Boston

1. Confirm zoning district and ADU pathway via Boston Zoning Viewer (~5d)
   Use the Boston Zoning Viewer (zoningviewer.boston.gov) to identify the parcel's Article (e.g., Article 51 South Boston, Article 60 Mattapan, Article 65 Dorchester). Mattapan parcels under Article 60 Table D may have by-right detached ADU approval; all other neighborhood articles still require ZBA conditional use under Article 6 / Article 8 procedures because Boston's St. 1956 c.665 zoning carve-out preserves discretionary review even after the Affordable Homes Act.
2. Attend BPDA / Mayor's Office of Housing ADU Design Workshop (~30d)
   Free workshop held first Wednesday/Thursday of each month, 4:00-5:30 PM virtual. Boston Planning Department and Mayor's Office of Housing staff (Will Cohen, Senior Zoning Reform Planner II, and Boston Home Center) review preliminary plans before formal submission. Strongly recommended given Boston's narrow lot widths (median ~25 ft frontage in three-decker neighborhoods) and dense parcel patterns. The companion ADU Budget Workshop covers Boston-specific construction-cost realities.
3. ZBA application (if not in Mattapan as-of-right area) (~90d)
   File ZBA application at City Hall for conditional use variance. Required even for ADUs that meet state Affordable Homes Act dimensional caps because Boston's home-rule zoning has not yet adopted the citywide as-of-right rule. ZBA appeal fee is $150 flat. Hearing scheduled within ~45 days of filing; abutter notification per Article 6 procedures. ZBA approval letter must be recorded at Suffolk Registry of Deeds before ISD permit issuance.
4. Submit Long-Form Building Permit via permitfinder.boston.gov (~35d)
   All ADUs require a long-form permit (not the short-form which only applies to interior-only minor work). File online at permitfinder.boston.gov or in-person at ISD's office at 1010 Massachusetts Avenue, 5th Floor. Required exhibits: stamped architect/engineer plans (Boston requires MA-licensed RA stamp), site plan with abutter dimensions, contractor agreement, contractor Worker's Comp affidavit (DIA Form 153), Homeowner Exemption Affidavit if owner-builder. ISD plans examiner review takes up to 5 weeks.
5. Coordinate Boston Water and Sewer Commission (BWSC) connection (~28d)
   Separate ADU water/sewer connection requires BWSC permit application at 980 Harrison Avenue. Boston's Combined Sewer Overflow (CSO) areas (much of South Boston, Dorchester, Roxbury) may trigger Stormwater Best Management Practices requirements per BWSC Stormwater Standards. CSO map at bwsc.org/cso. BWSC review separate from ISD plan review and runs in parallel.
6. Boston Fire Department review (if 3+ story structure or attached ADU adds occupancy load) (~14d)
   BFD Fire Prevention Division reviews ADUs in three-decker conversions where the third-floor unit was previously attic/storage. NFPA 13D residential sprinkler waiver is granted under MA state amendment to IRC R313 but BFD may impose hardwired interconnected smoke/CO alarms and a 1-hour fire-rated separation between ADU and principal dwelling per 780 CMR 9th edition Boston amendments.
7. Boston Landmarks Commission (BLC) review if in historic district (~75d)
   Beacon Hill, Back Bay, South End Landmark, Bay Village, Mission Hill Triangle, and 7 other Boston Landmark Districts require BLC Certificate of Appropriateness for any exterior alteration including detached ADU construction. Review takes 60-90 days; filing fee $250. BLC has authority to deny or condition approval on materials, fenestration, and massing.
8. Construction inspections via permitfinder.boston.gov (~60d)
   Inspections scheduled online: footing, foundation, frame, rough electrical (per Boston Electrical Inspector), rough plumbing/gas, insulation, fire-stopping, final. Boston ISD does foundation and final inspections; electrical inspections handled by Boston Electrical Inspector district office assignments (Boston is divided into 7 inspection districts).
9. Certificate of Occupancy and 1010 Mass Ave records filing (~15d)
   Final CO issued after all inspections close. Boston requires the new ADU dwelling unit be added to the city's residential property card (Boston Assessing Department updates) and registered with the Inspectional Services Department's Rental Registry (rentalregistration.boston.gov) within 30 days if the ADU will be rented.

• Long-term rental: yes Long-term rental of ADU explicitly permitted; Massachusetts owner-occupancy preemption (where applicable) makes ADU eligible for full landlord-tenant treatment.
• Short-term rental: with-restrictions STR rules vary by city. Boston regulates STRs separately from ADU permitting; check local STR ordinance and HOA covenants.
• Office rental: with-restrictions Detached office rental requires home occupation permit or rezoning.
• Home office: yes Home occupation permitted with restrictions on signage and customer traffic.
• Studio / workshop: yes Personal artist studio is a permitted accessory use.
• Agriculture: with-restrictions Limited urban agriculture permitted in residential zones; livestock varies by district.
• Relative support: yes Family-occupancy ADU explicitly permitted in single-family zones.

Staff: Will Cohen (Senior Zoning Reform Planner II - Boston Planning Department (BPDA successor); ADU code amendments lead) BPDAcommunications@boston.gov, Mayor's Office of Housing - ADU Program (Boston Home Center - ADU Financial Assistance Program (income-eligible homeowner ADU loans)) ADU@boston.gov, Boston Zoning Board of Appeal (ZBA) (Conditional use review for non-Mattapan ADU applications) zba@boston.gov, Boston Water and Sewer Commission (BWSC ADU connection / CSO compliance review) siteplans@bwsc.org, Boston Fire Department - Fire Prevention Division (Fire-rated separation review for attached ADUs in three-decker conversions) fpd@bfd.boston.gov, Boston Landmarks Commission (Certificate of Appropriateness review in 13 landmark/historic districts) BLC@boston.gov

• Water: Boston Water Utility · 21d connect · $4,500
• Sewer: Boston Sewer / Wastewater · 21d connect · $5,500
• Electric: Boston Electric Utility · 14d connect · $1,800
• Gas: Boston Gas Utility · 21d connect · $1,500

Realistic total: best 7mo · typical 11mo · worst 17mo

Modular pathway inspectors are experienced with modular

State ADU loans:

• MassHousing Accessory Dwelling Unit Loan Program (ADULP)
• Massachusetts Housing Partnership ADU Incentive Program
• Massachusetts Housing Partnership ADU Technical Assistance Program

Massachusetts has no HOA-ADU preemption; HOA covenants restricting ADUs are enforceable.

• other
  MA Coastal Zone Management overlay (CZM): East Boston, Charlestown, South Boston, and Dorchester waterfront parcels require Chapter 91 license review by MassDEP for fill or in-water work; ADUs in upland portions are typically exempt.
• historic-district
  Boston Landmarks Commission has authority over Beacon Hill, Back Bay, South End Landmark, Bay Village, Mission Hill Triangle, and 8 additional landmark districts. BLC Certificate of Appropriateness required for any exterior alteration before ISD permit.
• flood-zone
  Significant FEMA Special Flood Hazard Area exposure on Boston Harbor and tidal river frontage (Charles, Mystic, Neponset, Fort Point Channel). ADUs in Zone AE/VE require elevation certificate and 2 ft of freeboard above BFE per Boston Climate Resilient Design Standards.