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Backyard cottages, ADUs and lot splits

Updated September 22, 2026

What's happening

The administration's rewrite of Somerville's backyard-cottage rules to match the 2024 state ADU law is finally filed. Mayor Jake Wilson filed it September 2 as item 26-1336, with an attachment titled "PADU Compliance Amendment 09.08.2026," and on September 10, as one of a package of zoning amendments, and the Council referred it to the Land Use Committee for a joint public hearing with the Planning Board on Thursday, October 1 at 6:30 p.m. (hearing notice; Sept 10 digest). The amendment touches Sections 3.1.3, 3.1.6, 3.1.8 through 3.1.13, 3.1.16 and 3.2.6 "to align with State Law regarding protected accessory dwelling units," and Intergovernmental Affairs Director Amanda Najeeb Williams pitched the package as mostly "tidying up." Planning staff had promised it "after summer recess" on May 21; its arrival is what the committee said it was waiting for before taking up the four citizen petitions from former Councilor Bill White and At-large Councilor Kristen Strezo's expansion proposal, all held since spring. The text itself is not in our sources yet, so whether it addresses the 1,500 sq ft stacked cottages and the lot-split pattern, or only terminology, is the question for October 1.

Meanwhile the permits keep coming. Between September 3 and 21 the city's permit data showed cottage or ADU activity at 26 distinct addresses, 41 records in all: the three identical two-bedroom "Detached Cottage" applications at 11 Rush St, 65 Derby St and 13 Fiske Ave and the 46 Dickinson St garage conversion are still under review; new filings landed at 66 Farragut Ave, 29 Pennsylvania Ave, 7 Woodbine St and 17 Fremont Ave (an accessory building converting to an ADU); certificates of occupancy issued for cottages at 22 Spring Hill Terrace and 37 Kingston St; and 5 Wilton St filed the pattern this page is about, a $1.05 million three-unit building plus a $380,000 cottage on one lot. A $1,566,964 permit at 42 Ten Hills Rd adds an attached unit "as allowed by right" (city permit data via Citizenserve, Sept 21). The Sept 22 update added an issued foundation permit for a cottage at 17 Oak St, moved 54 Belmont St, a gut renovation that converts a barn into an attached ADU, to approved-awaiting-payment, and showed the 66 Farragut Ave filing as a vertical permit taking a two-unit house to three, still under review. Earlier, a 79 Moreland St cottage permit was re-labeled "Now PADU Not BYC," meaning the builder switched from the city's backyard-cottage rules to the state's protected-use ADU rules. On Aug 5 the ZBA heard a lot-split special permit for 17 Monmouth St, a National Register property in the NR district (agenda); the outcome is not in our sources yet. A statewide vote is coming too: ballot Question 7 on November 3 would allow single-family homes by right on any residentially zoned lot of 5,000 or more square feet with 50 feet of frontage and public water and sewer, subject to "reasonable" local rules (city sample ballot).

The story

The 2019 rules and the eight-condo pattern

The zoning ordinance defines a backyard cottage as "a small floor plate, detached, accessory building type typically providing space for one small dwelling unit" and caps it at a 576 sq ft floor plate, 24 by 32 feet, 1.5 stories, one dwelling unit. A lot split is "the division of a lot into two smaller lots" and, under Section 10.1.1, needs Site Plan Approval, or a special permit if the lot is on the state or national historic registers.

What that produces on the ground is the complaint. White told the joint Land Use-Planning Board hearing on April 16 that developers buy an older house, split the lot, demolish, and build a three-unit building plus a roughly 1,500 sq ft cottage on each half, achieved by stacking the floor plate over three levels including a finished basement. Result: up to eight luxury condos, zero affordable units, on what was one lot. The permit data shows the template: 17 Hudson St has a three-unit building on Lot A, another on Lot B, and a cottage as "Unit D"; 16 Moreland St has triple-decker foundations on Lots A and B plus a cottage; 112 Albion St has two cottage foundations, 112 D and 112 I. Councilor Ben Wheeler raised the same worry on Jan 8: developers "interpreting ADU rules to split what might otherwise be a single building that would be subject to inclusionary zoning... into two smaller structures that each avoid the threshold."

The state law collision

The Affordable Homes Act of 2024 protects accessory dwelling units, "PADUs," from local rules that would nullify them or impose "excessive costs." Senior Zoning Review Planner Joshua Manion walked Land Use through the damage on March 19. Somerville's code says "backyard cottage" where the state says ADU, "principal building" where the state says "principal dwelling," and uses "ADU" to mean affordable dwelling unit. Staff first assumed the law did not apply because Somerville has no single-family district, but the state regulations cover any district that permits single-family homes, which sweeps in both NR and UR. Worst of all, a PADU may use the most permissive dimensional standard for any building type in its district, and NR allows triple-deckers, so a three-story ADU is arguable. Manion said developers are "kicking the tires" on such configurations, including one 10-foot-deep cottage staff call "an ant farm." The Attorney General wants reasonableness judged lot by lot; the city solicitor says ISD can make those calls but cannot invent a waiver process. Ward 3 Councilor Ben Ewen-Campen, the Land Use chair, summarized it on March 26: "It's just not the outcome that was intended," and "quite frustrating."

Strezo's expansion

Strezo went the other direction. Her amendment (item 26-0234), introduced Feb 12 with co-sponsors Will Mbah, Lance Davis and Naima Sait, would allow two full stories instead of 1.5, widen the footprint to 40 feet to fit prefab and modular models, enlarge the floor plate, and add looser setbacks for converting carports and other existing structures, all to "lower regulatory barriers to production." At the March 19 hearing supporters Joshua Mitchell and Aaron Weber praised the flexibility; White, Meredith Porter, Tori Antonino and Jane Bester warned of developer exploitation and lost green space. Strezo asked that no substantive discussion happen before mid-May, and none has. Separately, her Jan 22 order to study incentives for owner-occupied ADUs, modeled on New York's ADU Plus One and Salem's tax break for below-market ADU rents, went to the housing committee.

White's four petitions

White's petitions, filed with groups of registered voters and referred March 12, would: move lot splits to a ZBA special permit with public notice (26-0327); apply the 20% inclusionary requirement across both lots when a split yields five or more units (26-0328); cap cottages at 900 sq ft or half the main house, matching state law (the two digests swap file numbers 26-0329 and 26-0330 between this and the next item); and make cottages accessory to the principal dwelling so they cannot be sold as separate condos. Planning Board member Amelia Aboff thanked White for raising lot splits, saying she had not known it was happening. Testimony April 16 was long and split: Kate Byrne, Wig Zamore, Bill Shelton and others described demolished homes and displaced working-class neighbors and argued Somerville has an affordability crisis, not a housing crisis; Weber, Julian Bradley Lewis and Sarah Dunbar said the changes would cut production and that compliant lot splits should stay administrative.

Staff came back on May 21 opposed to three of the four. Deputy Director of Planning, Preservation and Zoning Fiona DiMartino said the zoning ordinance does not regulate condominiums and the state ADU law bars regulating ownership. On inclusionary-by-lot-split, the Council's land use analyst Samantha Carr and staff cited the state uniformity clause, a possible conflict with MBTA Communities compliance (affordability requirements were removed from NR in 2023 for that reason), and feasibility: a requirement on 2-4 unit projects would likely make that kind of development "cease entirely" during the lowest housing production in decades. On ZBA review, staff said lots must already be 100% compliant and are researching non-zoning ways to give neighbors notice. Only the 900 sq ft cap got a warm reception, with the caveat that it does not limit height and could make cottages "uneconomic" without massing changes.

The councilors split too. Davis said the near-1,500 sq ft cottages are "absolutely not consistent" with what he voted for as chair in 2019 and that neighborhood impact should outweigh a marginal housing gain. Councilor Jesse Clingan said lot splits plus cottages are producing eight-unit, multi-million-dollar developments that skirt affordability rules. Ewen-Campen said he is "struggling," recounted a developer posting an AI video of a missile destroying a demolished Albion Street garage ("despicable"), but warned that ZBA hearings for compliant splits would recreate a "pay-to-play" system: if minimum lot sizes are wrong, change them directly. Councilor Matthew McLaughlin backed the 900 sq ft cap and state consistency but opposed the condo ban and "changes designed to prevent ADUs from being built at all." All four items were held in committee. Ward 2 Councilor JT Scott added on May 28 that site plan approval for lot splits is supposed to require a neighborhood meeting but has been administratively delegated.

The dormer carve-out

When the committee advanced the dormer reform on May 7, it deliberately amended Table 3.1.13 to mark gable and shed dormers "N" for backyard cottages, so the new full-width dormers cannot make cottages bigger before the cottage rules are settled. That exclusion survived into the June 25 ordinance; the July 9 code text still shows the old "P" and has not caught up.

What is actually being built

The Citizenserve export for Aug 22 to Sept 2 lists roughly two dozen active cottage or ADU permits across all seven wards: issued construction permits this year at 16 Warwick St (March 2), 54 Adams St (May 15), 72 Jaques St (May 26), 26 Clark St (June 8), 8 MacArthur St (July 27), 79 Moreland St (Aug 3), 163 Morrison Ave (Aug 31) and 46 Mount Vernon St (Sept 1); a 45 Fremont St foundation permit specifying a 576 sq ft floor plate "per SZO 3.1.12"; and conversions of a barn (54 Belmont St) and a third floor (114 School St). Fees on the new modular applications are identical ($958 foundation, $8,180 vertical), consistent with one builder filing three at once. Council President Davis flagged on May 21 that developers may rush projects in before any amendment passes and asked legal staff to close any transition loophole.

What's next

  • October 1, 2026, 6:30 p.m. — joint Land Use / Planning Board hearing on the state-ADU alignment amendment, alongside the rest of the administration's package; written comment by 4 p.m. that day. See the zoning tracker.
  • After the hearing — Land Use can restart the White petitions (26-0327 through 26-0330) and Strezo's expansion (26-0234), which were held pending this filing.
  • Staff deliverables requested May 21 and still owed: written opinions on the ZBA lot-split and inclusionary petitions, a uniformity-clause analysis, a comparison of how other Massachusetts cities review lot splits, and an economic test of a 900 sq ft cap with adjusted massing.
  • November 3, 2026 — Question 7, the statewide single-family-by-right measure.
  • December 31, 2026 — Land Use chair Ben Ewen-Campen leaves the Council (Three Council seats turn over).
  • Aug 5: ZBA special permit for the 17 Monmouth St lot split (outcome not in our sources yet). Pending permits to watch: 11 Rush St, 65 Derby St, 13 Fiske Ave (under review), 46 Dickinson St garage conversion, 54 Belmont St barn ADU.
  • The dormer change and overlay are on affordable housing overlay; board dockets are on what's before the boards.