How do you turn a hulking concrete garage above one of downtown’s busiest streets into a glittering garden of towers without ever closing the garage?
We’re about to find out.
The $1.5 billion re-do of the Government Center Garage into one of the biggest developments in downtown Boston hinges on a pretty nifty trick: turning the garage itself from an unloved albatross into the foundation of the entire project.
“It’s not as if you can just swing a wrecking ball at this thing,” said Tom O’Brien, managing director of the development firm HYM Investment Group, which is turning the huge garage into the base of two new skyscrapers, a third mid-rise apartment building, and a plaza of low-rise buildings along the Rose Kennedy Greenway.
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Instead, HYM will carefully take down parts of the garage, while remaking other sections so it can continue to provide parking during and after construction. In some places whole sections of the garage will be demolished, while elsewhere HYM will slice off portions to make way for several of the buildings; the remainder of the garage will serve as a platform that unifies the complex.
“Every piece of the garage has been mapped out. There’s a plan for exactly when and how we’ll take down or reuse each one,” O’Brien said.
The work has already begun. Inside, behind walls of green construction netting and orange barricades, workers are realigning electrical systems, redesigning traffic flow, and building a new exit ramp out to tiny Bowker Street, to replace the circular ramp along New Chardon Street.
Just reworking the garage will cost $25 million. But that’s far less than what it would cost to build a new garage from scratch, or to put the 1,100 parking spots underground at a price of perhaps $150,000 apiece. And it means the developers can keep collecting $375 a month from hundreds of commuters, even during construction.
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“That cash flow is important to the overall finances of the project,” said O’Brien, as the parking proceeds will allow him to keep rents in the office tower lower.
The portion of the garage over Congress Street to the edge of the Rose Kennedy Greenway will be demolished once HYM starts work on the 43-story office tower.
That will take about 12 months, in part to minimize disruption to the busy street below, which will be opened to sunlight for the first time in decades. It will make room for a new pedestrian plaza ringed by offices, retail, and a hotel between Congress Street and the Greenway.
It will also eliminate about half the garage’s 2,300 parking spaces. What remains — still a full city block nine stories tall — will essentially be wrapped by the lower floors of the office tower and two apartment buildings. The inner core of the garage will become a platform for the towers that will rise up to 500 feet. And the garage roof will host an acre of outdoor space.
So when done, the concrete colossus will still be there, just hidden. And still parking cars.
“As much as it’s not pretty, it still serves a purpose,” O’Brien said. “That’s key to this whole thing.”
Tim Logan can be reached at tim.logan@globe.com. Follow him on Twitter at @bytimlogan.