Chelsea, MA Accessory Structures: ADU Rules (2026)
ADU rules in Chelsea, MA, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- State Law
- Affordable Homes Act §8 (Feb 2025)
- Max Size
- 900 sq ft or 50% of principal dwelling
- Allowed
- By right in single-family zones
- Local Ordinance
- Draft under Planning Board review (2025)
Summary
ADUs are now allowed by right in Chelsea under Massachusetts Affordable Homes Act (Ch. 150, Acts of 2024, §8, effective Feb 2, 2025). Max 900 sq ft or 50% of principal dwelling. Chelsea's Planning Board was developing a local ADU ordinance in early 2025 to implement the state mandate, with design review retained.
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 reasonable regulations, including, but not limited to, 310 CMR 15.000 et seq., if applicable, site plan review, regulations concerning dimensional setbacks and the bulk and height of structures and may be subject to restrictions and prohibitions on short-term rental, as defined in section 1 of chapter 64G.
Official source re-checked September 8, 2026: the cited page had not changed since it was quoted.
Full Breakdown
The MA Affordable Homes Act preempts local ADU bans in single-family zoning districts. Chelsea previously did not allow ADUs under its zoning ordinance. A draft local ADU ordinance was under review by the Chelsea Planning Board as of January 2025, proposing to allow ADUs by right in any district permitting single-family homes, max one per parcel, subject to design review. No additional parking required within 0.5 miles of MBTA transit stations; 1 space required beyond that distance.
Violations & Fines
Building permits required. Non-compliant ADUs face zoning and building code enforcement.
Frequently Asked Questions
Can I build an ADU on my property in Chelsea?
What are the size limits for an accessory dwelling unit in Chelsea?
Sources & Official References
Other rules in Chelsea
How Chelsea compares: Easiest Cities to Build an ADU·Compare Chelsea to another location·View the Massachusetts accessory structures overview
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ADU Rules in Nearby Cities
How other cities in this county handle adu rules.