What Is an ADU and Why Are Massachusetts Homeowners Building Them?
An Accessory Dwelling Unit (ADU) is a self-contained secondary living space located on the same property as a primary residence. It can take several forms — a detached backyard cottage, an attached in-law suite, or an interior conversion such as a finished basement with a separate entrance. These units typically include a kitchen, bathroom, and private entrance, making them fully independent living spaces.
Homeowners across Massachusetts are increasingly turning to ADUs for a range of practical reasons:
- Housing for aging parents or adult children
- Generating rental income
- Providing space for a live-in caregiver
- Creating a private home office or guest space
As of August 2024, Massachusetts passed statewide legislation making ADUs legal by right in every municipality. This means most previous zoning hurdles — such as owner-occupancy requirements or discretionary approvals — have been removed. Under the new law, ADUs can be up to 900 square feet, or half the size of the primary home, whichever is smaller.
That said, local factors such as building height caps, drainage requirements, setback rules, and design restrictions can still vary by town. Working with a knowledgeable local ADU contractor remains an important part of navigating the process successfully.
MBA Builders: A Structured Approach to ADU Construction
MBA Builders is a Massachusetts-based construction company that works with homeowners on ADU projects, from initial planning through to completed construction. They operate across the Greater Boston area and have developed a defined process specifically aimed at managing the complexity that comes with high-investment home projects like accessory dwelling unit builds.
Their approach is divided into two main phases:
- Preconstruction Planning — This phase begins with an initial consultation to assess whether an ADU is a realistic fit for the homeowner's goals and property. MBA Builders' design team visits the site, reviews local zoning requirements, and develops a Preconstruction Agreement. This covers site assessments, architectural plans, finish selections, detailed specifications, and budget forecasting.
- The Build — Once plans are approved and finalized, the construction team takes over. Work covers everything from utilities and framing to interior finishes, all executed according to the plans developed during preconstruction.
By investing in thorough planning before construction begins, MBA Builders aims to deliver construction estimates that are typically within 10% accuracy — a meaningful distinction compared to contractors who move straight into building without detailed upfront planning.
Their team includes client care coordinators, design consultants, project managers, and tradespeople, providing a full-service structure throughout the project.
Navigating ADU Costs and Permitting in Massachusetts
The cost of building an ADU in Massachusetts depends on several variables, including the size of the unit, chosen finishes, and site-specific conditions. For a detached ADU built from the ground up — including a new foundation and utility connections — pricing typically starts around $450 per square foot. Architectural plans and detailed specifications are priced separately as part of the preconstruction phase.
Factors that can influence the final cost include:
- Distance from the main house or existing utility sources
- Site grading challenges, such as ledge or drainage issues
- Demolition of existing structures
On the permitting side, while the 2024 state legislation has streamlined zoning approvals significantly, individual towns are still interpreting and applying the new rules in different ways. Some municipalities have introduced design guidelines or site preparation requirements that can add time or cost to a project. MBA Builders' familiarity with Greater Boston municipalities means they can identify potential complications early — before a homeowner commits to a project.
For homeowners considering a garage conversion, granny flat, casita, or fully detached ADU builder project, MBA Builders offers a structured path from feasibility assessment through to a finished, permitted unit.