Cost of accessory dwelling unit — Boston, MA

Looking for cost of accessory dwelling unit in Boston, MA? Call AccessoryDwellingUnit Pros 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 is a custom project, so costs vary based on your specific choices. Site conditions are the biggest factor; if your land requires significant grading, utility extensions, or foundation work, those expenses add up quickly. Choosing high-end finishes, custom cabinetry, or complex roof lines will also push the budget higher compared to a standard design. Prefabricated units often offer predictable costs, while custom site-built structures allow for more flexibility but can be harder to estimate upfront. Exact pricing confirmed free on the call.

About this service

The total investment for an ADU depends on several moving parts, including your property’s site conditions, the complexity of your site plan, and the high-end finishes you select. Whether you are building a detached cottage or converting a garage, costs vary based on utility connections and local labor rates. Exact pricing confirmed free on the call.

Frequently asked in Boston

What are the disadvantages of ADUs in Boston?

In Boston, potential disadvantages include navigating complex city zoning regulations and the initial construction costs. You'll also need to consider how an ADU might impact your property's yard space or existing utilities. It's important to consult with local experts to understand all potential drawbacks for your specific location.

How much does an ADU cost in Massachusetts?

What are the rules for ADUs in California?

California has state-level laws that streamline ADU development, but local ordinances still apply. These rules often cover setbacks, height limits, and parking requirements. Cities like Los Angeles and San Francisco have specific guidelines to follow, so checking with the local planning department is crucial.

Is ADU allowed in Maryland?

Yes, ADUs are permitted in many areas of Maryland, with specific regulations varying by county and municipality. Baltimore County and Montgomery County, for example, have different rules regarding size, placement, and owner occupancy. It's essential to check your local zoning laws.

What are the rules for ADU in California?

California's ADU laws aim to simplify building accessory dwelling units. Key state provisions often dictate maximum unit size, minimum setbacks, and owner-occupancy requirements. However, individual cities can impose some local standards, so verifying with your city's planning department is always recommended.

California has offered various grant programs to help homeowners with the cost of building ADUs. These programs often have specific eligibility requirements and funding limits. The availability and terms of such grants can change, so it's wise to research current state and local initiatives.

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: Back Bay, Beacon Hill, South End, Jamaica Plain, Dorchester, North End — and every surrounding area.