Historic Boston churches fear towers may cast them in darkness

As city officials debate new rules for shadows impinging on Boston Common, a similar battle is brewing a few blocks away.

Two of Boston’s most historic churches are worried about the effect of shadows that would be cast by a pair of towers planned for atop Back Bay Station. They’re asking city and state officials to reconsider the project and have the support of the state office charged with protecting historic buildings.

Trinity Church and Old South Church are among the organizations protesting plans by developer Boston Properties for the two buildings — 365 and 298 feet tall — along Stuart Street at Back Bay Station. They’ve sent letters to the Boston Planning & Development Agency urging changes to the plan.

The towers are part of a larger overhaul of the commuter rail hub, which the developer says will bring much-needed housing and office space to the area and better link the Back Bay and South End. But much like the 750-foot tower Millennium Partners wants to build downtown on Winthrop Square — which has riled parks advocates worried about new shade on Boston Common — they illustrate the city’s balancing act between height and history.

It’s the sort of debate that keeps recurring as big developments in some of Boston’s most desirable neighborhoods collide with the human scale and heritage that help make them so desirable, said Greg Galer, executive director of the Boston Preservation Alliance. And while some impacts are easy to avoid — no one’s talking about demolishing historic churches, for instance — ephemeral impacts such as shadows are harder to plan for.

The stained glass windows at Old South Church could be darkened if a proposed tower is built at Back Bay Station.Pat Greenhouse/Globe Staff

“People tend to look at concerns about shadows in a relatively narrow and limited way,” Galer said. “But there are impacts that too often get ignored or minimized.”

At Old South, the impact could be felt most acutely indoors, especially on two huge sets of stained-glass windows on the east- and south-facing walls of the church’s sanctuary. One set, directly above the church’s carved wooden chancel and framed by the pipes of its massive organ, is five panels of glass depicting angels revealing themselves to shepherds at the birth of Jesus.

According to shadow studies produced by Boston Properties, the towers would block sunlight from hitting the windows on mornings in December, the Christmas season, during 9 a.m. and 11 a.m. services.

“That struck us as somewhat ironic,” said the Rev. John Edgerton, an associate minister, as he pointed out the north star amidst the elaborate panels. “These windows are beautiful.”

Across Copley Square, at Trinity Church, there also would be new shade on the stained-glass windows. But perhaps a bigger concern is what that winter shadow might mean for the structural integrity of the 140-year-old stone church. Less sun means more moisture, which in winter can freeze and then thaw and generate moss and lichen, said Jean Carroon, an architect at Goody Clancy, overseeing an $11 million renovation of the church that is focused on its west façade, which would be in a shadow under the Back Bay Station plan.

“The building already suffers because of the John Hancock Tower [next door],” Carroon said. “This will definitely increase the impacts.”

Those concerns prompted the Massachusetts Historic Commission to weigh in, sending a letter last week to state environmental officials, who also are studying the project. In it, the commission warned of an “adverse effect” on both historic churches, as well as the Boston Public Library’s McKim Building on Dartmouth Street, the YWCA at Stuart and Clarendon streets, and historic districts in both the Back Bay and the South End.

“The proposed towers will create new shadows on many historic resources in the area,” wrote executive director Brona Simon, who urged Boston Properties to consider alternative plans, including shorter buildings.

The developer declined multiple interview requests. In a statement, Boston Properties executive vice president Bryan Koop touted the public benefits the project would bring and pointed to new zoning in the area that allows its proposed height and limits new shadow on Copley Square itself to two hours a day.

“The project generates even less shadow than is allowable under the restrictions of the recently enacted Stuart Street Zoning, which was the product of a multi-year community planning process,” he said.

That zoning was designed to encourage development along Boston’s so-called High Spine, the corridor between the Back Bay and the South End where some of Boston’s tallest buildings are sited, said Meg Mainzer-Cohen, executive director of the Back Bay Association. Mainzer-Cohen said she understands the concerns about the churches, but she believes Boston also needs to make room for tall buildings if it’s going to grow. Sometimes, she said, that will require trade-offs.

“The city must consider these impacts versus the fact that there’s demand for more housing, more office space, an improved MBTA station,” she said. “These things need to be weighed and balanced.”

Carroon views it through a different lens. The current hot real estate market is a temporary concern, compared with a church she hopes will stand for 1,000 years. Trinity and its neighbors around Copley Square are part of the city’s heritage, and they need to be cared for appropriately, Carroon said.

“These are some of the great buildings of the world, and putting additional shadows on them in winter is not good for them,” she said.

“It comes down to what a community values.”

The Old South Church in Back Bay is one of Boston’s most historic. Pat Greenhouse/Globe Staff