Massachusetts ADU Law Explained: The Affordable Homes Act (2025 Update)

Massachusetts changed the game. With the Affordable Homes Act, ADUs (Accessory Dwelling Units) are now allowed by-right across single-family lots that meet the standards. In this realtor-focused briefing, Paul Crossman of BuildX breaks down exactly how the law works in practice—so you can guide sellers, buyers, and investors with confidence. What you’ll learn: • By-Right ADUs: where they’re allowed and how the process works • Size limits: the smaller of 900 sq ft or 50% of the existing home’s gross floor area • How gross floor area is measured from the inside of the walls • Counting unfinished attic or basement space with at least 6’8” headroom • Why a crawlspace can avoid counting as livable area • Attached vs detached ADUs and required separate entrances • Parking rules: zero spaces within ½ mile of public transit, one space otherwise • Title 5 compliance: sewer, septic, and private well requirements • Setback and zoning rules that still apply under the new law • Rental regulations: no short-term rentals, 30-day minimum stays • Realistic cost ranges for small and large ADUs • Pros and cons of modular vs traditional builds • Converting basements, attics, and garages into ADUs • Why involving a builder early saves time, cost, and headaches Equip your clients with clear answers—and win more listings by positioning ADUs as a strategic option for multi-generational living, aging-in-place, and long-term value. ⏱️ Chapters 00:00 – Welcome & Purpose: Why ADUs matter to Realtors 00:18 – What is an ADU? Legal definition & “small house” reality 00:44 – Why the Affordable Homes Act was passed (more housing on existing lots) 01:22 – By-Right Overview: Single-family, ownership, no STRs, separate entrance 02:05 – Size Limits: 900 sq ft or 50% of GFA (measured inside the walls) 02:44 – Counting Space: Attic/cellar ≥ 6’8” count; crawlspace strategy 03:34 – Attached vs. Detached & Entrance requirements (building code) 04:05 – Setbacks & Site Constraints: What didn’t change 04:33 – Title 5, Sewer, & Private Wells: How capacity and rules work 05:34 – Parking Rules: Transit half-mile = 0 spaces; otherwise one space 06:05 – Cost Ranges by Size: Small (≈550–750) vs. large (≈750–900) 06:49 – Modular vs. Stick-Built: Cost/time myths & material control 07:18 – Tiny Homes & Minimums; when they qualify as ADUs 07:43 – Addition vs. ADU: Permitting advantages & use-case logic 08:14 – Conversions: Basement/attic/garage viability & egress 08:43 – Town-by-Town Nuances: Patience and process 09:13 – Why Realtors Should Loop in a Builder Early 09:45 – Resources on BuildX.com for lenders, engineers, permitting #BuildX #BuzArtiano #ADU #Massachusetts #AffordableHomesAct #Realtor #RealEstate #Title5 #Zoning #Housing #ByRight #Permitting #JustBuildBaby #Carver #Plymouth Help your clients unlock ADU value—without surprises. 🌐 Explore ADU playbooks, plans, and permitting guides: BuildX.com 📺 Watch more trainings and case studies: @BuildX_USA 📩 Get monthly ADU updates for Massachusetts Realtors. Just Build Baby! 🇺🇸