The team is about to build prototype modules. As designed, only 17 of the 930 modules are exactly the same.

Each module's frame is a tubular-steel chassis, which would be delivered assembled to the factory. Chassis range from 20 ft to 45 ft long and are up to 14 ft, 10 in. wide. Floor-to-floor heights are 9 ft, 11 in.

Structurally efficient tubes minimize the depth of the floor-to-ceiling sandwich and are stable in all directions, says Farnsworth. That minimizes distortion of the modules during shipping, eliminating the need for extra strapping.

Each module has both a floor structure and a roof structure. Floors are designed without concrete to minimize weight and keep modules to within available crane capacities. Module corner columns are designed to support the weight of the modules placed above them. To minimize deflection, the long sides of the modules are framed with Vierendeel trusses reinforced with light-gauge-metal strapping.

In the design, MEP risers are located in architecturally inconspicuous places. The main hallway is intended to be finished in the field, so most risers have been located to be accessed from either there or from the back of closets, where access panels are not an architectural issue.

The plan for pipe-connecting pieces is to measure, cut and bundle them up so they can be sent to the site and placed in a closet or hall for installation.

Modules would be wired in the factory, with a single point of connection between modules and a single connection from each apartment back to the main electrical-meter room in the core. Wiring for the home running to the meter room would be coiled up and shipped with the modules. "It is the building equivalent of plug-and-play," says Farnsworth.

XSite has developed a novel factory- floor production plan. Unlike an auto assembly line, there would be teams, called group work cells, each assigned to a vertical line of identical apartments.

"In the factory, crews are essentially building a complete product over and over again on the first floor, rather than 20 or 30 stories in the air," says Amy Marks, XSite's president. That is not only safer than high-rise field construction, it engenders team spirit, says Marks.

On-site, workers would stack finished modules into a full-height steel frame, braced for lateral load resistance. The frame would be erected two to three levels ahead of the modules. Module roofs would be connected horizontally and act as floor diaphragms, distributing lateral loads back to braced frames.

FCRC is so optimistic about its B2-modular scheme that it has had the team complete construction documents.

After residential buildings, the next step may be modular office towers. Sanna says, "Once we crack the office code, there are endless possibilities."