HOBOKEN, N.J. — On summer evenings, the running path along the riverfront here is clogged with businessmen on smartphones tripping over dog leashes and joggers weaving through a stream of strollers. It had gotten even more congested recently as curious pedestrians congregated around a fenced-off parking lot on Sinatra Drive to guess the purpose of the structure being built inside.

“People have asked us if we’re building a waterfront bar,” said a worker, Steve Scribner. “As if Hoboken needs any more. Someone else thought it was a houseboat, or some kind of giant Porta-Potty.”

But even taking into account Hoboken’s love affair with happy hour, there was an urgency to the building process that seemed incongruous. Someone was always there hammering or sawing — and many of the workers seemed a little young for cocktails.

The compact, shoe-box-shaped mystery building is named Empowerhouse, and it is a superefficient, solar-powered house that will compete in the Solar Decathlon, an event sponsored by the Energy Department that will open on Friday on the National Mall in Washington. It was designed and built by architecture and engineering students from Parsons The New School for Design, the Stevens Institute of Technology and the Milano School of International Affairs, Management and Urban Policy.