Southborough, MA Zoning Overlays & Bonuses: Density Bonus Law (2026)

Section 174-13.2 governs major residential development, defined in subsection A(1) as the creation of eight or more lots or construction of eight or more dwelling units within an eight-year period. An applicant can take the Planning Board special permit route, which requires a concurrent filing with the Southborough Housing Opportunity Partnership Committee (SHOPC), or build by right as a conventional development without the flexible development option.

The density bonus is tied to affordable units. Subsection E(1)(a) sets the minimum at 12.5% of the total number of dwelling units, and E(1)(b) rounds a fraction of 1/2 or greater up and a smaller fraction down. In return, E(4)(a) reduces the minimum lot area per dwelling unit by the amount necessary, upon approval, to permit up to three additional units for each one affordable unit. Under E(5)(b), the incentive is not available when the developer meets the requirement through the cash contribution method.

Affordable units serve low-income households, defined in E(1)(e) as total household income between 51% and 80% of the median income for the Boston Standard Metropolitan Statistical Area. Under E(2), the units stay affordable in perpetuity to the extent legally possible and in no case for fewer than 50 years, rents and housing costs cannot exceed 30% of targeted gross household income, and not less than 70% of the affordable units are first offered to Town employees and long-term residents.

Subsection F adds a discretionary bonus of up to an additional ten percent from the Planning Board. Middle-income units for households not exceeding 140% of the median family income earn one added lot or unit for each such unit if affordability lasts not less than 10 years. Land preserved on site or off site under a conservation restriction, or deeded to the Town, earns one added unit for each unit the land could reasonably have supported under a conventional plan, and the Critical Resource District bonus is double that number.

Construction is sequenced under E(6)(c): no certificate of occupancy issues for market-rate units until 25% of the required affordable units have one, and no more than 75% of market-rate units receive one until 100% of the affordable units do. Development within a Critical Resource District is exempt under E(8).