ADUs IN MA

What is an Accessory Dwelling Unit (ADU)?

An Accessory Dwelling Unit (ADU) is a self-contained residential living space that is located on the same lot as a primary home. It may be created in a variety of ways:

Converting part of the existing home (for example a basement, attic, or garage)
Adding on to the existing home (an attached unit)
Building a separate “cottage” or detached structure in the backyard

An ADU typically contains its own entrance, kitchen, bathroom, and living space, making it fully independent while still being located on the same property. It can serve different purposes: providing housing for an aging parent or adult child, generating rental income, creating a turnkey guest suite, or adding flexible living space that increases property value.

When you’re planning an ADU, materials and building supplies matter—from insulation to windows, plumbing, heating/cooling systems, and finishes—so aligning with a trusted supplier of “ADU-ready” building supplies can help ensure durability, code compliance and efficiency. (For instance, some local suppliers and lumberyards in Massachusetts now publish guides for ADU projects and help homeowners with materials that meet the new state regulations.)

In short: an ADU gives homeowners more flexibility — more living options on their property — while making efficient use of land, utilities and infrastructure.

ADU Law in Massachusetts – What’s Changed

In Massachusetts, major changes took effect recently that make building ADUs significantly easier across the commonwealth.

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Here are the key points:

Legal Foundation

The law known as the Affordable Homes Act (signed by Governor Maura Healey in August 2024) included provisions to allow ADUs statewide. The Arc of Massachusetts+3Adler Pollock & Sheehan P.C.+3Massachusetts Government+3
The implementing regulations – the “Protected Use ADU” regulations, also known as 760 CMR 71.00 — took effect January 31 2025 and became enforceable as of February 2 2025. Massachusetts Government+2Massachusetts Government+2

What Homeowners Now Can Do

In most single-family zoning districts, an ADU can be built by-right (i.e., without requiring a special permit or zoning variance) as long as it meets the state’s criteria. Massachusetts Government+1
Size limits: The ADU may be no larger than 900 square feet or ½ the gross floor area of the principal dwelling, whichever is smaller. McGregor Law+2Massachusetts Government+2
Municipalities cannot require unreasonable restrictions on the creation or rental of an ADU (that is not a short-term rental) and cannot impose standard rules that are more restrictive than what the state allows. Massachusetts Government+1
Local rules may still apply (setbacks, lot coverage, septic or Title 5 issues, building code) but any zoning by-law conflicting with the state law is unenforceable after the effective date. Massachusetts Government+1

Why This Matters

It opens up many more properties across Massachusetts where ADUs are now feasible, providing more housing flexibility. CBS News+1
For homeowners, it offers opportunities: for example multigenerational living, rental income, increased property value, and more efficient use of land. 02038

What To Watch For / Practical Considerations

You still need to comply with building and health/safety codes (building permit, egress, utilities, septic or sewer issues). The law does not exempt ADUs from these requirements. Massachusetts Government+1
Even though many permitting barriers are reduced, local municipal zoning and planning departments are still working to update their bylaws and systems. So checking with your local city/town is key. Town of Nahant, MA+1
While the state sets the minimum rights, towns may allow more permissive standards (for example larger ADUs or more flexibility) but they cannot impose overly restrictive rules for state-protected “Protected Use ADUs”. Massachusetts Government

Why This Matters for [Your Business / Visitors]

Since the supply chain for building an ADU involves many materials (framing, insulation, flooring, HVAC, plumbing, windows, finishes), having the right building supplies vendor is important. As homeowners and contractors rush to take advantage of the new law, ensuring high-quality, code-compliant materials helps avoid delays, cost overruns or compliance issues.

If you’re a homeowner in Massachusetts considering building an ADU — or a contractor working with ADU clients — now is a great time to:

Evaluate your lot and zoning: confirm that your property is in a district that allows single-family housing (by-right or special permit) and check local ADU-friendly bylaws.
Plan your ADU size and type: decide whether internal (basement/garage conversion), attached, or detached unit makes sense — keeping the size limit (900 sq ft or ½ the house) in mind.
Select your building materials & supplies early: since timelines are shortening with the simplified ADU permitting, locking in trade partners and supply sources (especially for specialty items) helps.
Work with design/permit professionals: even though zoning hurdles are reduced, you still need to permit the build and meet structural, plumbing, code, septic/sewer requirements.
Budget accordingly: while ADUs may cost less than a full new home, you’re still building a fully functional dwelling unit — so factor in finishes, materials, utilities and inspections.

Explore Real ADU Projects in Our Portfolio

Curious about what your own Accessory Dwelling Unit could look like? Visit our Portfolio page to see completed ADUs across Massachusetts. Each project showcases our attention to detail, thoughtful layouts, and high-quality craftsmanship that help homeowners create independent living spaces designed for comfort and value.