ADU Design in Watertown, MA

ADU Design in Massachusetts: what governs your project

Massachusetts' 2024 Affordable Homes Act established ADUs as a by-right use in single-family zoning districts statewide, preempting local bans. Municipalities retain limited ability to impose reasonable regulations on size, setbacks, and design.

Energy code

Approvals are by-right at the local level, but building permits, Title 5 septic compliance, and local health codes still apply. Parking requirements are limited by the state law; fees vary by municipality.

Permitting & plan check

Permitting runs through 351 cities and towns, each with its own building department; Boston's Inspectional Services Department handles the state's largest project volume. Conservation commissions review wetlands impacts separately, and Boston adds its own Article 80 development review for large projects.

Good to know

• Massachusetts has 351 cities and towns, each operating its own building department.
• Boston blue clay is one of the most studied problem soils in American geotechnical engineering.
• The Massachusetts Stretch Energy Code, adopted by most of the state's municipalities, is among the strictest local energy codes in the country.

Every discipline, one team