Somerville, MA Accessory Structures: Tiny Homes (2026)
Tiny home rules in Somerville, MA, covering tiny houses on wheels (THOWs), park model RVs, and tiny home on foundation builds, determine where they are legal and how they get permitted.
Key Facts
- Max floor plate
- 576 sq ft
- Max stories
- 1.5 stories
- Max story height
- 12 ft
- Min side/rear setback
- 3 ft
- Dwelling units allowed
- 1 per cottage
- Sprinkler rule
- Required unless corner/driveway/alley lot
Summary
Somerville's zoning ordinance permits one detached Backyard Cottage per lot in the Neighborhood Residence district, capping the accessory building at a 576-square-foot floor plate, 24 feet wide, 32 feet deep, and 1.5 stories under Zoning Ordinance Section 3.1.12. The cottage holds only one dwelling unit and must sit at least 3 feet from the side and rear lot lines.
3.1.12 Backyard Cottage A small floor plate, detached, accessory building type typically providing space for one (1) small dwelling unit, a home occupation, a playhouse for children, or vehicular parking on the same lot as a principal building type. ... Side Setback (min) 3 ft ... Rear Setback (min) 3 ft ... Building Separation (min) 10 ft ... Width (max) 24 ft ... Depth (max) 32 ft ... Floor plate (max) 576 ft ... Story Height (max) 12 ft ... Number of Stories (max) 1.5 stories ... Roof Type Flat, Gable ... Dwelling Units (max) 1
Full Breakdown
Section 3.1.12 of the Somerville Zoning Ordinance defines the Backyard Cottage as "a small floor plate, detached, accessory building type typically providing space for one (1) small dwelling unit, a home occupation, a playhouse for children, or vehicular parking on the same lot as a principal building type." It is permitted by right as an accessory building type in the Neighborhood Residence (NR) district under Section 3.1.6.c, alongside principal building types such as the Cottage, Detached House, Semi-Detached House, Duplex and Detached Triple Decker.
The dimensional table in Section 3.1.12 caps the Backyard Cottage's main massing at a maximum width of 24 feet, a maximum depth of 32 feet, and a maximum floor plate of 576 square feet. The building may rise a maximum of 1.5 stories with a maximum story height of 12 feet, topped by a flat or gable roof, and only one dwelling unit is allowed inside. Placement is tight to the interior of the lot: the minimum side setback is 3 feet, the minimum rear setback is 3 feet, and the cottage must maintain a 10-foot building separation from the principal building on the lot.
Section 3.1.12.f layers design and safety standards on top of the dimensional limits: a three-foot-wide paved walkway capable of accommodating an ambulance cot must lead to the cottage, all utility services must be buried underground, and, by order of the Fire Prevention Bureau, any Backyard Cottage occupied by a permitted residential use must have an automatic sprinkler system unless the lot is a corner lot, has a driveway leading to the cottage, or abuts an alley. These standards took effect November 21, 2023 under Ordinance 2023-23.
Violations & Fines
A Backyard Cottage built beyond the 576-square-foot floor plate, taller than 1.5 stories or 12 feet per story, or sited closer than 3 feet to a side or rear lot line violates Section 3.1.12. The Somerville Inspectional Services Department can stop the work, require removal of the noncompliant structure, or withhold occupancy until the sprinkler and walkway standards are met.
Frequently Asked Questions
Do I need a permit to build a Backyard Cottage in Somerville?
How big can a Somerville Backyard Cottage be?
Does a Backyard Cottage need a fire sprinkler system?
Sources & Official References
Other rules in Somerville
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