How would you create a city block that was fully sustainable? A competition to redevelop an entire block of downtown Dallas asked urban planners to do just that, and the finalists have just been announced.

The competition is billed as more than pie-in-the-sky. The Central Dallas Community Development Corporation, a non-profit, is acting as lead developer, and the lot involved is currently a parking lot across from City Hall. In other words, there's quite a long list of issues to be resolved before any design becomes reality. But the three finalists were an impressive lot:

Atelier Data & MOOV, two firms in Portugal, imagined a 854-unit housing development modeled after a hillside. With high-tech additions, of course: The southwest side would be covered in a solar shield which, like venetian blinds, could be adjusted to vary heat loads in summer and winter; the northeast side would be faced in hay bales, for extra insulation:

Little, based in Charlotte, North Carolina, imagined a mixed-use tower that doubles as a vertical farm. The vegetation would feed cattle on the roof, grazing at a "sky pasture"; food would be grown on-site, and power would come from the solar panels:

David Baker and Partners Architects working with Fletcher Studio, each based in San Francisco, proposed the least monolithic and most sociable design of the lot. Their design integrates a multi-modal transit center; a variety of "micro-retail" spaces; and an urban agriculture program.

The competition was held by Re:Vision, part of a series of competitions that has posed challenges ranging from urban transportation to green jobs. The panel of judges included Aidan Hughes, a principal at ARUP, and Nathanial Corum, a staffer at Architecture for Humanity. Cameron Sinclair, the organization's founder, and Peter Head, ARUP's director, also served as advisers.

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Read more about the entries on Re: Vision's Web site or at Bustler.