A 312-unit apartment building is rising on Lexington's Hartwell Avenue right now. Just a few miles away in Waltham, the same developer just watched a nearly identical proposal get vetoed by the mayor. The contrast says a lot about what makes a town ready for this kind of housing — and what doesn't.

BXP, which calls itself the nation's largest publicly traded office REIT, had proposed converting the Bay Colony office park on Winter Street into multifamily housing. Waltham Mayor Jeannette McCarthy vetoed the rezoning on July 1, and her reasoning came down to one thing: transit. "[The Bay Colony office park rezoning] and its subdistricts have no access to public transportation, bus or rail," she wrote in her veto letter. "Why then is [Bay Colony] included and given the same benefits as [1265 Main St. and Waltham-Weston Corporate Center] when there is no transit-oriented development benefit?"

The Hartwell Avenue site tells a different story: it sits just 0.1 miles from MBTA Route 62 and 0.2 miles from the Minuteman Bikeway. Lexington's Planning Board approved the project in December 2024 under the town's Village High-Rise Overlay district, and it's now the first major residential development approved under the MBTA Communities Act in Lexington — exactly the kind of transit-connected project the law was designed to encourage.

The 347,000-square-foot wood-frame building will hold a mix of unit types — 16 studios, 142 one-bedrooms, 24 one-bedrooms with den, 97 two-bedrooms, and 33 three-bedrooms — with 47 units income-restricted for households earning up to 80% of the area median income, plus about 2,100 square feet of ground-floor retail. Lexington Planning Director Abby McCabe said the town's housing stock currently leans heavily toward single-family homes with three or more bedrooms, and this project helps diversify what's actually available. The building targets Passive House certification and LEED Silver, with all-electric systems and 20 Level-2 EV chargers, and is expected to open by mid-2027.

It's a joint venture between BXP and Northwestern Mutual, which holds the majority stake and secured a $98.7 million construction loan. BXP bought the 5.25-acre site for $21.84 million last June, with Dellbrook JKS managing construction.

Office vacancy along Route 128 sat at 20.3% at midyear — even BXP's own Bay Colony property in Waltham was only 79.7% leased last quarter — pushing landlords across the corridor to convert underused office space into housing instead. Lexington has leaned into that shift hard: since adopting MBTA Communities zoning in 2023, its planning board has approved nine new housing projects totaling more than 1,100 units, including 160 affordable ones.

In Waltham, the City Council still has the power to override McCarthy's veto; two other BXP rezonings the council approved in June remain in effect, with only the Bay Colony portion blocked. In Lexington, residents along Hartwell Avenue should expect construction through mid-2027, with 408 vehicle parking spaces and 504 bike spaces planned once the building is finished.