Sun-powered, prototype homes exhibited on the Mall a few weeks ago showed how solar energy can be harvested to conserve energy. But they also showed that, with creative architectural design, an extraordinarily compact dwelling can be commodious, well built and beautiful.

Some of the 19 homes on display were decidedly idiosyncratic and futuristic in appearance. But a few foretold the future in another way. They suggested the kinds of sustainable, affordable homes that America’s home-building industry could be producing for small households decades from now.

Conceived and erected by teams of students and faculty mentors representing universities from across the United States and abroad, the small homes were competing in the biennial Solar Decathlon organized by the U.S. Department of Energy. Decathlon rules stipulated that the total interior floor area of a house could not exceed approximately 1,000 square feet, about the size of a typical school classroom or conventional two-bedroom apartment.

Decathlon means 10 contested events. Accordingly, the 2011 Solar Decathlon set forth 10 categories of achievement for which judges awarded points. Thus, it wasn’t enough only to score points for harvesting sunlight and saving energy. Each house was also evaluated for affordability, comfort, engineering efficiency, aesthetic qualities and potential market appeal.

Despite the decathlon’s common rules and goals, the 19 homes varied greatly in form, size, materials, use of technology and climatic response. Purdue University’s traditionally styled, Midwestern bungalow would aesthetically harmonize with suburban subdivision homes anywhere in America. With its familiar, homey appearance, it was a favorite among visitors.

By contrast, the team from the Southern California Institute of Architecture and California Institute of Technology created a geometrically abstract structure covered almost entirely with a thick quilt of insulation encapsulated in white, vinyl-coated fabric. It bore little resemblance to a house.

Generally, the homes were well insulated and employed photovoltaic solar panels on roofs or walls to generate electricity. Green roofs covered some houses. Most sought to maximize the use of daylight to reduce electrical demand. Sophisticated mechanical systems with state-of-the-art controls optimized HVAC efficiency by continually monitoring and adjusting to environmental conditions while recapturing waste heat. A number of homes incorporated landscaped exterior spaces — intimate courtyards or surrounding gardens — serving as both aesthetic enhancements and environmental adjuncts.

Solar thermal energy warmed interior spaces thanks to generously sized windows and glazed doors facing south, east and west. Floors and walls with high thermal inertia absorbed solar radiation and then re-radiated heat into the interior at night. Some homes used the sun’s energy to produce hot water. And a couple of homes captured, stored and released heat by using a chemical phase-change technique: Solar radiation melts and liquifies solid paraffin, which later releases heat as the liquid paraffin solidifies.

Teams aspired to achieve the ideal of complete energy balance, whereby all energy generated by a house equals all energy consumed by the house. Yet with 10 events being evaluated, achieving energy balance might not be enough to carry the day. Indeed, the decathlon’s first-place award for architecture and first-place award overall went to a house that was neither the most energy-efficient nor least costly of the 19 competing houses. Decathlon judges selected the house created by students from the University of Maryland, College Park (where, in the interest of full disclosure, I used to teach).

Named “WaterShed” by the Maryland design team, the wood-framed house didn’t look particularly futuristic, traditional or high-tech. Its rationally composed geometric form, while crisply modern, didn’t appear idiosyncratic or radically experimental. Rather, it felt like a livable, reasonably practical home that people could comfortably inhabit.

WaterShed’s well-proportioned, flexible spaces and ingeniously designed furniture accommodate multiple domestic activities. For example, transforming the bed into a table converts the nighttime bedroom into a daytime office. The daylight-filled living-dining space opens onto a deck and “constructed wetland” in a partially enclosed courtyard. The kitchen abuts a vegetable garden. And the house is beautifully crafted — from cabinetry to construction details — using renewable, currently available materials and state-of-the-art technical systems.

Part of WaterShed’s charm is its openness and sense of expansiveness, despite the decathlon size limitation. Transparency and interplay of interior and exterior spaces make the house seem larger than it is.

Rather than striving only to conserve and balance energy, WaterShed aspires to be an architectural “microscale ecosystem” capturing the energy of rain as well as sun. Paired shed roofs — one vegetated, the other covered by a solar panel array — collect and direct rainwater down to the constructed wetland. The wetland stores and filters both rainwater and gray water from the house, which is then recycled for irrigation and non-potable uses.

The decathlon judges clearly realized that the University of Maryland house was holistically designed. WaterShed exhibited an architecturally compelling balance between energy efficiency, functionality and aesthetic quality. At the risk of being accused of chauvinism, I concur with the judges.

Roger K. Lewis is a practicing architect and a professor emeritus of architecture at the University of Maryland.

“WaterShed” felt like a livable, reasonably practical home that people could comfortably inhabit.