Re: The Boston Arch (Aquarium parking garage)
The land parcel is about 57,500 sq ft. Assuming half of that becomes open space, that allows a floor plate of 29,000 gsf. 900,000 / 29,000 = 31 floors.
The only PNF ever filed, for the 'Arch' proposal, was for 1.5 million gsf, and a garage for 1,400 spaces, 75 fewer spaces than existing.
At 18,000 gsf per floor, and 12 feet vertical between floors, and assuming no podium base with a larger footprint, you could get 50 floors and 600 feet. (Because of the garage, an 18,000 gsf base is probably ridiculous, so there might be three floors of 29,000 gsf, which would cut the number of tower floors by two or three.)
Whether the numbers work for Chiofaro at 900,000 gsf, its hard to say. He has said he can't afford to build less than 1.3 million gsf or so, because of how much he paid for the garage, and the cost of building a new underground garage.
Another option might be to retain the garage, which has 420,000 gsf, and build a 500,000 gsf building on top of that. If he retained the existing garage, I think that is grandfathered from Chapter 91, and the open space requirement wouldn't apply. But I am also not a Boston lawyer. If he retains the garage, and builds a building with 35,000 gsf area per floor, he gets about 15 floors above the garage.
The article doesn't mention the FAA limit, and don't know whether the Greenway development plan will reference it either.