Construction can be an arduous and unpredictable process, full of hazards and delays—except for the case of a recent residential project in Berkeley, in which an entire four-story building took as little as four days.

Berkeleyside reports that a 22-unit housing complex at 2711 Shattuck went up at a rate of one story per day in July and will soon lease to UC Berkeley to use as student housing.

It turns out that this is the first building created with SF-based prefab developer Patrick Kennedy’s trademark MicroPADs, tiny modular apartments modeled on shipping containers, which Kennedy manufactures in China and ships to building sites.

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In a past interview with Curbed SF, Kennedy testified that the MicroPADs are designed to snap together like Lego bricks as construction crews haul them into place via crane, but this was the first time the technology was tested in a real, soon-to-lease development.

According to Berkeleyside, the homes at 2711 Shattuck are larger than the 160 foot prototype Kennedy displayed at his SoMa offices in 2016, measuring out to about 310 feet—larger than some San Francisco SRO rentals.

A 2016 report by Berkeley’s Design Review Committee notes that the application for 2711 Shattuck dates to 2009; the city initially approved it as a hotel before switching the permits over to residential uses.

In a 2015 letter, John Casner, president of the real estate venture firm Casner Capital, cautioned Kennedy that financing such a small project as a hotel would be difficult, noting that “long-term financing to take out a construction loan is likely to be extremely difficult if not impossible to find.”

Switching the project over to long-term residential use opened up the spigot. According to architects Lowney Arch, 2711 Shattuck is “the first [building] to be built using this technology in the US.”

Kennedy has lobbied San Francisco for years to build new modular housing on disused public property as a response to the homeless crisis. City Hall has balked at the price, which it calculates as less efficient than its current SRO stock.