Ayer, MA Accessory Structures: Shed Rules (2026)

Middlesex County has no functioning executive government. Chapter 48 of the Acts of 1997 abolished the county on July 11, 1997, transferring its functions to the Commonwealth and leaving only the Sheriff and Registers of Deeds as elected officials. There is no county zoning office, no county building inspector, and no county-level shed ordinance. The applicable statewide framework is 780 CMR (Massachusetts State Building Code, currently 10th edition based on the IRC). Under 780 CMR R105.2, item 1, a one-story detached accessory structure used as a tool or storage shed, playhouse, or similar use is exempt from a building permit if the floor area does not exceed 200 square feet. Above 200 square feet, a building permit from the local town building department is required. Even when no building permit is needed, the shed must comply with the local zoning bylaw of the city or town where the property sits, including setbacks from lot lines, lot coverage, and accessory-structure size limits, which vary widely (commonly 5-10 ft side/rear setback in Middlesex towns). Many Middlesex towns (Cambridge, Newton, Lexington, Concord, Arlington, Belmont, Sudbury, Wayland) require a separate zoning permit or accessory-structure registration even for sheds under 200 sq ft. Confirm local setbacks with the building department of the specific town before installation.