Boxford

Massachusetts enacted statewide ADU preemption through the Affordable Homes Act of 2024 — Chapter 150 of the Acts of 2024 — signed by Governor Maura Healey on 2024-08-06. Sections 7 and 8 of the Act amended M.G.L. Chapter 40A (the Zoning Act) Sections 1A and 3, making ADUs a 'protected use' that must be allowed by-right in single-family zoning districts statewide. ADUs are capped at the smaller of 50% of the principal dwelling's gross floor area or 900 square feet. The amendment to Section 3 became effective 2025-02-02 (180 days after the Act's effective date). The implementing regulation, 760 CMR 71.00 (Protected Use Accessory Dwelling Units), was promulgated by the Executive Office of Housing and Livable Communities (EOHLC) and took effect 2025-01-31. Municipalities cannot prohibit ADUs or impose unreasonable regulatory requirements; they retain authority over site-plan review, bulk and height limits, setbacks, and short-term-rental bans. As of 2026-04, more than 1,200 ADUs had been approved statewide in the first year of implementation.

Massachusetts has launched one of the most aggressive ADU-specific state financing programs in the country. MassHousing's Accessory Dwelling Unit Loan Program (ADULP), announced 2026-01-14 by Governor Healey, provides second-mortgage construction financing of up to $250,000 for detached ADUs and up to $150,000 for attached ADUs. The product is structured as a 5.25% fixed-rate, 20-year amortizing loan, with a portion of additional funding offered at 0% interest with deferred repayment terms. Eligible homeowners must meet MassHousing's statutory income limits (up to 135% of Area Median Income — ranging from ~$165K to ~$205K depending on county). MassHousing initially authorized $20M for mission-oriented homeownership, with a portion supporting ADULP. The Massachusetts Housing Partnership administers a separate $10M ADU Technical Assistance Program for predevelopment activities. The Massachusetts Housing Partnership's One Mortgage program also includes an ADU Incentive Program component.

• MassHousing Accessory Dwelling Unit Loan Program (ADULP)
• Massachusetts Housing Partnership ADU Incentive Program
• Massachusetts Housing Partnership ADU Technical Assistance Program

Massachusetts operates an integrated state-level ADU program suite combining preemption (760 CMR 71.00 + M.G.L. c. 40A), construction financing (MassHousing ADULP), technical assistance (MHP $10M program), and a no-cost ADU Design Challenge launching replicable plan templates. Governor Healey announced this campaign in 2026 alongside the 1,200+ ADU first-year approval milestone. The state does not yet operate a statewide impact-fee waiver, but municipalities cannot impose unreasonable regulatory requirements per the Act.

• Affordable Homes Act ADU Protected-Use Framework (760 CMR 71.00) — ADUs by-right in single-family districts statewide, capped at smaller of 50% of principal dwelling or 900 sqft. Implementing regulation defines model bylaw provisions and municipal-compliance requirements.
• MassHousing ADU Loan Program (ADULP) — 5.25% fixed-rate second mortgage up to $250K (detached) or $150K (attached), 20-year amortization, with a portion at 0% deferred. Launched 2026-01-14.
• MHP ADU Technical Assistance Program — $10M state-funded program administered by Massachusetts Housing Partnership for ADU predevelopment — site evaluation, design, permit preparation, contractor coordination.
• ADU Design Challenge — Healey administration program launching replicable, no-cost ADU design templates for use across Massachusetts municipalities.