Just 40% of the work will be completed on the Dean Street development site, including foundation work and the erection and assembling of the finished modular units. The FCS Modular facility will be used to build the modular components; it's scheduled to ramp up to full capacity next spring. “So it is all being built in Brooklyn, just not all at the site,” said Mayor Michael Bloomberg at Tuesday's ceremony.

The modular techniques will save time and money as well as cutting down on construction-site waste, according to FCRC, which estimates a 70% to 90% reduction in waste. “The modular construction that will be used for B2 and subsequent buildings at the Atlantic Yards has the potential to really change the way cities are built,” Bloomberg said Tuesday, adding that modular “makes construction cheaper, faster and less destructive than ever.” The company is projecting a summer 2014 completion for B2, during which time two other modular residential towers will get under way.

The cost factor was a key motivation for FCRC in what Gilmartin called “a two-year-plus immersion” in studying modular techniques. Both Gilmartin and Ratner alluded to, and disputed, charges leveled by opponents of the project, who claimed that the developer would build the Barclays Center arena and then walk away from its promise to develop multifamily at Atlantic Yards.

“Our commitment to housing never wavered,” Gilmartin said Tuesday, but in the aftermath of the 2008 capital markets meltdown, it was necessary to find a lower-cost, more efficient way to deliver on that commitment. The company opted for modular, although it had never been employed on a comparable scale in the US.