From there the unit would move steadily down the line, and, over 21 additional stations, would acquire toilets, indoor walls, outdoor walls, a roof, electric outlets, windows, sinks, countertops and tiling. It takes about a week to finish a unit, Mr. Pace said. The goal is to churn out about 2,000 apartments a year, which would be turned into four- and five-story buildings with 80 to 150 units each.
For workers, factory building seems to mean lower wages but steadier work. Factory OS pays about $30 an hour with medical insurance and two weeks of vacation. That’s about half what workers can make on a construction site, but the work is more regular and, for many, requires less commuting.
Tony Vandewark, a 51-year-old foreman at Factory OS, is OK with the trade-off. Mr. Vandewark lives a few minutes from the factory in Vallejo, where homes cost less than half what they do closer to San Francisco. Contrast that with a job he once had in the Silicon Valley city of Sunnyvale. Mr. Vandewark drove two hours to work and three hours home before deciding to rent a room so he could stay closer to work on weekdays.
“On a job site, you can go do piece work and make really big money, but then the job is gone,” he said.
In addition to not being rained on, one of the key differences between a construction site and Factory OS is that any worker can be trained to do any job. And for old-school trade unions, that is a declaration of war. “The business model is ‘Hooray for me,’” without regard for anyone else, said Larry Mazzola Jr., business manager of UA Local 38, a San Francisco plumbers’ union with about 2,500 members across Northern California.
Factory OS is not anti-union: It has a contract with the Northern California Carpenters Regional Council, which has organized other modular factories and is banking on the technology’s continued growth. The issue is that builders are laid out like a Detroit auto factory, where one union represents all of the workers, and workers can be trained to do any job within the company walls.
That is a huge departure from construction sites, where unions representing plumbers, electricians, carpenters and various other trades each control their piece of the building process. Last year Mr. Mazzola wrote a letter to San Francisco’s mayor, Ed Lee, a month before he died, urging him to deny any city business — such as contracts for subsidized housing — to Factory OS.