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Planning staff outlines ADU rules and options as state law expands accessory units; board to consider local design standards
Summary
Planning staff briefed the board on state ADU rules, what the city can and cannot regulate, and possible local options such as open-space flexibility, design guidelines in historic districts and tax/incentive approaches to encourage long-term affordable ADU rentals.
City planning staff presented an informational briefing on accessory dwelling units (ADUs) and options the city could pursue to implement a local ADU ordinance that aligns with Massachusetts law.
Staff reviewed the state framework: a protected-use ADU is a by-right use in single-family zoning districts if it is no larger than 900 square feet or half the gross floor area of the primary residence (whichever is smaller) and has a separate entrance. Staff noted state law limits what localities can require: municipalities may not impose owner‑occupancy, familial, income or age restrictions; they may not count ADUs toward unit caps or density limits and may not add parking requirements for ADUs in areas within a half-mile of transit (Chelsea largely falls inside that radius).
Staff said what cities can require or adopt locally includes dimensional standards consistent with the primary dwelling, objective and measurable design guidelines in historic districts, bans on basement ADUs in mapped flood hazards, and restrictions on short-term rentals of ADUs. Staff floated possible local measures to encourage desirable outcomes: easing the 10x10 open-space counting rule (for example to 5x5) to facilitate detached ADUs or small additions, requiring permeable surface standards to guard against front-yard paving, and pursuing assessor-based tax incentives if ADUs are rented below-market (Salem’s model was cited as an example).
Board members asked practical questions about enforcement, how gross floor area is tallied, floodplain restrictions and building‑code review; staff said Inspectional Services and assessors will have roles in code enforcement and valuation. Board members asked staff to draft potential objective design guidelines for historic-district contexts and to return with assessors’ input on tax/incentive options.
Staff said about a dozen residents have already sought denial/allowance letters from Inspectional Services and that most likely short-term demand in Chelsea will be for interior ADUs (basement and attic conversions). The board requested staff return with draft ordinance language and examples ahead of a formal zoning proposal.
