Cost of accessory dwelling unit — Boston, MA | AccessoryDwellingUnit Services

Looking for cost of accessory dwelling unit in Boston, MA? Call AccessoryDwellingUnit Services for a contact a provider — no obligation. Licensed adu builders serve Boston and the surrounding area, and you'll get straight answers on timing and what affects the price.

Last updated: September 24, 2026

What affects the price

Building an ADU involves several moving parts that shape your total investment. The final figure depends heavily on whether you choose a prefab unit or a custom build from the ground up. Site conditions are another major factor; if your property requires extensive grading, utility trenching, or foundation work, costs will climb. You also have to consider your choice of finishes, like high-end appliances or custom cabinetry. Navigating local permit fees and impact assessments also adds to the total.

About this service

Building an ADU involves several variables that shift the total investment. Your site conditions, the type of foundation, and the quality of finishes you choose will dictate whether you land on the lower or higher end of the spectrum. Because every lot is unique, we provide a breakdown of your specific project requirements to ensure full transparency. Exact pricing confirmed free on the call.

Frequently asked in Boston

What are the disadvantages of ADUs?

Building an ADU in Boston requires significant upfront planning and time to navigate local permitting. You may face construction noise that impacts your daily routine in dense areas like Dorchester or Roxbury. Additionally, property taxes might increase after your project is assessed. Call us to discuss if these factors outweigh the benefits for your home.

How much does an ADU cost in Massachusetts?

What are the rules for ADUs in California?

While you are asking about California rules, please note that Boston operates under its own municipal zoning ordinances for accessory dwellings. Massachusetts laws differ significantly from West Coast regulations regarding unit size and parking requirements. Our local pros understand exactly what the City of Boston allows. Call us today to learn about local requirements.

Is ADU allowed in Maryland?

You are inquiring about Maryland regulations, but our service focus is on the Boston area. Massachusetts has its own specific set of rules for secondary units that differ from Baltimore or other Maryland cities. We specialize in helping Boston homeowners understand local zoning. Call now for advice on what is permitted on your lot.

What are the rules for ADU in California?

Regulations for accessory units in California do not apply to your property in Boston. Massachusetts properties are subject to local zoning ordinances that dictate height, footprint, and occupancy limits. The specialist you speak with can provide accurate information regarding current Boston codes. Call us now to get the right answers for your project.

Also serving nearby: Quincy · Cambridge · Lynn · Newton · Brockton

All cities in Massachusetts →

More on this: HUD ADU resources — ADU policy and financing research.

Service area details

653,833residents

13,525per sq mile

8ZIP codes served

Serving all of Boston — population 653,833; about 13,525 residents per square mile across 48.3 sq mi. ZIP codes covered include 02108, 02109, 02110, 02111, 02112, 02113, 02114, 02115.

Neighborhoods served in Boston: Beacon Hill, South Boston, Dorchester, Roxbury, Back Bay — and every surrounding area.