Assembly Square

Updated November 10, 2026

What's happening

Assembly Square has both the best news in Somerville's commercial real estate and one of its riskier bets. TransMedics Group is taking the entire 188 Assembly Park Drive, a nearly 500,000 sq ft building owned by BioMed Realty, for its global headquarters. It's the largest lab lease in Somerville's history and, by the city's count, takes 25% of the city's vacant lab space in one deal (city announcement, January 13). Now a second tenant has arrived. On October 1 Greystar said Mass General Brigham signed a long-term lease for 100,000 sq ft of lab space on the lower floors of 74M, the 15-story building at 74 Middlesex Avenue. That's more than 20% of the building. MGB will consolidate its pathology labs there and holds rights to expand (Cambridge Somerville Independent, Oct 1).

Meanwhile Divco West, filing as DWCH Assembly Row, LLC, wants Planning Board site plan approval for a 19-story lab building at 120 Middlesex Avenue (ZP26-000038). That's in a market where 1.9 million sq ft of Somerville lab space already sits empty. Divco pitches it as the gateway to a life science corridor that could compete with Kendall Square. When the board heard it on August 6, members worried about adding unusable space to a glutted market. The case hasn't appeared on a posted agenda since, and no decision is in our sources (Planning Board agenda, Aug 6). The Independent thinks the MGB deal could help Divco's case.

You can watch the TransMedics buildout in the permit record:

Building permits: three issued to DPR Construction, with estimated costs of $9.8 million for base-building work on all 12 floors (issued July 22), $13.5 million for Level 10's offices and "command centers" and $25.5 million for Levels 11 and 12 (both issued August 18). That's about $49 million so far, against the company's $175–225 million estimate.
Electrical: between September 3 and 21 the city added permits worth $950,000, $900,000, $895,000, $750,000 and $600,000. They cover power, lighting, fire alarm, data and security on Levels 3, 10, 11 and 12 and the penthouse. Plumbing permits for the upper floors came in the same stretch.
HVAC: on October 5 McCusker Gill applied for ductwork permits estimated at $825,000 for Level 3, $610,000 for Levels 11 and 12, $450,000 for Level 10 and $40,000 for boiler flues. On October 6 J M Electrical filed for HVAC control wiring for "Transmedic Enabling and 3rd Floor" (est. $145,174).

Two other Assembly projects are in the same record:

399 Revolution Drive: after lab fit-out work there in September, Walsh Brothers filed occupancy applications on October 7 for office fit-outs. The work clears out old workstations on the 3rd, 10th and 11th floors and puts in demountable partitions.
300 Canal Street: a September 24 application, still under review, would fit out a 25,729 sq ft one-story tenant space, est. $900,000. The filing doesn't name the tenant.

The UCH-TIF zone covering Assembly Square and East Somerville cleared the Council 10-0 on September 10 and now goes to the state.

Assembly Square is also becoming a river crossing. On September 23 MassDOT approved a $78.7 million contract for a car-free Mystic River bridge to Everett. The bridge is meant to carry fans to the Kraft Group's proposed soccer stadium in Everett. The stadium agreement with Boston and Everett includes $17.5 million for a new entrance on the river side of the Assembly Orange Line station. Mayor Jake Wilson is counting on game-day crowds at Assembly Row for "that meals excise tax revenue" (Boston Globe, Sept 26; Mobility projects).

The story

The TransMedics deal

The city announced the lease on January 13. By the city's account, it brings an estimated $75 million in new tax revenue over ten years and 900 jobs at the site, including 600 new positions by 2032. TransMedics will also put $230,000 a year for ten years into Somerville schools, STEM and robotics programs, and the police and fire departments. The company is moving offices, research and development, equipment manufacturing and a flight operations center into the building. It expects to spend $175–225 million on the buildout and to start operating by January 2028.

The public side: the City Council approved an $18 million tax increment financing agreement, which the city says will bring in four times its value in new revenue. The Massachusetts Life Sciences Center proposed a state package worth up to $18 million more. It's tied to the 600 new jobs, workforce development and equipment. Wilson said the company fits "right in here in Somerville with our growing life science hub." Economic Development Director Rachel Nadkarni used the announcement to market the rest: "Somerville has 1.4 million square feet of lab space ready for occupancy."

For the budget, the deal is real but slow. Chief Assessor Frank Golden told the Council on April 14 that TransMedics revenue phases in over ten years starting in year three. The near-term win is building permit revenue, an estimated $1.8 million (April 14 Council). TransMedics pulled its first building permit by mid-June (June 17 Finance). See The lab glut and the tax base for why one lease carries this much fiscal weight.

MGB and 74M

MGB already owns a large administrative building in Federal Realty's Assembly Row. The 74M lease is different: it's lab space, the kind that sits empty. Greystar's Matt DeNoble said the building "is well positioned to expand its tenant base," and Greystar is marketing the rest of it. The Independent cites local experts who put regional lab supply at about 14 million sq ft. The lease's term and rent aren't public in our sources.

The 19-story lab

The 120 Middlesex Avenue proposal sits in the Assembly Square Mixed-Use District and needs only site plan approval, not a rezoning. It would be new speculative lab space in the middle of the glut. Golden told the Council in April that only five of the city's 10 life science buildings are stabilized. Wilson said converting them to other uses is impractical because they have few windows and specialized air handling. The board made the same argument from the dais in August.

The city as landowner and landlord

In Assembly Square the city has started buying instead of renting. On April 9 the Council voted 11-0 twice, for a purchase and sale agreement and a $7 million bond, to buy the condominium unit that houses the Assembly Square Fire Station. The seller was BioMed Realty, which was liquidating the garage complex. The city had already spent $8–10 million turning the space into a fire station and was paying $363,699 a year in rent. Finance Director Ed Bean put the 28-year cost at $12.4 million to buy versus $13.4 million to keep leasing (April 9 Council). On May 28 the Council expanded the 2010 Assembly Square District Improvement Financing district to cover the station at 45 Middlesex Avenue and the straightening of the Middlesex/Mystic Avenue intersection. That lets the city borrow short-term at about 2.5% instead of 3.5% (May 28 Council).

Two other threads run through the neighborhood. The UCH-TIF housing incentive zone covers parts of Assembly Square and East Somerville along East Broadway, McGrath Highway and Assembly Row; see Housing tax-break zone for East Somerville and Assembly Square. And the city's combined sewer plan puts a 7.4-million-gallon storage tank at Assembly Square, probably on the former Christmas Tree Shop parking lot; see Combined sewer overflows.

What's next

120 Middlesex Avenue: the 19-story lab returns to the Planning Board whenever it's re-posted. The board raised concerns August 6, and no decision is in our sources. See Before the boards.
74M: MGB's pathology consolidation, and whether Greystar leases the other four-fifths of the building.
188 Assembly Park Drive: the October HVAC applications are still pending. Operations start by January 2028, after a $175–225 million buildout.
About 2029: the Mystic River bridge opens if MassDOT's three-year construction estimate holds. There's no date yet for the Assembly station's river-side entrance.
2032: TransMedics' target for 600 new positions, the job count the state incentive package is tied to. The city's tax revenue phases in over ten years starting in year three.
UCH-TIF zone: approved by the Council 10-0 on September 10 and awaiting state review. Each tax deal under it still needs its own Council vote and state sign-off. See Housing tax-break zone for East Somerville and Assembly Square.