Southborough planners weigh changes to ADU bylaw to align with state rules

The Zoning Board of Appeals presented proposed edits to Southborough's accessory dwelling unit (ADU) bylaw on Feb. 9, urging the Planning Board to reconcile local language with the statelawthat guarantees a 900-square-foot by-right ADU. Doris Cahill, a ZBA member, said the local rule tying ADU size to "no larger than half the gross floor area of the principal dwelling unit" "seemed unfair" to owners of smaller homes and urged the town to remove or replace that percentage test.

Planning board members and residents discussed several options to address the fairness concern. Supporters said keeping the state-mandated 900-square-foot floor area as a baseline while removing the percentage test would give smaller-homeowners access to usable ADUs; others proposed a clear cap (board discussion raised figures including 1,200 square feet) or a straightforward rule that an ADU not exceed the primary dwelling. Several board members emphasized simplicity: "simpler is better," one member said, arguing that straightforward numeric caps reduce room for disputes and special-permit workarounds.

Speakers also flagged implementation issues. The board discussed whether converting garages should remain subject to special permits, how historic-adaptive-reuse incentives would be affected if percentage rules were removed, and whether the special-permit criteria should include clearer standards so applicants know discretionary thresholds in advance. A member warned of unintended consequences of removing guidance without new dimensional or design safeguards.

Next steps: staff and the ZBA agreed to circulate a redlined draft reflecting the day's discussion. The Planning Board indicated it aims to advertise a public hearing and, if drafts and legal review are complete, open that hearing on March 9.