Boston ADU Permitting FAQ

1. Confirm your property is eligible under the statewide by-right law.
2. Prepare plans with a licensed architect or designer.
3. Submit to Boston Inspectional Services Department (ISD) via the online portal.
4. Receive zoning review (30–60 days for standard projects).
5. Historic Commission review if applicable (adds 3–6 months).
6. Obtain building permit and start construction.
7. Schedule final inspections and receive Certificate of Occupancy.

• Maximum size: 900 sq ft or 50% of the principal dwelling (whichever is smaller).
• Allowed in most residential districts by-right.
• No owner-occupancy requirement for the primary home.
• Off-street parking is not required if within ½ mile of transit.
• Must meet all setback, height, and lot coverage rules of the underlying zoning district.

• Front setback: Same as the principal dwelling (typically 10–20 ft).
• Side setback: Minimum 5 ft (3 ft for attached ADUs).
• Rear setback: Minimum 10 ft (reduced in some districts).
• Historic districts or special overlay zones may require greater setbacks or design review.

• Separate electric, gas (if applicable), and water meters are strongly recommended.
• Must comply with current energy code (2023 or newer).
• Sewer connection typically requires a separate line or approved shared system.
• Fire separation and egress requirements apply for attached units.

• Standard non-historic project: 30–60 days from submission to permit.
• Projects in historic districts: 3–9+ months due to Commission review.
• Full process (design through permit): 4–8 months typical for most homeowners.
• Construction phase: 6–12 months depending on size and complexity.

Yes — Boston requires a separate, independent entrance for all ADUs. It must be clearly visible from the street or a common path and meet accessibility standards where required.

Yes, but it requires additional review by the Boston Landmarks Commission or local historic district commission. Expect 3–6 months of extra time and potential design modifications to match the historic character.