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Massachusetts ADU Law 101

Written by Alex Navarro | March, 2025

Governor Healey officially signed the Affordable Homes Act into law on August 6, 2024; a significant piece of legislation also known as the Housing Bond Bill. This landmark law aims to address the pressing issue of housing affordability and availability across the state. One of the key components of the Affordable Homes Act is found in Section 8, which introduces important amendments to the existing Zoning Act. These amendments specifically allow for the construction of Accessory Dwelling Units (ADUs) by right in areas designated as single-family zoning districts. This means that homeowners in these districts can now build ADUs on their properties without needing to go through a lengthy and complicated approval process.

MA ADU Code:

An Additional Dwelling Unit Must:

  • Maintain a separate entrance, either directly from the outside or through an entry hall or corridor shared with the principal dwelling sufficient to meet the requirements of the state building code for safe egress.
  • Be either no larger than half the gross floor area of the principal dwelling or 900 square feet, whichever is smaller.
  • Meet municipal restrictions, including, but not limited to, additional size restrictions and restrictions or prohibitions on short-term rentals.

Towns Can:

  • Require Site Plan Review
  • Enforce Title V Requirements
  • Have Setbacks and Height Restrictions
  • Regulate Short-Term Rentals

Towns Cannot:

  • Require Owner Occupancy
  • Require a Special Permit for use or rental
  • Require more than 1 Parking Space
  • Require ANY Parking within .5 miles of a commuter rail station or bus station

While the law provides this new right, it also grants each municipality the authority to impose certain limited restrictions on the development of ADUs, ensuring that local needs and concerns are taken into account. As these ADUs are permitted by right, the building inspector in each municipality will serve as the primary point of contact for homeowners seeking permits, streamlining the process and making it more accessible for residents looking to expand their living spaces or provide additional housing options. This change is expected to have a significant impact on housing availability, offering more flexible living arrangements and potentially easing the housing crisis in many communities.

Keep in mind that each town may already have, create or modify their own bylaws which will could modify the approval process or steps needed in order to get an ADU. For example, in West Newbury and other towns that have a majority of homes with septic systems, the health department may be the first stop as a dwelling with a bedroom cannot be added unless the septic can take on the additional capacity. Modifications or a new septic may be required to get approval in some situations.