What's Required in Boston
- Homeowner must reside in the 1-, 2-, or 3-family home on-site.
- Full architectural and structural plans stamped by a MA engineer.
- ADU must contain independent cooking, sleeping, and bathroom facilities.
- Must meet all MA State Building Code (780 CMR) standards.
- Zoning Board of Appeal (ZBA) review may be required for detached units.
- Utility separation or shared capacity must be professionally verified.
How Much Does an ADU Permit Cost in Boston?
Budget $10,000–$22,000 for the Boston permit itself (project-based), issued by the Inspectional Services Department — but treat that as the entry fee, not the total. ADUs are full dwelling units, so the permit stack usually includes building, electrical, plumbing, and mechanical trade permits, plus plan review. One local note: total permit costs include building, electrical, plumbing, and mechanical review. Get an itemized fee estimate from the department before finalizing your budget; the spread between a simple conversion and a new detached build is wide.
ADU Size Limits and Zoning Rules in Boston
Before drawing plans, check the two gates that sink most ADU projects: size and zoning. Size ceilings vary by lot and ADU type (attached, detached, or conversion), so confirm your specific configuration. Other recorded conditions: homeowner must reside in the 1-, 2-, or 3-family home on-site. Setbacks, height limits, and utility connections layer on top of those rules. The Inspectional Services Department can confirm what your specific lot allows — worth doing before you pay for architectural drawings rather than after.
How to Get a ADU Permit in Boston
Step 1: Check Eligibility
Confirm property is a 1-3 family home and you are the resident owner.
Step 2: Design Phase
Hire an architect to create plans meeting ADU Guidebook specs.
Step 3: Portal Submission
Upload all structural and trade drawings to Boston ISD online.
Step 4: ZBA Review
Attend a hearing if a zoning variance is required for your lot.
Step 5: Multi-Stage Inspections
Full series from foundation and framing to final occupancy.