Image courtesy of Stantec Architecture and D/R/E/A/M Collaborative

The scope of the massive Dorchester Bay City project is expanding further to nearly 6.5 million square feet with developers’ acquisition of a neighboring parcel containing the Boston Teachers Union headquarters.

Accordia Partners and Ares Management previously were seeking approval for 4 million square feet of commercial space and 1,740 housing units on 34 acres, including the former Bayside Expo Center property and a Santander Bank-leased office park at 2 Morrissey Blvd.

The development team is acquiring 180 Mt. Vernon St., a 2.7-acre parcel next to the Bayside property, with plans for three new buildings adding 390,300 square feet of office-research space, 188 housing units and 17,300 square feet or retail-commercial space, according to a document submitted to Boston Planning & Development Agency.

The addition of the new property improves connections from the original site to Dorchester Shores Reservation, Day Boulevard and Moakley Park, developers said in the filing. 

Specifically, it would enable extension of a central vehicular, bicycle and pedestrian right of way from Day Boulevard to Morrissey Boulevard and all three properties, siphoning traffic away from the notorious congestion at Kosciuszko Circle.

“The future creation of this mobility corridor will complete one of the most fundamental aspects of the Columbia Point Master Plan and allow for an alternative route for all modes of travel to bypass Kosciuszko Circle, energize the Dorchester Bay City site, and allow unfettered access to the Dorchester Shores Reservation and Moakley Park and Carson Beach,” Ares and Accordia stated in the filing.

The original plan under review by the BPDA calls for a six- to 10-year buildout for the development including housing, offices, lab and retail space and new connections to the Boston Harborwalk.

Developers will present an update on the project during a virtual public meeting at 6 p.m. on Wednesday.