Boston ADU permit requirements
Last reviewed: June 22, 2026
Quick answer
Permitting an accessory dwelling unit (ADU) in Boston, Massachusetts means pulling a building permit from the local authority that issues it. ArchPermit tracks 15 source-cited requirements (8 required, the rest conditional) for this jurisdiction. Submittals go through ISD Permits & Licenses online portal. These requirements were last reviewed June 22, 2026; confirm the exact forms and fees with the local permitting authority.
A source-cited checklist of what an ADU (accessory dwelling unit) permit package needs in City of Boston. Every item links to its authoritative source; items that vary are flagged to confirm locally.
An ADU requires a long-form building permit (long-form review runs ~4 to 5 weeks if no zoning relief is needed). Boston is governed by its own zoning and is NOT covered by the 2024 Massachusetts Affordable Homes Act statewide by-right ADU provision, which excludes Boston. Today owner-occupants may build an ADU within existing interior space without exterior alterations; full citywide as-of-right ADUs are pending zoning reform (Mattapan is the one neighborhood already amended for by-right, including detached). If the project doesn't conform to zoning, ISD issues a refusal letter and the applicant seeks a variance from the Zoning Board of Appeal within 45 days. Owner-occupancy is required.
- Architectural Construction Documents (existing + proposed)required
Two sets of construction documents: Architectural (existing and proposed) and/or other disciplines, for an ADU up to 2 units.
source · reviewed 2026-06-22 - Construction Cost Estimate with Breakdownrequired
Estimated total construction cost with breakdown (not required for zoning relief).
source · reviewed 2026-06-22 - Copy of Contractor Agreementrequired
A copy of the contractor agreement, a required submittal item.
source · reviewed 2026-06-22 - Licensed Builder Construction Licenserequired
Licensed builder information; only the licensed contractor may apply, and the name must match the license (not required when applying for zoning relief).
source · reviewed 2026-06-22 - Long-Form Building Permit Applicationrequired
All ADUs require a long-form (alteration/new construction) building-permit application, the base filing.
source · reviewed 2026-06-22 - Mattocks-Higgins Affidavit (Workplace Safety)required
Affidavit of workplace safety, listed in the all-applications builder group.
source · reviewed 2026-06-22 - Plans Stamped by a MA Registered Design Professionalrequired
Plans drawn to scale and stamped/signed by a Massachusetts registered design professional (licensed architect).
source · reviewed 2026-06-22 - Workers' Compensation Insurance Affidavitrequired
Workers' compensation affidavit (not required for zoning relief).
source · reviewed 2026-06-22 - Certified Plot Plan (existing + proposed)conditionalverify locally
Two sets by a MA Registered Land Surveyor (three for zoning relief). The ADU checklist row doesn't list it, but long-form new construction/additions require it; confirm per project (e.g. added footprint/parking).
source · reviewed 2026-06-22 - Construction License Exemption for Home Owner(s)conditional
Only for single-family homeowners performing the work themselves without a GC; the homeowner then acts as supervisor.
source · reviewed 2026-06-22 - Fire Sprinkler / Fire Alarm Construction Documentsconditional
Required where a suppression/alarm system is installed (and for ADUs over 2 units): application, narrative, and hydraulic calculations.
source · reviewed 2026-06-22 - Flood Design Affidavit + Elevation Certificateconditional
Required only if the property is in a flood zone.
source · reviewed 2026-06-22 - Home Improvement Contractor (HIC) Registrationconditional
Required for 1 to 4 unit owner-occupied homes (not required for zoning relief).
source · reviewed 2026-06-22 - Stretch Energy Code Compliance Letterconditional
Energy-code compliance documentation, required as applicable.
source · reviewed 2026-06-22 - Zoning Board of Appeal (ZBA) Applicationconditional
Only if the ADU does not conform to zoning. File within 45 days of the refusal letter, with three sets each of certified plot plan, floor plans, and elevations.
source · reviewed 2026-06-22
Boston ADU permit questions
- Do I need a permit to build an ADU in Boston?
- Yes. An accessory dwelling unit (ADU) in Boston requires a building permit. ArchPermit tracks 15 cited requirements for this jurisdiction (8 required, the rest conditional). Always confirm the exact forms, fees, and code edition with the local permitting authority that issues the permit.
- What does an ADU permit package require in Boston?
- Core required items include: Architectural Construction Documents (existing + proposed); Construction Cost Estimate with Breakdown; Copy of Contractor Agreement; Licensed Builder Construction License; Long-Form Building Permit Application; Mattocks-Higgins Affidavit (Workplace Safety), plus 2 more. Each requirement links to its authoritative source, and nothing is permit-ready until an independent licensed professional reviews and seals it.
- How are ADU permits submitted in Boston?
- Boston accepts permit submittals via ISD Permits & Licenses online portal. ArchPermit prepares a draft package you can submit there after a licensed architect reviews and seals it.