Accessory Structures in Boston, MA (2026)
9 verified accessory structures rules for Boston, Massachusetts, sourced directly from the municipal code and official government pages.
Verified from official government sources
ADU Rules
ADUs are now allowed by right statewide in Massachusetts under the 2024 Affordable Homes Act, with a maximum of 900 square feet. Boston cannot require owner-occupancy or special permits for protected ADUs.
Boston ADU (Accessory Dwelling Unit) Rules
Some RestrictionsMass. Gen. Laws ch. 40A, Sec. 3 (Accessory Dwelling Units Allowed As-of-Right in Single-Family Zoning Districts)
No zoning ordinance or by-law shall prohibit, unreasonably restrict or require a special permit or other discretionary zoning approval for the use of land or structures for a single accessory dwelling unit, or the rental thereof, in a single-family residential zoning district; provided, that the use of land or structures for such accessory dwelling unit under this paragraph may be subject to re...
ADU Permits
Boston ADU permits are reviewed under the Boston Zoning Code (BZC) Article 65 and underlying neighborhood districts, with statewide ADU-by-right standards established by the 2024 Massachusetts Affordable Homes Act (Chapter 150 of the Acts of 2024). Detached ADUs under 900 sq ft are allowed by-right in single-family zones statewide, but Boston still requires building, electrical, plumbing, and zoning permits issued by the Inspectional Services Department (ISD).
Boston ADU Permit Requirements
Some RestrictionsADU Impact Fees
Boston does not impose dedicated ADU impact fees. The 2024 Massachusetts Affordable Homes Act prohibits municipalities from charging excessive ADU fees that would render units infeasible. Standard permit fees through ISD apply (building, plumbing, electrical), and Boston's Inclusionary Development Policy and linkage fees do not apply to single-ADU residential additions.
Boston ADU Impact Fees and Linkage
Few RestrictionsADU Owner Occupancy
The 2024 Massachusetts Affordable Homes Act prohibits cities from requiring owner occupancy as a condition of building or renting an ADU. Boston previously required owner occupancy under its ADU pilot but state preemption has removed this requirement for by-right ADUs under 900 sq ft. Owner-occupancy mandates are no longer enforceable on single-family lots.
Boston ADU Owner-Occupancy Rules
Few RestrictionsADU Rental Restrictions
Boston ADUs can be rented as long-term residential units without owner-occupancy under the 2024 Massachusetts Affordable Homes Act. However, Boston's Short-Term Rental Ordinance (City Code 9-14) restricts most ADU short-term rentals: only owner-occupied units can be registered as Home Share or Owner-Adjacent listings. Investor-owned ADUs cannot be used for Airbnb-style rentals.
Boston ADU Rental and Short-Term Restrictions
Some RestrictionsShed Rules
Boston regulates sheds through zoning dimensional requirements in Article 13. Small sheds under 120 square feet may not require a building permit but must meet setback requirements.
Boston Shed & Outbuilding Rules
Some RestrictionsGarage Conversions
Garage conversions to ADUs are explicitly allowed under the 2024 MA Affordable Homes Act by right on single-family zoned lots, subject to building code compliance and permit requirements.
Boston Garage Conversion Rules
Some RestrictionsMass.gov Accessory Dwelling Units — ADU Requirements (incl. converted garage)
The Affordable Homes Act, Section 7 and 8, amended M.G.L. Chapter 40A Section 1A and M.G.L. Chapter 40A Section 3 to allows accessory dwelling units — or ADUs — under 900 square feet to be built by-right in single-family zoning districts. [...] ADUs can be inside an existing home, like converting a basement into an apartment, attached to a primary residence as an addition, or completely detache...
Carport Rules
Carports in Boston need an ISD building permit if attached to the home or over 200 sq ft. Side and rear setbacks follow the underlying zoning district and historic district rules.
Accessory Structures: Carport Rules
Some RestrictionsTiny Homes
Boston does not recognize tiny houses on wheels as legal dwellings. Tiny homes on foundations must meet full 780 CMR building code and minimum zoning unit size. ADUs are separately governed under 2023 reform.
Accessory Structures: Tiny Homes
Heavy RestrictionsLooking for Suffolk County county-wide rules?
County ordinances apply to unincorporated areas and may supplement Boston city rules.
Accessory Structures in Suffolk County →