The New Massachusetts ADU Law Explained (2025)

How McElhinney Construction Helps You Navigate and Build Your ADU

Building a second unit on your property is now easier than ever in Massachusetts.The new statewide Accessory Dwelling Unit (ADU) law opens the door for homeowners to create rental income, add family space, or increase property value — without the red tape that used to make the process difficult.

At McElhinney Construction, we help homeowners throughout Martha’s Vineyard and Cape Cod design, permit, and build ADUs that meet the new law and fit their property perfectly.

What Changed in 2025

In August 2024, Massachusetts passed a major housing reform known as the Affordable Homes Act, which officially took effect on February 2, 2025.The law allows homeowners to build one Accessory Dwelling Unit by right on most single-family lots across the state.

That means no more lengthy zoning hearings or special permits — as long as your ADU follows a few basic rules.

Key highlights of the new law:

• You may build one ADU on your property as of right.

• The ADU must be no larger than 900 square feet or half the size of your main home, whichever is smaller.

• The unit must have a separate entrance and meet all building and safety codes.

• You are not required to live in either the main home or the ADU.

• Towns may still apply reasonable local regulations, such as setbacks, height limits, or parking requirements, but they cannot ban ADUs outright.

This law was designed to help address housing shortages statewide — and it gives homeowners a powerful new way to unlock value from their property.

Why This Matters for Homeowners

1. FlexibilityAdd space for aging parents, adult children, or guests — or create a rental unit that produces monthly income.

2. Property ValueA well-designed ADU can significantly increase resale value and attract long-term tenants.

3. Simpler PermittingBy-right construction eliminates most of the zoning hurdles that used to delay or block ADU projects.

4. Regional OpportunityOn Martha’s Vineyard and Cape Cod, where housing is tight and land is limited, this new law opens the door for year-round rentals and family housing options that weren’t possible before.

How McElhinney Construction Helps You Build an ADU

Step 1: Feasibility & Site ReviewWe evaluate your property, zoning district, septic or sewer system, utilities, and access points to determine your ADU’s best size and placement.

Step 2: Design & BudgetingOur in-house team and design partners create plans that fit your vision and budget — from modern backyard cottages to above-garage apartments.

Step 3: Permitting & CoordinationWe prepare and submit all required documents, coordinate with your town’s building department, and ensure your ADU fully complies with the new Massachusetts law.

Step 4: ConstructionWe handle everything: excavation, foundation, framing, plumbing, electrical, and high-end finishes. Every build reflects our reputation for craftsmanship and detail.

Step 5: Completion & ValueWe deliver a move-in-ready ADU that adds lasting value to your home, whether you plan to use it for family or rental income.

Questions to Ask Before You Start

• Is my lot eligible under the new ADU law?

• What is the maximum square footage allowed for my property?

• Do I need septic or utility upgrades?

• How much will site work and foundation costs affect my budget?

• What will my rental income or property value increase look like?

Our team helps you answer each of these early, so your project runs smoothly from start to finish.

Plan Your ADU Project Today

If you’re thinking about building an ADU on Martha’s Vineyard or Cape Cod, now is the time to start.The new Massachusetts law has simplified the process — but every property is unique.

Our team can help you understand your town’s requirements, create a design that fits your land, and manage the entire build.

Let’s turn your ADU idea into a fully permitted, beautifully built reality.

Reach out to our team