Assembly Square

Updated September 21, 2026

What's happening

Assembly Square holds the single best piece of news in Somerville's commercial real estate story and one of its riskier bets. TransMedics Group is taking the entire nearly 500,000 sq ft building at 188 Assembly Park Drive, owned by BioMed Realty, for its global headquarters — the largest lab lease in Somerville's history and, by the city's count, 25% of the city's vacant lab space in one deal (city announcement, January 13). Meanwhile DWCH Assembly Row, LLC is asking the Planning Board for site plan approval to build a 19-story lab building at 120 Middlesex Avenue, in a market where 1.9 million sq ft of Somerville lab space already sits empty. The application (ZP26-000038) was continued from July 16 to the August 6 Planning Board meeting; it did not appear on the board's September 3 or September 17 agendas, and its outcome is not in our sources yet.

The TransMedics buildout is visible in the permit record: between September 3 and 21 the city issued a run of electrical permits at 188 Assembly Park Drive worth $950,000, $900,000, $895,000, $750,000 and $600,000 for power, lighting, fire alarm, data and security on Levels 3, 10, 11 and 12 and the penthouse, plus plumbing for the upper floors, and lab fit-out work continued at 399 Revolution Drive (city permit data, Sept 21). The UCH-TIF zone covering Assembly Square and East Somerville cleared the Council 10-0 on September 10 and now goes to the state.

The story

The TransMedics deal

The city announced the lease on January 13. Its claims, as the city states them: an estimated $75 million in new tax revenue over ten years, 900 jobs at the site including 600 new positions by 2032, and $230,000 a year in community investments over ten years for Somerville schools, STEM and robotics programs, and the police and fire departments. TransMedics is moving offices, research and development, equipment manufacturing and a flight operations center in, and expects to spend $175–225 million on the buildout with operations beginning by January 2028.

The public side of it: the City Council approved an $18 million tax increment financing agreement, which the city describes as generating four times its value in new revenue; the Massachusetts Life Sciences Center proposed a state performance-based package worth up to $18 million more, tied to the 600 new jobs, workforce development and equipment. Mayor Jake Wilson framed it as fitting "right in here in Somerville with our growing life science hub." Council President and Ward 6 Councilor Lance Davis credited "creative financing like the TIF that the Council approved." 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, and that 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). On August 27 the Council approved a grant of location for Lightpath to run 41 feet of conduit in Grand Union Boulevard next to 188 Assembly Park Drive (item 26-1278) — the kind of housekeeping that follows a fit-out. See The lab glut and the tax base for why one lease carries this much fiscal weight.

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 is new speculative lab space landing in the middle of the glut: Golden told the Council in April that of the city's 10 life science buildings only five are stabilized, and Wilson said conversion to other uses is impractical because of the buildings' limited windows and specialized air handling. Whether the Planning Board approved, continued or conditioned it on August 6 is not in our sources.

The city as landowner and landlord

Assembly Square is also where the city has been buying rather than 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 housing the Assembly Square Fire Station from BioMed Realty, which was liquidating the garage complex. The city had already put $8–10 million into fitting the space out as a fire station and was paying $363,699 a year in rent; OSPCD Executive Director Tom Galligani said buying saves roughly $1 million over 28 years, and Finance Director Ed Bean put first-year debt service at short-term rates at about $175,000 and the 28-year totals at $12.4 million to buy versus $13.4 million to keep leasing (April 9 Council). Scott pressed hard on approving a purchase and sale agreement that had not yet been drafted, then voted for it. On May 28 the Council amended the 2010 Assembly Square District Improvement Financing district to take in the station at 45 Middlesex Avenue and improvements straightening the Middlesex/Mystic Avenue intersection, letting the city borrow short-term at roughly 2.5% instead of 3.5% (May 26 Finance; May 28 Council).

Two other threads run through the neighborhood. The proposed UCH-TIF housing incentive zone covers parts of Assembly Square and East Somerville along East Broadway, McGrath Highway and Assembly Row, and is still in the Land Use Committee — 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, likely on the former Christmas Tree Shop parking lot — see Combined sewer overflows.

What's next

August 6, 2026 — Planning Board hearing on site plan approval for the 19-story lab building at 120 Middlesex Avenue (outcome not in our sources yet; the case has not reappeared on a posted agenda since).
By January 2028 — TransMedics operations begin at 188 Assembly Park Drive after a $175–225 million buildout.
2032 — TransMedics' target date 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 individual tax deal here still needs its own Council vote and state sign-off. See Housing tax-break zone for East Somerville and Assembly Square.