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Backyard cottages, ADUs and lot splits

Updated November 10, 2026

What's happening

On Thursday, November 5, the Planning Board and the Land Use Committee held a joint Zoom hearing, starting at 6:30 p.m., on four zoning amendments from former Alderman Bill White. They would rein in backyard cottages, but from the opposite direction to the mayor's amendment (Cambridge Somerville Independent, Nov 1). What happened at the hearing isn't in our sources yet. Somerville YIMBY lists the amendments as items 26-1509 through 26-1512 and calls them a resubmission of White's spring amendments (Somerville YIMBY, Nov 4). White, who served 24 years, and other residents say cottages are being built too big and with no affordable units. His proposals would:

  • make a cottage ancillary to the lot's main building and cap it at 900 sq ft
  • require transparency when a lot is split
  • require approval for a lot split, with a chance for public comment
  • attach an affordability requirement to lot splits

The mayor's state-ADU amendment is item 26-1336. Somerville YIMBY wrote November 4 that Land Use proposed in October to amend it to a 1,152 sq ft maximum for detached ADUs. That's two of Ward 3 Councilor Ben Ewen-Campen's 576 sq ft floor plates, down from the administration's 1,750. The item was before the committee October 29, along with At-large Councilor Jonathan Link's level-entry item (26-1373), under an attachment titled "PADU Compliance Amendment." Legistar still hasn't posted any actions. So our sources don't have the vote count, or whether the 1.5-story limit and counted basements survived (Legistar). YIMBY calls 1,152 sq ft "reasonable" and is asking supporters to back 26-1336 and oppose White's four items. It also cites the state's ADU tracker: at least 43 detached ADUs approved in Somerville since the start of 2025.

When the committee kept the item on October 15, Ewen-Campen, the chair, said he would draft the cap: two 576 sq ft floor plates, a 1.5-story limit and basements counted (Council Digests summary of the Oct 15 meeting, emailed Oct 16). That's above the state's 900 sq ft floor. Planning Director Dan Bartman said the administration chose 1,750 sq ft because it covered every cottage built since 2022, "not necessarily where the city should land." On October 18 Mayor Jake Wilson said he wants the cap cut so the city doesn't end up with "gigantic houses in people's backyards" (Boston Globe).

Bartman laid out what the city can't change. State regulations make the ADU a protected use that no district can prohibit, and he said the city is bound by them even though they aren't in the zoning act itself. An ADU may match the main building's height, width and depth and use the three-foot setbacks allowed for accessory structures. Existing garages and sheds can be converted even when they don't conform to current zoning. The square-footage cap is the main lever the city has. Bartman warned that any cut will have a "material impact" on production, since cottages "happen to be some of the most housing we've had over the last couple years."

The committee mostly agreed that three-level cottages with built-out basements aren't the 1.5-story cottages the 2019 overhaul promised:

  • Council President Lance Davis, who chaired Land Use during the overhaul, called the state's reading "comically ridiculous" for Somerville. He's willing to "push the envelope," but doubts developers will let basements count.
  • Ward 1 Councilor Matt McLaughlin said the Community Action Agency and the Office of Housing Stability haven't seen the surge in displacement residents describe. Three units plus an ADU is fine with him; a full second house isn't.
  • Ward 5 Councilor Naima Sait said a "triple decker behind a triple decker" would "create a bunch of boxes in our city."
  • Ewen-Campen conceded a builder could ignore local rules and put up a 900 sq ft three-story unit under state standards, but argued few would. He hopes to finish before his term ends in December.

McLaughlin asked for a city solicitor's opinion on what the state law requires. He also wants data on demolitions of small homes, condo conversions and tenant relocation pay. Davis wants a definitive answer on whether basements can be left out of the square footage.

The story

The 2019 rules and the eight-condo pattern

The zoning ordinance caps a backyard cottage at a 576 sq ft floor plate, 1.5 stories and one unit. A lot split needs only Site Plan Approval. At the joint hearing on April 16, White described what that produces. Developers split an older lot, tear down the house, and put a three-unit building plus a cottage of about 1,500 sq ft on each half. That's up to eight luxury condos where one house stood, none of them affordable. Permit data shows the pattern at 17 Hudson St, 16 Moreland St, 112 Albion St and 5 Wilton St. At 5 Wilton, a $1.05 million three-unit building and a $380,000 cottage share a lot. At 13 Clyde St, near Magoun Square, occupancy certificates were sought on September 20 for two three-unit buildings and a backyard cottage. On October 7 Fombelle Design applied for occupancy at 146 Jaques St, Winter Hill, for a newly built backyard cottage and for altered condos on the same lot (city permit data). The Globe found "cottages" of close to 1,800 sq ft selling as condos for more than $1.3 million. White says the city has lost 470 rental units in two- and three-family buildings since 2022.

Builders are already invoking the state law. A $1,566,964 permit at 42 Ten Hills Rd adds an attached unit "as allowed by right." On October 7 the city issued a permit at 54 Belmont St, Spring Hill, estimated at $1,373,500. It covers a gut renovation, additions, a full basement foundation and conversion of the barn into an attached ADU. The filing says the property "will remain a single-family residence with an attached ADU and is not proposed as a two-family dwelling."

YIMBY's counterexample is 192 Washington St., where a new triple-decker and a cottage went up. The cottage is only about 100 sq ft smaller than the average of the other three homes. YIMBY's argument is that every family that buys there is one fewer family bidding on an existing Somerville home.

The state law collision

The Affordable Homes Act of 2024 protects ADUs from local rules that would nullify them or impose "excessive costs." State rules (760 CMR 71) require one ADU by right in the Neighborhood Residence and Urban Residence districts, with dimensional standards no stricter than those for the main house. They also bar the city from requiring costly underground utilities. On March 19 staff told Land Use that a protected ADU can borrow the most permissive standard in its district. That would make a three-story ADU arguable wherever triple-deckers are allowed. Ewen-Campen told the Council on October 8 that state and city lawyers share that reading: "It's frankly bizarre." State Sen. Pat Jehlen, who voted for the law, told the Globe nobody intended "to put three-deckers behind three-deckers." The state housing office answered that none of the nearly 2,100 ADU permits approved statewide since January 2025 is three stories.

At the October 1 joint hearing staff listed what 26-1336 does:

  • dimensions measured "per principal building"
  • a front setback cut from 60 feet to 10
  • garage conversions
  • one main building and one ADU per lot

The typical cottage since 2022 has a 24-by-24-foot footprint, a basement, a first floor and a half story, and stands up to about 30 feet tall. Most speakers opposed the amendment.

The opposition's case

White started the fall fight in a Sept 30 Somerville Times commentary, and former Councilor John M. Connolly joined him (Somerville Times, Oct 1). In an Oct 14 commentary, White argued that state law caps a protected ADU at half the main house's floor area or 900 sq ft, whichever is smaller. He said it allows three stories only 20 feet from the rear lot line. If he's right, the "align with state law" pitch oversold what the state requires. Our sources don't settle it, which is why McLaughlin's solicitor's opinion matters.

Ed Woll, a Davis Square Neighborhood Council member, wants four things (Cambridge Day, Oct 27):

  • a ban on lot splits where an ADU is allowed
  • the 900 sq ft limit
  • all-electric ADUs
  • one affordable unit in five on lots of five or more units

Jehlen, who leaves the Senate in January, made the case against demolitions in a November 4 op-ed (Cambridge Somerville Independent). Her Somerville example: a multifamily sold two years ago for $710,000 was torn down for four condos priced at $925,000 to $1.4 million each, "more housing, but fewer units available for people with modest incomes." She doesn't name any of the pending amendments.

The other petitions

At-large Councilor Kristen Strezo's amendment (26-0234) goes the other way, with two full stories and a bigger footprint. It has sat at her request since March, and YIMBY now describes it as dead in committee. White's four March petitions lapsed without a vote after staff opposed three of them on May 21; the November 5 set is his second try.

A statewide override is off the table: voters rejected Question 7, which would have allowed single-family homes on 5,000 sq ft lots, in the November 3 election, and the AP called it November 6 (State primary and election).

What's next

  • Result pending: the November 5 joint Planning Board–Land Use hearing on White's four amendments and the Boynton Yards text amendment (outcome not in our sources yet; Zoning amendments in motion in 2026).
  • Owed to the committee: the solicitor's opinion, the demolition and condo-conversion data and the basement answer. Staff have owed written opinions on the lot-split and inclusionary ideas since May 21. Legistar's record of the October 29 action on 26-1336 is also still missing.
  • Coming: the two accessory-structure amendments on the October 22 Council agenda (sponsor and text not in our sources), and a corrected 26-1336 redline for the Planning Board.
  • After that: Planning Board recommendations, a Land Use vote, then the Council. See the zoning tracker.
  • December 31, 2026: Ewen-Campen leaves the Council for the State House, the deadline he's set for himself (Three Council seats turn over).
  • Pending: the 17 Monmouth St lot split the ZBA heard August 5 (outcome not in our sources yet), and the 146 Jaques St cottage occupancy application. See Before the boards.