Mayor Martin J. Walsh’s efforts to get a skyscraper built on a city-owned property in the Financial District have been complicated by the amount of shadow the 750-foot building would cast on Boston Common and the Public Garden.
So the mayor is proposing a trade-off: Allow the tower to be built on Winthrop Square, but limit future development around the downtown’s few open spaces.
On Monday, Walsh is expected to file legislation with the Boston City Council that would change quarter-century-old laws governing how much shadow new buildings can cast on the two parks. It would effectively exempt the Winthrop Square proposal by Millennium Partners, but bar future projects from casting shadows on the Common and Public Garden.
The measure would also toughen city rules governing shadows from new construction on Copley Square and require a new zoning plan for development in Downtown Crossing and the Financial District.
Money is a big motivating factor for the Walsh administration. The city is due to receive $153 million from the sale of the Winthrop Square property to Millennium and has already pledged to spend the proceeds on Boston Common, Franklin Park, and other parks, and on renovations to public housing in East Boston and South Boston.
The economic benefit from the Millennium building “has been a really big piece of this conversation,” said the director of the Boston Planning & Development Agency, Brian Golden. “We’re focusing on fundamental benefits that flow to all the people of Boston.”
Walsh’s bid to change shadow rules also needs approval from the Legislature and Governor Charlie Baker.
While Winthrop Square is several blocks from the edge of the Common, models developed by Millennium Partners show the proposed tower casting shadows on the two parks for as long as 90 minutes in the morning at certain times of the year, reaching as far as the edge of the Commonwealth Avenue Mall, around three-quarters of a mile away.
The legislation was based on weeks of negotiations the Walsh administration held with people who have raised concerns about shadows from the Winthrop Square project, including downtown residents, park advocates, and city and state lawmakers whose support is crucial to the bill’s fate.
City officials circulated final drafts of the bill Friday afternoon. Several key lawmakers did not return calls seeking comment. Other groups involved in the talks were noncommittal.
“We look forward to reviewing the legislation,” said Elizabeth Vizza, executive director of Friends of the Public Garden, which has objected to the amount of shadow the Millennium building would add to the Common and Garden. “We are continuing to work with Mayor Walsh and the BPDA to ensure that a final resolution provides broad, permanent protections for the city’s landmark parks and minimizes the impact of shadows.”
The project lead for Millennium, Joe Larkin, said he was “hopeful that the City Council will understand the incredible opportunity this development offers.”
The bill being filed Monday includes a new wrinkle: It would make it harder to build a tall building in the Back Bay that casts much new shadow on Copley Square. The administration said as much in new zoning approved last year, but this would write those limits into state law, meaning they could not be undone through zoning variances, which the city often grants to developers.
That is probably intended to win over Representative Byron Rushing, the South End Democrat who helped write the original shadow limits for the Common and Public Garden and has long advocated extending them to Copley Square. Rushing did not respond to messages on Friday afternoon.
Three large projects in the works along Stuart Street — including Boston Properties’ plan for new towers atop the MBTA’s Back Bay Station — already comply with the city’s new shadow rules, said Meg Mainzer-Cohen, executive director of the Back Bay Association. She said other property owners are undecided about the new limits for Copley, understanding that the city benefits by allowing the Millennium project to move forward.
“There has been a lot of discussion going on about this,” she said. “$153 million is extremely important for the city of Boston. We really, truly understand that.”
Another potential hurdle: Representative Aaron Michlewitz’s recent demand that some money from the sale in Winthrop Square be used to help fund the Rose Fitzgerald Kennedy Greenway, which faces state budget cuts. Michlewitz did not return messages Friday, but Golden said Walsh takes his request “very seriously.”Tim Logan can be reached at email@example.com. Follow him on Twitter @bytimlogan.