Cost to build accessory dwelling unit

Looking for cost to build 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

Determining the cost requires looking at site preparation, foundation work, and the level of interior finishing you choose. Costs change based on whether you opt for a pre-designed layout or custom architecture. You should research these costs when you are ready to evaluate the financial return of your property upgrade. Exact pricing confirmed free on the call.

Frequently asked in Boston

What are the disadvantages of ADUs in Boston?

How much does an ADU cost in Massachusetts?

What are the rules for ADUs in California?

California has state-level ADU laws that streamline approvals, but local cities can have their own specific requirements. These often cover lot coverage, setbacks, and parking. It's essential to check with the local building department. We can help you find specialists familiar with these regulations.

Is an ADU allowed in Maryland?

What are the rules for ADU in California?

California has offered grants to help homeowners build ADUs, often aimed at making them more affordable for low-income households. These programs have specific eligibility requirements and application processes. The pros can help you explore potential funding options if available in your area.

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

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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, North End, Dorchester — and every surrounding area.