Image courtesy of Handel Architects and Studio Enee

A proposed second phase of a lab campus under construction in the South Boston marine park would include another 320,600 square feet of commercial space built on a section of the site previously planned as surface parking.

Developers MP Boston and Beacon Capital Partners received approval for the South Boston Innovation Campus project in 2020, including a 10-story, 380,800-square-foot office-lab-R&D building that broke ground in September 2022. KREF Lending provided $312.5 million in financing in August 2022.

The property, located in the Raymond L. Flynn Marine Park near the intersection of the Northern Avenue and the Massport Haul Road, is owned by the Economic Development Industrial Corp. of Boston. Beacon Capital transferred its ground lease for the second phase to the MP Boston entity in 2020.

The second building would be developed on a southern portion of the 4.4-acre site previously planned for a 70-space parking lot, according to a notice of project change submitted to the Boston Planning & Development Agency.

To preserve the total 325 parking spaces approved in 2020, developers will reduce the parking garage under the first building from 255 to 200 spaces, and 125 parking spaces will be built in a garage beneath the second building. Developers said they will work with Massachusetts Department of Transportation to design and construct a plaza and park located over the Ted Williams Tunnel while maintaining the safety of the tunnel structure.

The 10-story building would include a mix of office, lab and R&D space, to be determined based upon market conditions.

As a public benefit, developers are offering $4.29 per square foot of building area to the city for transportation upgrades for roads and sidewalks in the Northern Avenue corridor.

The project requires a variance from the Zoning Board of Appeals for floor area ratio exceeding 2.0.

The project’s permitting moves ahead despite a pause in leasing activity in the 5.2 million-square-foot Seaport District lab submarket.

The availability rate hit 37 percent in the fourth quarter, according to CBRE, including a 12.6 percent vacancy rate. Landlords for the 20 lab buildings in the Seaport are seeking the highest rents in Boston, however, at $105.80 per square foot on a triple net basis.