The newest of the 2011 Solar Decathlon’s 10 contest categories – affordability – has become an impressive showcase for design ingenuity, and powerful evidence that building energy-efficient homes doesn’t have to bust the bank.The rules are simple: homes that cost $250,000 or less to build earn the contest category maximum of 100 points, while homes costing more than $250,000 lose points on a sliding scale that tapers to zero at the contest limit of $600,000.On Tuesday, two Decathlon entries – Parsons The New School of Design and Stevens Institute of Technology’s Empowerhouse and Purdue University’s INhome – took first-place honors with scores of 100 points each.The low and high endsThe estimated cost of Empowerhouse, which is designed as low-cost housing for Washington, DC’s Deanwood community, is $229,890. INhome, featuring a traditional Midwestern design, landed at $249,596, while the contest’s second-place finisher, Team Belgium’s E-Cube, took 99.885 points based on an estimated cost of $251,147.In third place, Southern California Institute of Architecture and California Institute of Technology’s CHIP house scored 98.750 points based on an estimated cost of $262,495.The low score for affordability, 46.593 points, went to University of Tennessee’s Living Light, whose estimated cost is $470,574. At 750 sq. ft., Living Light is, paradoxically, one of the smallest entries in the Decathlon, which set the size limit on interior space at 1,000 sq. ft. But the steel-frame building also features unconventional construction, including layered glazing on its north and south exterior walls: an outside single fixed pane of tempered R-1 glass sits on shock-absorbing mounts; on the inside, R-11.4 triple-pane windows, some of which are operable, sit in wood-veneered aluminum frames. Transparent glass dominates the south faÃ§ade while translucent glass dominates the north faÃ§ade, although the operable-window areas on each will be about the same.A juried categoryA Department of Energy press release noted that two jurors spent nine months evaluating each entry to come up with cost estimates and affordability scores: Matt Hansen, founder of Takeoffs Construction Estimating and partner at Licata Hansen Associates Architecture, and architect Ric Licata, a fellow and current western regional director of the American Institute of Architects.“Purdue’s use of a traditional design and construction approach demonstrated high tech energy and control systems for a sophisticated yet conventional market,” Hansen said of INhouse. “The general public would not perceive it as a solar home.” (Click here for a summary of cost estimates.)Architecture and home entertainmentWhile Tennessee may not have been competitive on price, it came in fifth in the architecture contest (another juried category), scoring 92 out of 100 points. The architecture contest winner, University of Maryland’s 920-sq.-ft. WaterShed house, also was, as of 11 a.m. September 29, the overall Decathlon leader. (Click here for a summary of overall standings.)Of the six contests whose results have been announced so far, WaterShed has managed to place among the top five in all but the home entertainment category, which Middlebury College’s Self-Reliance house won with a score of 80.269 out of 100.