Somerville is working to align local zoning with a state law that changes how the city will restrict the size of accessory dwelling units (ADUs), including what Somerville has termed backyard cottages. Instead of setting limits in height, width, and depth, the city will use floor area to maintain the scale of the cottages. But with a maximum of 1,750 square feet, the city is proposing a size nearly double what the state suggests.
“The law offers a 900-square foot size maximum … but it does further allow municipalities to set a more permissive limit,” Senior Planner Kortney Cena said at an Oct. 1 public hearing.
Recent amendments proposed by Mayor Jake Wilson’s office would adjust the current zoning standards to fit with state requirements, relaxing design restrictions and allowing a generous square footage limit to encourage much-needed housing supply. Now, the city council must consider what size is appropriate for an ADU, within the limited terms Somerville can regulate them.
Currently, the city allows ADUs up to 24-feet by 24-feet and one-and-a-half stories, but features like partially-exposed basements and roof forms that increase habitable space can result in backyard cottages closer to the proposed 1,750-square footage. While city staff described the proposal as “representative of the typical backyard cottage” in the area, many residents consider those current standards to be too large.
“The conversation the council is going to have is if we want to turn down the knob on the overall square footage, given the fact that [the state] has taken away one of the most logical ways for us to regulate this,” Councilor Ben Ewen-Campen said in a phone interview. Ewen-Campen will shift to the state legislature next year.
State law limits options for city
The state law, which went into effect last year, requires that ADUs be allowed in any zoning district that allows a single-family residential dwelling. For Somerville, that includes both the Neighborhood Residential and Urban Residential districts, which make up about 60 percent of its land space.
The dimensional and design standards for ADUs in those areas cannot be more restrictive than they are for the principal building. This means that Somerville cannot regulate an ADU’s size by width, depth, or number of stories to be more restrictive than what is permitted for the primary building on the lot. Instead, the city can regulate size based on the gross floor area.
For backyard cottages, the proposal would establish a maximum total floor area of 1,750 square feet. That’s three times the allowed floorplate square footage under current zoning, which allows a 24-feet wide by 24-feet deep structure of one and a half stories. The new proposal would permit the same sizing for ADUs on lots with triple decker buildings. However, additions like partially-exposed basements and gabled roofs have resulted in backyard cottages closer to the proposed 1,750 square footage.
In addition to the maximum square footage limit, the proposal decreases the primary front setback from 60 feet to 10 feet. “We expect that changing that setback means we’ll see less issues of lots that are uniquely shaped or lots with multiple frontages,” Cena said. The proposal also simplifies the description of a backyard cottage and relaxes some design standards to align with the principal structure.
In developing the proposal, city staff conducted workshops with various departments, an analytical report of backyard cottages built in Somerville between February 2022 and July 2026, interviews with industry experts and focus groups with architects and developers.
“We learned that backyard cottages of their current size are in high demand in Somerville,” Cena said at the hearing. She described them as one example of residential projects that remain in high demand during a time of stunted development growth. “They allow multi-generational living and allow new families or working couples an option that is a standalone unit in the city that’s a little bit more affordable than other options.”
However, Somerville has no way to dictate the affordability of backyard cottage units under the state law, which denies any requirement for occupancy, including income. With the city’s limited purview over certain zoning standards, residents are concerned the buildings allowed under the proposal will be far from what most consider a backyard cottage and could hurt renters by encouraging condo-style development.
Residents fear ADUs will mean fewer rental units
“Everyone who rents in the city should understand that, unless you have money for a down payment for a luxury condominium, [this proposal] does not help you,” attorney and former city councilor Bill White said in a phone interview. “If you currently rent and your building is sold, it will hurt you.”
Earlier this year, White proposed amendments to limit backyard cottages to 900 square feet maximum and ensure ADUs have the same owner as the principal structure on a property. Those amendments did not receive a vote before the city council’s summer recess and expired. After reviewing the mayor’s amendments, White plans to resubmit his proposal this fall.
The mayor’s amendments will create more units, White says, but “What kind of units? Luxury condominium units. At what cost? The removal of rental units.” He fears that developers will buy properties and replace the existing residential building with up to three luxury condominium units, along with a fourth backyard cottage unit. White is currently the attorney for a land court lawsuit over a property with this kind of proposed development.
“If you do that continuously in a community… you’re skewing your population in the future towards a very different background,” White said.
Many residents during public comment raised concerns about the size of ADUs and the threat to existing rental units. “For an accessory building, it pretty much looks like a house,” resident Fanny Herisson said. “The situation is completely out of control,” long-term renter Jane Bestor said. A few residents spoke in favor of the amendments, encouraging the effort to add to the city’s housing supply and highlighting neighbors with plans to build ADUs for themselves, “not just selling out,” as Joshua Michel described.
Some residents were concerned that adding a backyard cottage would decrease green space, though the maximum coverage allowed for a lot, 60 percent, does not change with an added structure.
City council vote to come
The mayor’s ADU proposal was among five amendments to the zoning ordinance. “The work involves identifying where state requirements override existing local restrictions and where Somerville still has policy choices,” Planning Director Dan Bartman said in an email. “The goal is to give residents and applicants expected standards and give staff a consistent basis for administering them.”
In terms of increasing housing supply, city staff said the ADU amendments are just one effort, alongside affordable housing projects and support for residents facing displacement. “Adding housing and helping residents remain in Somerville are both priorities,” a city spokesperson said over email. “Backyard cottages can provide another housing option for families, smaller households, and people who want to live near relatives.”
The city will accept written public comments until Oct. 30 at noon. Then the planning board will review the amendments and make a recommendation to the city council, which will ultimately make a decision on the proposal.
“Housing is housing. To adapt to changing housing needs, you do need to create more permissiveness,” Ewen-Campen said. “What we’re trying to do is deal with the facts of the state law and then also make sure that we are enacting Somerville values.”
A stronger
Please consider making a financial contribution to maintain, expand and improve Cambridge Day.
We are now a 501(c)(3) nonprofit and all donations are tax deductible.
Please consider a recurring contribution.