There are flaws in the B2 scheme, say those experienced with modular, especially the "still" construction plan developed by XSite Modular—Forest City's modular-business partner-consultant before Skanska. Unlike an assembly line, still construction is built in place by teams, each assigned to a vertical line of identical units. The approach and the 913 unique modules do not take advantage of the efficiencies of assembly-line production, say modular experts.

O'Hara also maintains that the B2 modules, which include facade panels, are too complete. Most modules don't include the panels because they often cause alignment problems during field fit-up.

FCRC and Skanska declined to comment on the criticism of their approach.

Modular delivery disrupts the economics, workflow, contracts, coordination points, insurance and building regulations of conventional site-built projects. There can be issues with the union building trades. Off-site delivery raises questions even about warranties versus bonding. Is a bathroom pod a product or not?

Plan review also must be completed early, but most buildings departments are not geared up for this.

Transportation, picking, setting, tolerances, on-site stitching and detailing are different from site construction. "I have tremendous respect for logistics, which can make or break a project," says the Stack's Brown. "Transportation is a big piece of the cost."

Global Building Modules—with FXFowle Architects as architect, LERA as structural engineer and Dagher Engineering as mechanical engineer—is trying to market a patented modular system that would solve some of the transportation issues. The concept calls for steel-framed modules that are dimensionally the same as shipping containers; the modules could be produced in port areas of cheap labor and shipped by sea and rail to sites.

So far, there have been no takers. "Everyone is always blown away by how technically resolved the idea is, but each asks, 'Who has done a building?' " says David Wallance, a senior associate at FXFowle.

Project Frog has demonstrated a way around flat-bed-truck limitations for 3D modules. The company supplies kits of parts to the site; only bathroom pods are 3D. "Flat-pack construction is affordable to ship," says Ann Hand, Project Frog's president and CEO.

Modular delivery relies on owner buy-in and early team collaboration. With 3D modular, there is no fast-tracking, but there is resequencing. Design decisions have to be finalized up front, to allow prospective modular builders to price the job and the winner to order supplies.