ADU law comparison, New Hampshire vs. Massachusetts vs. Maine: all three guarantee accessory dwelling units by right. New Hampshire allows attached or detached ADUs up to 950 sq ft (July 2025); towns may require owner occupancy of either unit. Massachusetts allows one ADU per lot up to 900 sq ft or 50% of home size, whichever is smaller (Feb 2025), and bans owner-occupancy rules statewide (Boston excluded). Maine sets a 190 sq ft minimum floor with no owner-occupancy requirement (July 2024), the earliest of the three laws