GE’s Boston headquarters may grow by a third

General Electric offered its first detailed description of what its new Fort Point headquarters will look like in a letter filed with the Boston Redevelopment Authority Thursday, and it’s bigger than many of us expected.

The industrial giant plans to build a 12-story structure with 293,000 square feet alongside two older brick buildings on Necco Court that will be renovated. This means the three-building campus could be as much as a third larger, in terms of floor space, than what was initially discussed.

An early design of GE’s Boston headquarters the company was considering that was inadvertently posted.

GE spokeswoman Susan Bishop said the increase was driven by an interest among GE’s executive ranks to add more space for startups, events, and community uses.

“Our thinking has evolved [about the size],” Bishop said. “We actually realized there was more of a benefit to GE to having more convener space, and the site could accommodate more, and we said, ‘Let’s bump it up, let’s put more convener space in there.’ ”

GE and city officials had previously said the entire complex — the two older buildings and the new one — would total about 300,000 square feet.

But vice president Ann Klee, in Thursday’s letter to the redevelopment authority, said the new building alone would approach that amount. The letter doesn’t specify the square footage of the two six-story Necco Court buildings, but they currently each have about 55,000 square feet of floor space. GE hasn’t said how much space would be in those buildings after it’s done with renovations. So it’s hard to know exactly how much floor space the three buildings will offer, but it’s likely to be in the range of 400,000 square feet.

In January, GE announced that it would move its headquarters to Boston from Fairfield, Conn., and eventually employ as many as 800 people in the new complex.

“The way to think about the space is it’s not just 800 GE employees in there,” Bishop said. “You have maker space, you have coffee shops, you have community meeting space, you have labs, a ‘digital foundry’ like we just launched in Paris. . . . We are very focused on trying to help use the space to change the culture of GE as we transition to a more tech-focused, digital industrial [company].”

The three-building project would be constructed on a 2.5-acre site GE is buying from Procter & Gamble, a piece of P&G’s Gillette campus. MassDevelopment would eventually own the two older buildings, allowing state funds to be used to improve the site.

The brick buildings would be connected by a shared lobby, with elevators set within an atrium and winter garden, Klee wrote. The new building would be connected to the brick buildings by a pedestrian bridge and a space called GE Plaza, a new pedestrian passageway that would run from Necco Street to Fort Point Channel, partly covered by a transparent canopy. GE also plans to set aside about an acre for open space for the public’s use.

Klee wrote that the project would be consistent with the city’s master plan for that part of Fort Point. The project would include office space, “maker space,” a bistro-cafe, a coffee bar, a museum, lab space, and meeting areas. The ground floors, Klee wrote, would comply with state waterfront regulations that require much of the space to be open to the public.

“The Project will reflect the Project Site’s industrial past and GE’s digital future,” Klee wrote. “GE is committed to maintaining resiliency, sustainability and transparency as thematic pillars for the overall design of the Project.”

Bishop elaborated on the resiliency aspect, saying GE’s design will take into consideration possible flooding of the area if the waters in Fort Point Channel rise.

GE has hired the architectural firm Gensler to design the headquarters.

Executives will start moving to Boston this summer, to temporary space on nearby Farnsworth Street. Company officials hope to open the Fort Point complex in 2018.

To entice GE, state and city officials pledged as much as $120 million in state infrastructure funds and up to $25 million in local property tax breaks over 20 years.

The increase in the size and scope of GE’s headquarters makes it more likely the city’s tax relief will reach that $25 million level.

But John Barros, the city’s economic development chief, said Boston’s net gain in property taxes will also increase, even after the tax breaks are factored in. The specific size of GE’s future tax bill and how the tax breaks will be applied are still being negotiated, and the new information about the headquarters will help with those discussions.

“This letter has clearly begun to give us the kind of detail needed to have that conversation about how we apply those incentives,” Barros said. “GE developing a larger space — providing these other amenities and yet staying within the size that the community wanted — are all good things.”