ADU Construction Services in Greater Boston
Boston Deck Builders offers accessory dwelling unit (ADU) construction services for homeowners across Greater Boston. Whether someone needs a guest house, a rental unit, or a private workspace on their property, their team handles ADU projects from planning through completion.
An accessory dwelling unit is a smaller home built on the same lot as a primary residence. These structures go by many names — granny flats, in-law suites, backyard cottages, or casitas — but they all serve the same basic purpose: adding usable living space without requiring a move. ADUs generally fall into one of three categories:
- Detached ADUs — standalone structures in the backyard
- Attached ADUs — garage conversions or additions connected to the main home
- Interior ADUs — basement or attic apartments within the existing structure
Most ADU construction projects take between 6 and 12 months from design through final inspection, depending on the type of unit and how quickly local municipalities process building permits.
There are several practical reasons property owners choose to build an ADU. Common motivations include housing aging parents or adult children nearby, generating rental income, creating a dedicated home office, or simply increasing the overall value of the property.
Modular and Prefab ADU Options
Boston Deck Builders also works with modular and prefab ADU solutions. These units are constructed in a factory setting and then delivered to the property, typically in one or two large sections. Once on-site, the team connects the unit to the foundation and hooks it up to plumbing, electrical, and HVAC systems.
Some advantages of prefab ADUs include:
- Faster build times — factory construction is not affected by weather delays
- Consistent quality — factory environments use repeatable building standards
- Less on-site disruption — reduced noise and construction mess during installation
Modular ADUs are permitted in Massachusetts, but local zoning approval is still required. Some towns have specific rules about the appearance and placement of prefab structures. Site preparation, foundation work, and utility connections are still necessary regardless of the build method. Boston Deck Builders walks clients through the full cost picture — whether they're considering a prefab or a custom-built unit — so there are no unexpected expenses. Prefab models also offer a range of floor plans, sizes, and finish options that can be customized to fit the property and the homeowner's needs.
ADU Regulations in Massachusetts
ADU rules vary by city and town across Greater Boston. The state's Affordable Homes Act, passed in 2021, made it easier to build ADUs by allowing by-right zoning statewide. That said, local requirements still apply and differ from one municipality to the next. Common regulations include:
- Size limits — typically between 900 and 1,200 square feet
- Owner-occupancy requirements in many towns
- Parking space requirements
- Setback and height restrictions
- A limit of one ADU per single-family lot
Cities like Cambridge, Somerville, and Newton tend to have more flexible ADU policies, while suburbs such as Needham, Dedham, and Quincy apply stricter zoning rules. Boston Deck Builders is familiar with local regulations across the region and manages the permitting process accordingly.
The cost to build an ADU in Greater Boston generally ranges from $150,000 to $400,000 or more, depending on size, type, and finish level. Detached ADU builders typically see higher costs than garage conversion contractors or basement conversion projects, largely due to foundation and utility connection requirements.
Boston Deck Builders handles all phases of ADU construction, including site planning, design, permitting, zoning coordination, construction, inspections, and all mechanical finishes. They serve Boston, Cambridge, Newton, Quincy, Brockton, and surrounding communities throughout eastern Massachusetts and the MetroWest region.