Somerville's 1,750 sq ft backyard cottage cap: what would change for homeowners
Somerville may cap backyard cottages at 1,750 sq ft and drop today's 24-by-24-foot footprint limit. What's proposed, who objects and what owners should do now.
Mateus MagnoLicensed Construction Supervisor · November 2, 2026 · 3 min read
Somerville is considering a zoning change that would limit backyard cottages by total floor area, with a cap of 1,750 square feet, instead of today's rules of 24 by 24 feet and one and a half stories. It is a proposal, not law. After an October 1, 2026 public hearing, it goes to the Planning Board for a recommendation and then to the City Council for a decision.
If you've been thinking about building a backyard cottage in Somerville, this affects you. The City is rewriting its rules to match the state's ADU law, and one proposed number is getting all the attention: 1,750 square feet. Cambridge Day covered the debate on October 19, 2026.
Remember that this is a proposal, not the current rule. Here's what would change, who objects and what I'd do if you own a lot today.
Current rules vs. the proposal
| Rule | Today | Mayor's proposal, as reported |
|---|---|---|
| Size limit | 24 x 24 feet, 1.5 stories | Total floor area, up to 1,750 sq ft |
| Primary front setback | 60 feet | 10 feet |
| Lot coverage | 60% | 60%, no change |
| Design rules | Cottage-specific standards | Some aligned with the main building |
A 24-by-24 footprint is 576 square feet, so 1,750 is roughly three times that. The article says partly exposed basements and gabled roofs can already push a cottage toward that total. Staff described the number as representative of a typical local backyard cottage.
Why is Somerville changing its backyard cottage rules?
The Massachusetts ADU law took effect in 2025. It requires ADUs to be allowed in any district that permits single-family homes. In Somerville, that means the Neighborhood Residential and Urban Residential districts, about 60% of the city's land. Size and design rules can't be stricter than those for the main building, and the City can't add occupancy or income rules.
The state's protected size is 900 square feet or half the main house, whichever is smaller, and planners note towns can allow more. Somerville's proposal is nearly double 900.
Who supports it and who objects
- City planners say cottages are in high demand, help families live near each other and offer relatively affordable standalone homes.
- Councilor Ben Ewen-Campen says the Council still has to decide whether to lower the total, and has to balance state law with what he calls Somerville values.
- Attorney and former councilor Bill White argues a large cap won't help renters and could encourage condo development. He proposed a 900-square-foot cap and common ownership of the cottage and main house. That proposal expired without a vote, and he plans to resubmit it this fall.
- Residents at the October 1 hearing spoke both ways, with concerns about size and lost rentals, and support from people who want to build for themselves.
What happens next
- Written public comment closed on October 30, 2026 at noon.
- The Planning Board reviews the amendments and makes a recommendation.
- The City Council makes the final decision. The number could change along the way.
What I'd do if you own a lot in Somerville
- Don't design to 1,750 yet. Start from what's allowed today, and only count on a change once it passes.
- Get a survey. Setbacks, lot coverage and access usually decide what fits. My Somerville backyard ADU map is a good first look.
- Bigger isn't automatically better. A larger cottage costs more to build and may need a bigger foundation and utilities. See what an ADU costs in Massachusetts and backyard ADU basics.
- Plan for the energy code. A new cottage is new construction, and Somerville's code requires it to be all-electric or wired for it. More in my post on all-electric costs.
Thinking about a backyard cottage?
You can try three designs in my ADU Studio, or book a free walkthrough. I'm Mateus, a licensed builder based in Davis Square, and I'll send a written line-item budget, usually within 48 hours.
Frequently asked questions
How big can a backyard cottage be in Somerville?
Under current zoning as reported in October 2026, a backyard cottage can be up to 24 by 24 feet and one and a half stories. A proposal would change that to a total floor area cap of 1,750 square feet, but it has not been adopted.
Is the 1,750 square foot cap law in Somerville?
No. It is a proposed zoning amendment. The Planning Board makes a recommendation, and the City Council makes the final decision.
Where are ADUs allowed in Somerville?
State law requires ADUs wherever single-family homes are allowed. In Somerville, that means the Neighborhood Residential and Urban Residential districts, about 60% of city land.
Can Somerville require a backyard cottage to be affordable?
No. The state law bars occupancy requirements, including income limits, so the City can't set affordability rules for these units.
Planning work near Somerville? See the towns I work in, with local permit notes, and how I price work.
Mateus Magno founded Magno & Co in 2020. He is a licensed Massachusetts Construction Supervisor (CS-123658), registered Home Improvement Contractor (HIC #220484) and certified Lead-Safe Renovator Supervisor who has renovated and managed over $5 million in projects across Greater Boston.
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