ADU rules in Lynn, MA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Lynn allows one accessory dwelling unit by right on single-family lots, adopted February 11, 2025 under the state Affordable Homes Act. An ADU may not exceed 900 square feet or 50% of the main home's floor area.
Lynn amended its zoning on February 11, 2025 to permit ADUs, matching the statewide 2024 Affordable Homes Act. Under the 2025 Lynn Zoning Ordinance (Section 9.B), one ADU is allowed as of right in single-family districts, within the home or an accessory structure; a Special Permit is needed for more than one. An ADU may not exceed the lesser of 900 square feet or 50% of the principal dwelling's gross floor area, and a detached ADU up to 15 feet tall follows accessory-structure dimensions. One parking space is required unless the lot sits within a half-mile of a commuter rail, subway, ferry, or bus station. ADUs cannot be rented short-term (under 28 days) or occupy RVs or structures on wheels.
Lynn cannot deny a conforming by-right ADU. Building an ADU without permits draws standard 780 CMR enforcement; renting an ADU for under 28 days violates the ordinance's short-term-rental prohibition.
Other ordinances people look up for this city. Green dot = verified primary-source excerpt.
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