Your Complete Guide to Building an ADU in Massachusetts: Space, Income, and MA ADU Rules
Need more room at home or a reliable way to bring in extra income—without the stress of selling or moving? A Massachusetts ADU (Accessory Dwelling Unit) might be exactly what you need. Whether you're converting a basement into a cozy rental or building a new backyard cottage for extended family, ADUs can be a smart and flexible way to unlock the full potential of your property.
Thanks to recent updates to state law, adding a MA ADU is more accessible than ever—especially when you’re working with a trusted and experienced MA ADU contractor like us at FiveTen Construction & Design!
What is an ADU?
An Accessory Dwelling Unit (ADU) is a smaller, independent living unit located on the same lot as a single-family home. It’s a fully functional mini-home with a kitchen, bathroom, and living space, all under one roof. ADUs are a great solution for adding space, generating rental income, or offering a private spot for family—all without needing to move or buy a second property.
Types of ADUs in Massachusetts
ADU Basement Conversion – A popular, cost-effective option where a qualified Massachusetts ADU contractor transforms your existing basement into a livable unit.
Attached ADU
A new addition built onto your main home.
Above garage unit
Interior upper level addition
Garage conversion
Detached ADU – A separate structure like a backyard cottage, guest house, or converted garage.
No matter the style, a skilled MA ADU contractor like FiveTen Construction & Design can help you choose the best fit for your property and goals.
Key Rules for ADUs in Massachusetts
If you’re planning to build a Massachusetts ADU, here are the major rules to know:
Size Limit: The ADU must be 900 sq. ft. or smaller, or up to 50% of your main home’s floor area—whichever is less.
Zoning: ADUs are allowed by-right in single-family zones. For multifamily properties (like duplexes), local zoning laws apply.
Owner-Occupancy: You’re not required to live on the property.
Parking: An additional off-street parking space is generally required. However, if you're within ½ mile of a transit station, you can’t be required to add parking just for the ADU.
Utilities: Separate utility are not be required.
MA ADU Building Code Checklist
Planning an ADU basement conversion or new unit? As your Massachusetts ADU contractor we will make sure your unit meets all state and local building codes, including:
1-hour fire separation between units
Proper ventilation and natural light
Minimum room size (70 sq. ft.) and ceiling height (7 ft.)
Two safe exit routes (means of egress)
Interconnected smoke and carbon monoxide detectors
Compliance with Massachusetts’ stretch energy code
Legal Uses for ADUs in MA
ADUs are designed for long-term, sustainable housing—not for short-term rental turnover. Here’s what’s allowed (and what’s not):
✓ You Can Use Your ADU For:
Long-term rentals to generate steady income
Multi-generational living (aging parents, adult kids, caregivers)
A home office, studio, or private guest space
✗ You Can’t Use It For:
Short-term rentals (like Airbnb) unless your city or town specifically allows it
Selling the ADU separately from the main home
The Bottom Line
ADUs are more than just extra space—they’re a smart way to build value, support family, and invest in your future. Whether you’re looking to convert your basement, build in your backyard, or just learn the basics, feel free to save and reference our ADU Reference Guide is your first step toward making it happen.
Ready to start your Massachusetts ADU project? Connect with us, a reliable MA ADU contractor to explore your options and get it done right.
Why Choose FiveTen Construction & Design as your Trusted ADU Contractor?
Building an ADU in Massachusetts isn’t just another home renovation—it’s the creation of a fully legal residential unit. This means navigating complex permits, zoning reviews, and building code inspections. Working with an experienced Massachusetts ADU contractor like FiveTen Construction & Design ensures that every step, from initial design to final inspection, is handled expertly and efficiently.
Whether you're building a detached unit, an attached addition, or planning an ADU basement conversion, we’ll help you avoid costly delays, stay on budget, and maximize your space. Basement ADUs, in particular, come with unique structural challenges and strict code requirements under current MA ADU rules—and we have the expertise to guide you through it all.
As a trusted MA ADU contractor, our goal is to make your project smooth, successful, and even exciting. Here’s exactly what you can expect when you partner with us:Personalized Consultation:
We begin by learning about your vision, needs, and goals. Whether you're planning a detached ADU, converting an existing garage, or adding to your home, we'll guide you through all your options while keeping Massachusetts ADU rules in mind. Here’s what you can expect when you work with us:
Customized ADU Design:
If you're considering a basement ADU, our team will help you design smart layouts and create detailed renderings so you can visualize your space before construction begins. This process ensures all options and details are reviewed up front, with no surprises later.
For larger projects like attached or detached ADUs, we’ll walk you through every step—reviewing architectural plans, helping you plan for every detail, and making sure your ADU maximizes space, light, and functionality. As an experienced MA ADU contractor, we ensure your new space looks amazing and meets all your goals.
Transparent Budgeting:
Understanding the cost of your ADU is key. We provide clear, detailed estimates and work with you to select finishes that match your style and stay within budget. Our project management system keeps you fully informed and in control throughout the process.
Expert Navigation of MA ADU Rules and Permitting:
Permitting for ADUs in Massachusetts can be complex. Our team handles the permitting process for you, ensuring full compliance with all MA ADU rules and local zoning laws in Middlesex and Essex counties. You can trust us to get your project approved efficiently and correctly.
High-Quality Construction:
As a leading Massachusetts ADU contractor, we pride ourselves on top-tier craftsmanship. From the foundation to the final finishes, your ADU will be built to the highest standards with lasting quality in mind.
Final Walkthrough and Handover:
When construction wraps up, we’ll walk you through your brand-new ADU, ensuring every detail is exactly what you envisioned. Your complete satisfaction is our #1 priority.
