The Affordable Homes Act legalized ADUs by-right in every zoning district subject to the Zoning Enabling Act (this excludes the City of Boston.) As authorized, EOHLC promulgated regulations to implement the law. After a public comment period, the regulations went into effect on February 2, 2025. Protected Use ADUs of less than 900 square feet or half the size of the primary dwelling, whichever is greater, are permitted in every single-family zone and may not be subject to owner-occupancy restrictions. If a property owner seeks to create a unit that qualifies as a “Protected Use ADU”, they may take their plans directly to the local building inspector for a building permit. Municipalities may adopt reasonable regulations governing ADUs, with administrative approval. This law will open up opportunities for thousands of homeowners across the state to create separate small units.
Early reports from building inspectors indicate that the high cost of construction remains a major barrier to ADU adoption. The cost of labor and materials, building code requirements that mandate complete fire separation, and necessary upgrades to septic systems can drive the total cost of an ADU to $500,000, according to some inspectors EOHLC surveyed. Access to capital for homeowners is a known challenge, especially for low-income homeowners and those on a fixed income. Local interpretation of fire codes may require additional protective measures (possibly including sprinklers) for detached ADUs that cannot be reached by a fire lane. Managing the design and construction process is a complicated endeavor. Some property owners may have trouble finding qualified contractors and would benefit from a ‘turnkey’ solution, especially detached ADUs. Data collection requirements in the ADU regulations will provide a better window into the uptake, cost, and location of new ADUs, and may help identify additional areas of policy changes.