Accessory Dwelling Units (ADUs) In Watertown, Massachusetts

Saturday-June 28th-2025-By Mike DelRose Sr.- On August 6, 2024, Massachusetts Governor Maura Healey signed the Affordable Homes Act (Chapter 150 of the Acts of 2024), a significant legislative step to address the state’s housing affordability crisis. A key provision in Section 8 of the Act amends the Zoning Act to allow accessory dwelling units (ADUs) up to 900 square feet to be built by right in single-family zoning districts, meaning homeowners can construct these units without needing special permits or discretionary approvals from local zoning boards. This change aims to increase housing options by enabling property owners to add small, self-contained living spaces, such as in-law apartments or detached units like converted garages, on their existing lots, fostering affordable and sustainable housing solutions. The law, reflects Massachusetts’ commitment to innovative approaches to combat rising housing costs and homelessness, with ADUs seen as a critical tool to meet diverse housing needs.

Potential ADU Locations

To support implementation, the Executive Office of Housing and Livable Communities (EOHLC), in collaboration with the Metropolitan Area Planning Council (MAPC) and Massachusetts Housing Partnership (MHP), has developed model ADU zoning guidelines and a municipal checklist to help cities and towns align local regulations with the new law. The regulations, outlined in 760 CMR 71.00, took effect on January 31, 2025, providing clear definitions and administrative details for ADUs, including exemptions from certain parking requirements near transit hubs. Homeowners must still comply with local building codes and health and environmental regulations, such as those concerning sewerage and water supply, and should consult local planning or building departments for specific property-related questions. The law also opens opportunities for rental income and increased property value, though homeowners are advised to consider potential tax implications and financing options for ADU construction.

In Watertown, MA, the new state law applies directly, allowing ADUs by right in single-family zoning districts, but local zoning bylaws may still impose specific requirements. There is some uncertainty as to whether accessory apartments will be allowed in homes currently containing two units. Historically there have been times where these units were encouraged. Watertown has not yet published updated ADU-specific ordinances in response to the state law, so homeowners should contact the Watertown Planning and Community Development Department to confirm compliance with local zoning, building codes, and permitting
processes. Given Watertown’s proximity to transit hubs like the MBTA bus lines and commuter rail, ADUs may benefit from relaxed parking requirements, enhancing feasibility for urban lots.