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Charlestown ADU feasibility

Charlestown is in Boston, which is outside the statewide by-right ADU law.

Not legal advice. This is not legal advice. It is a screening summary of the Affordable Homes Act (Chapter 150 of the Acts of 2024), the EOHLC regulations at 760 CMR 71.00, and the local pages cited here. It is not a permit or a zoning opinion. EOHLC does not answer questions about a specific property. Setbacks, lot coverage, the building code, the fire code, Title 5 septic rules (310 CMR 15.000), wetlands, flood zones, and historic review can change the outcome. Confirm the parcel with the city or town and a licensed professional before you spend money on plans. HLC has proposed revisions to 760 CMR 71.00; public comment closed on October 9, 2026. This screen uses the regulations published in the Massachusetts Register on January 31, 2025, which took effect February 2, 2025, not that draft.

Rules cited for Charlestown

The Affordable Homes Act amended Chapter 40A. EOHLC states that every Massachusetts city and town except Boston is subject to that law.
Boston allows one internal ADU on an owner-occupied 1-, 2-, or 3-family house, inside the existing footprint, with no added floor area. Condominiums and LLCs are not eligible.
An attached addition or a detached building needs Zoning Board of Appeal relief, except in Mattapan.
Boston requires the owner to live in the house. The state ban on owner-occupancy rules does not apply in Boston.
This checker does not cite a Boston square-foot maximum or a Boston parking waiver.

Massachusetts address

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Town

Lot size (sq ft)

Existing house gross floor area (sq ft)

Include basements with legal ceiling height. Exclude crawl spaces, garages, attics, and enclosed porches.

Lot type

Single-family zoningThe district allows a single-family house by right.Single-family zoning, within 0.5 miles of a transit stationAny part of the lot is within 0.5 miles of a commuter rail station, subway station, ferry terminal, or a regular bus station. A flag stop does not count.Single-family zoning in a local historic districtZoning may still allow the unit. A historic district can require a separate design review.District allows single-family homes, and the house is a 2- or 3-familyThe by-right unit is not limited to lots that contain only a single-family house.Zoning does not allow single-family homesBusiness or industrial districts that do not allow a single-family house are outside the state by-right rule.

Does the owner live in this Boston house?

Boston requires owner occupancy. Other Massachusetts cities and towns cannot.

Charlestown ADU feasibility

Rules cited for Charlestown

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