Chelsea homeowners can now build an accessory dwelling unit, a second small home on a single-family lot, as of right. The council adopted a new section of the zoning ordinance, 34-157, this spring after the Planning Board recommended it in March and the council held its hearing and second reading on April 6. Here is what the ordinance allows and what it does not.
Why now
The city did not choose this. The state’s Affordable Homes Act of 2024 required every community to allow accessory dwelling units by right on single-family lots, with a floor of 900 square feet or half the main house, whichever is smaller, and barred owner-occupancy requirements and parking requirements within half a mile of transit. The City Manager’s January letter to the council said as much: the state “required that all single-family” lots allow them, and the city’s ordinance is written to comply while setting the local rules the state leaves to the municipality.
What the ordinance does
An ADU can be inside the main house, attached to it, or a separate structure in the yard. It needs its own kitchen, bath and entrance. It must meet the dimensional rules of the district, setbacks and height, and the building code. Because most of Chelsea is within half a mile of a bus stop, commuter rail or Silver Line station, the state’s no-parking-requirement rule covers nearly the whole city. The unit may be rented. It may not be condominiumized and sold separately from the main house. Short-term rental of an ADU is governed by the city’s separate short-term rental rules.
The practical limit in Chelsea is the lot. Most of the city’s single-family and two-family houses sit on lots of 3,000 to 5,000 square feet, and a detached backyard unit that meets setbacks will not fit on many of them. The units that get built will mostly be basement and attic conversions and additions.
What to do
The process starts at the Department of Inspectional Services with a building permit application; no special permit or zoning board hearing is needed if the unit meets the ordinance. Homeowners should expect the usual plan review, a separate address for the unit, and an inspection before occupancy. The city has not yet published a plain-language ADU guide of the kind Somerville and Boston put out, and the ordinance text is the only guidance. This article will be updated with the ordinance’s specific size and setback numbers once the adopted text is available rather than the draft.