering. The most immediately notable feature of the house is the "second skin" a louvered timber screen that lines two sides of the house and "floats" over the roof, providing pergola-like walkways and shading the cladding from direct sunlight. The house was built using CLT (cross-laminated timber) in a structural capacity, a technology that has yet to be embraced in North America, where the resources exist but where prejudice to all-timber buildings is still prevalent. AIR was designed around the idea of creating a home for people aged 50 or more whose children have left home and who have retirement in mind. It follows a typology of Czech country retreats, but offers a model that can be used year-round.

The title also refers to "a breathable house," the team says, and uses all natural materials. AIR house has the standard (for the Solar Decathlon) high-tech energy systems, but these have all been hidden in order to emphasize the more natural experience of the wood.

The indoor-outdoor design of all of the houses was tested in the high Santa Ana winds, common for this time of year, that hit the Great Park this week. And all were said by the organizers to have come through in great shape.

According to the founder of the Solar Decathlon and current director, Richard King, the event has gone beyond any of his initial expectations. He pointed out that the recent Solar Decathlon in China attracted 250,000 visitors. Asked how the competition has changed, apart from the increased sophistication of the technology, he says "the public have become much more knowledgeable, they ask a lot of hard questions about the how and the why." A sign, perhaps, that in the Decathlon’s home country more people might begin to embrace the possibilities of energy-efficient living.

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