Councilors seek smaller backyard cottage cap under state ADU law

Items Discussed

Accessory dwelling unit (ADU) zoning to align with state law – Kept in committee

This administration-submitted amendment would bring Somerville's backyard cottage rules into line with state ADU regulations, which Planning Director Dan Bartman said the city is legally bound to follow under the Administrative Procedures Act even though they live in state regulations rather than the zoning act itself. He said the state treats ADUs as a protected use, like churches and schools, that cannot be prohibited in any district. Under the regulations, an ADU may have the same height, width and depth as the principal building on the lot and must follow the setbacks allowed for accessory structures (currently three feet). The main control is a square-footage cap; the administration's draft used a number (roughly 1,500 square feet) chosen because it captured every backyard cottage built since 2022, which Bartman stressed was not necessarily where the city should land.

Committee members broadly agreed the current results—three-level cottages with built-out basements and cross-gable roofs—do not match the one-and-a-half-story cottages promised in the 2019 zoning overhaul. Council President Lance Davis, who chaired the committee during the overhaul, called the state's interpretation "comically ridiculous" as applied to Somerville, noted the city's state senator has said it was not the legislative intent, and said he was willing to "push the envelope" with local limits. He reported the mayor confirmed to him that evening that the 1,500 figure was a placeholder and the administration has no objection to the council lowering it. Councilor Matt McLaughlin offered a partial counterpoint, saying he investigated public testimony about displacement caused by ADU and triple-decker zoning and found that CAAS, the condo conversion board chair and the housing stability office have not seen the surge described; he said three units plus an ADU remains acceptable to him but a full second house does not. Councilor Naima Sait said she supports ADUs but a "triple decker behind a triple decker" would "create a bunch of boxes in our city." Councilor Jesse Clingan asked whether Somerville was caught by rules aimed at suburbs; Chair Ben Ewen-Campen noted the state's own FAQ explicitly addresses triple-decker lots, undercutting that theory.

Ewen-Campen proposed a path forward: set the total square footage at two floor plates of 576 square feet (about 1,150 square feet) instead of three, keep a 1.5-story limit, and ensure basements count toward the total. He acknowledged a builder could theoretically ignore local rules and build a 900-square-foot three-story unit under state standards, but argued few would. Bartman cautioned that any reduction will have a "material impact" on production, noting cottages "happen to be some of the most housing we've had over the last couple years."

Additional points raised:

• Davis doubted developers would let basements count, citing Somerville's history of illegal basement apartments; Bartman said that is largely an enforcement issue and agreed to double-check square-footage exemptions.
• Bartman confirmed existing accessory structures—even nonconforming ones like a garage near a lot line—can be converted to ADUs under the state rules.
• Clingan asked about requiring stormwater retention tanks; Bartman said any requirement must apply equally to the principal structure.
• Sait asked for visuals of ADU placement scenarios; Bartman said a separate accessory-structure cleanup amendment is forthcoming.
• Ewen-Campen and Councilor Ben Wheeler submitted comments during the state's recent regulation comment period; the administration did not.

The chair said he will work with council staff on amendment language. No vote was taken.

Removal of ground story elevation requirements – Recommended to be approved as amended, 4-0

This administration amendment removes the two-foot ground story elevation requirement for residential buildings, allowing ground-level construction to improve accessibility. Bartman said the requirement was stylistic—codified from measurements of existing housing stock—rather than a flood or safety measure, and that raising a building becomes a property owner's choice based on site conditions. Clingan asked what purpose the elevation served; Bartman cited crawl spaces, pipe insulation and groundwater, but no regulatory need. Sait asked how flooding is handled for large developments, citing basement inclusionary units that flooded in her ward; Bartman said engineering's site construction permit addresses stormwater case by case, and sustainability and engineering staff are developing flood-zone elevation requirements.

Ewen-Campen moved to amend the mayor's version to also strike the nonbinding architectural design guidelines (Sections 3.1.15.a.1, 3.2.14.a, 4.1.7.f, 4.2.7.f, 4.3.7.f and 4.4.7.f) that encourage elevated ground-floor units, saying it "seems off" to encourage accessible units while suggesting they be raised. Bartman said planning had no objection. The amendment passed 4-0 by roll call, and the item was recommended as amended 4-0 (Davis had not yet arrived).

Councilor Link's companion ground-story amendment (Section 3.1.7.c) – Kept in committee

A nearly identical proposal from Councilor Jonathan Link, which included the architectural guideline changes now folded into the administration's version. It has not had a public hearing; the chair said he will ask Link how to dispose of it, likely by withdrawal.

Clarify requirements for principal entrances – Recommended to be approved, 4-0

This administration amendment allows a building's main entrance to be on a side wall, provided the ground-floor unit still has a door on the front facade—accommodating new triple-decker designs with side stairwells—and allows entrances on any side of a detached ADU, since state setback rules may place cottages in side or front yards. It also strikes 30-foot ground-story entrance spacing rules in mid-rise districts, which Bartman called an outdated form-based-code artifact producing nonfunctional doors (he had shown the Davis Square Domino's as an example) and variance requests; he said the small business overlay is the better tool for commercial frontage. Ewen-Campen questioned rear doors on cottages near lot lines; Bartman said the building code already limits wall openings near adjacent structures. Sait asked about fire egress (no change to building code requirements) and requested visuals. Clingan raised practical concerns about mail and trespass but concluded flexibility was the important piece.

Routine corrections: parking maximums and affordability terminology – Both recommended to be approved, 4-0

• Parking maximums: fixes drafting and codification errors in a prior large amendment, reflecting the Mobility department's original intent. Bartman said staff reviewed the numbers multiple times.
• Terminology: renames "affordable dwelling unit" to "price restricted dwelling unit" (PRDU) because the state has claimed "ADU" for accessory dwelling units, and standardizes "commercial unit" across the ordinance, leaving room for a future "price restricted commercial unit."

What's Next

• The ground story elevation, principal entrance, parking maximum and terminology amendments go to the full council but will be laid on the table; the chair said final votes cannot occur until the public comment period closes October 30 and the Planning Board issues recommendations. The committee may revisit if public comment warrants.
• The ADU amendment stays in committee. Ewen-Campen will prepare language for a two-floor-plate (≈1,150 sq ft) cap, a 1.5-story limit, and basement-counting or basement-prohibition provisions; he asked members to send other ideas to staff. He said there is no legal deadline but hopes to finish before his term ends in December.
• Link's companion item stays in committee pending his decision.
• Requests for information (McLaughlin, to be sent to the clerk and intergovernmental affairs): a city solicitor opinion on the state ADU law and what Somerville must do to comply; data from Inspectional Services on homes of three units or fewer demolished since the three-family and ADU ordinances took effect and three years prior; data from the Housing Division on condo conversions applied for over the same periods and how many tenants received or did not receive compensation. McLaughlin also asked whether a 25-foot setback claim in state law is accurate.
• Davis requested a review of green score calculations for permeable surfaces given stormwater concerns, and a definitive answer from planning on whether basements can be excluded from square-footage totals.
• Bartman said a forthcoming amendment will clean up accessory structure rules related to ADU placement.