Massachusetts ADU Law Explained: What Homeowners Need to Know

Can Massachusetts homeowners now build an accessory dwelling unit on their property?In this special episode, originally recorded for Married to Real Estate at Westford Community Access Television, Mary Foerster and Mary McCauley interview Massachusetts State Representative James “Jim” Arciero about the state’s new accessory dwelling unit law and its potential impact on homeowners, families, municipalities, renters and real estate investors.The Massachusetts Affordable Homes Act made qualifying accessory dwelling units available by right in single-family zoning districts. Under the statewide law, an ADU may be located within a home, attached to an existing residence or built as a detached structure on the same property. State law generally defines a qualifying ADU as being no larger than 900 square feet or half the gross floor area of the principal dwelling, whichever is smaller.Representative Arciero explains why the state changed the previous approval system, how long special-permit processes could take, and why legislators viewed ADUs as one tool for addressing Massachusetts’ housing shortage.The conversation also explores the people who may benefit most from ADUs, including:Older adults who want to age in placeFamilies caring for relatives with disabilitiesYoung adults struggling with housing affordabilityHomeowners seeking rental incomeFamilies interested in multigenerational livingInvestors looking for additional housing opportunitiesMary, Mary and Representative Arciero also address some of the more complicated questions surrounding ADUs, including septic capacity, local permitting, construction costs, public safety, neighborhood concerns, owner-occupancy requirements and the role of individual cities and towns.Massachusetts began allowing qualifying ADUs by right statewide in February 2025 following the 2024 Affordable Homes Act.In This EpisodeWhat qualifies as an accessory dwelling unitWhat “by right” means for Massachusetts homeownersWhy the previous special-permit process created barriersWho may benefit from building an ADUHow ADUs can support aging in placeHousing options for family members with disabilitiesADUs as potential sources of rental incomeHow Massachusetts is responding to its housing shortageAttached, detached and interior ADU optionsThe statewide 900-square-foot standardWhen a local special permit may still be requiredSeptic system and Title 5 considerationsConstruction costs and financing resourcesPublic-safety benefits of legal, permitted housingCommunity concerns about density and neighborhood characterCommercial-to-residential property conversionsThe future of ADU construction across MassachusettsGuest BioMassachusetts State Representative James “Jim” ArcieroJames Arciero is the Massachusetts State Representative for the 2nd Middlesex District. He has served in the Massachusetts House of Representatives since 2009 and represents Westford, Littleton and part of Chelmsford.Representative Arciero previously served as House Chair of the Joint Committee on Housing and played an important role in conversations surrounding housing production, accessory dwelling units and the Massachusetts Affordable Homes Act.He is a graduate of Westford Academy and holds a bachelor’s degree from the University of Massachusetts Dartmouth and a Master of Public Administration from Suffolk University.About the Co-HostsMary FoersterMary Foerster is a real estate professional and the host of Real Estate Connections, a podcast focused on real estate decisions, housing transitions, aging in place and the professionals who help people navigate important life and property changes.Mary McCauleyMary McCauley is a Massachusetts and New Hampshire real estate professional and one of the co-hosts of Married to Real Estate. Her work combines real estate expertise with a strong commitment to the Westford community.Episode CreditThis conversation was originally recorded for Married to Real Estate at Westford Community Access Television and is being shared as a special episode of Real Estate Connections.Send us Fan MailThis episode is intended for informational purposes only and does not constitute financial or investment advice.