Planning an ADU in Massachusetts: What Homeowners Should Know
Accessory Dwelling Units (ADUs) are becoming an increasingly popular option for homeowners in Massachusetts looking to expand their living space, accommodate multigenerational families, or generate rental income. With recent changes in state regulations and growing interest in compact, functional living, many property owners are exploring whether an ADU makes sense for their situation.
Sordan Construction is a full-service ADU contractor serving the Greater Boston area. They work with homeowners on a range of ADU projects, from backyard cottage builds to basement conversions, offering design and construction services under one roof.
Average Cost to Build an ADU in Massachusetts
Building an accessory dwelling unit in Massachusetts varies significantly based on design, site conditions, and finishes. Current data points to the following general ranges:
- Standard Construction: $250–$325 per square foot
- High-Performance Builds: $350–$500+ per square foot
For a 900 sq ft ADU, homeowners can typically expect to pay between $250,000 and $450,000. This estimate generally includes structural work, plumbing, electrical, and finished materials. Costs will vary depending on the specific scope of the project and local conditions.
Permitting and Code Considerations
Massachusetts passed a law in 2023, effective February 2024, requiring all cities and towns to allow at least one ADU by right on single-family lots. However, individual municipalities may still apply their own rules and processes on top of state requirements.
For homeowners in the City of Boston, the following steps are typically involved:
- Submit plans to the Boston Inspectional Services Department (ISD)
- Obtain additional permits as needed — plumbing, electrical, HVAC, or fire protection
- Review zoning and design guidelines, which can vary by neighborhood
As of February 14, 2025, Massachusetts also adopted 225 CMR 22.0, a set of energy-efficiency standards known as the Stretch Energy Code. This applies to low-rise residential properties and is an important consideration for any new ADU construction in the state.
Navigating these layers of regulation is one reason many homeowners choose to work with an experienced ADU builder rather than managing the process independently.
Working with a qualified ADU contractor like Sordan Construction can help address several key challenges:
- Code Compliance: Staying current with local and state building codes to keep the project on the right side of regulations
- Permit Management: Handling applications, inspections, and coordination with city departments
- Design-Build Expertise: Making efficient use of space without exceeding budget
- End-to-End Service: Managing the project from initial concept through to completion
Sordan Construction focuses on ADU design and construction across Greater Boston. Whether the goal is a detached ADU in the backyard, an in-law suite, or a basement conversion, they work with homeowners to develop solutions suited to their property and objectives.