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 ~4–5 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.
- Construction Cost Estimate with Breakdownrequired
Estimated total construction cost with breakdown (not required for zoning relief).
source · reviewed 2026-06-22 - Construction Documents — Architectural (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 - 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 1–4 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