ADU rules in Quincy

Quincy's zoning ordinance has no ADU provision at all: a search of the entire Quincy Code returns zero hits for 'accessory dwelling', 'accessory apartment', 'accessory unit' or 'ADU', and Appendix A (Table of Use Regulations) lists no such use. Detached backyard ADUs therefore proceed under the statewide protected-use right effective February 2, 2025, administered by the Inspectional Services Department under its Accessory Dwelling Unit Guidelines dated December 11, 2025: 'One ADU, whether within the dwelling, or addition, or detached, is allowed in single-family zoning districts.' The guidelines exclude only the Business C, Industrial A and Industrial B districts (the three districts where Appendix A does not allow a single-family dwelling) plus 'a lot subject to a variance'. A detached unit must meet the yard setbacks in Table 4.1, is limited to one story, must satisfy 527 CMR § 18 for fire access, and must be at least 320 square feet; no ADU may be built below the FEMA 100-year base flood elevation, which bites across Quincy's coastal neighborhoods.

The same December 11, 2025 guideline sentence covers an ADU 'within the dwelling, or addition', so basement conversions, internal units and additions stand on the same by-right footing as detached cottages. 760 CMR 71.03(2)(e) independently forbids a municipality from requiring that a protected ADU be attached to or detached from the principal dwelling, so Quincy could not favor one form over the other. The city's online permit application (OpenGov record type 6585, 'Accessory Dwelling Unit') describes itself as being 'for the addition of an Accessory Dwelling Unit to an existing or new single-family home.' Worth knowing before starting an internal conversion: Zoning Ordinance § 10.2 provides that 'Where a dwelling has more than one kitchen, the burden of proof shall be upon the owner to show that the premises constitutes not more than one dwelling unit', so a second kitchen is best created through the ADU permit rather than informally.

The ISD guidelines adopt the state ceiling verbatim: 'The floor area of an ADU is limited to 50% of the gross floor area of the principal structure as defined in section 760CMR section 71.02 or 900 s.f., whichever is less.' Gross floor area for this purpose is the 760 CMR 71.02 definition (all stories of compliant ceiling height, including basements and lofts, but excluding crawl spaces, garage parking areas, attics and enclosed porches), which is not the same as the Zoning Ordinance § 10.2 definition. Quincy adds a minimum the state does not impose: a detached ADU must be at least 320 square feet. Detached units are also held to one story, while Table 4.1 allows a principal dwelling in Residence A up to 2.5 stories.

Nothing in the ISD guidelines requires the owner to live on the property, and no such requirement would be enforceable: 760 CMR 71.03(2)(a) lists 'Owner-Occupancy Requirements' among the prohibited regulations, and MGL c. 40A § 3 provides that the use of land or structures for a protected ADU 'shall not require owner occupancy of either the accessory dwelling unit or the principal dwelling.' Because Quincy's zoning ordinance never had an ADU section, there is no legacy owner-occupancy clause on the books to create confusion. The guidelines do impose a related but different condition: 'ADUs shall not have separate ownership', meaning the ADU cannot be condominiumized or sold away from the principal dwelling. Occupancy of the ADU also cannot be limited to relatives, since 760 CMR 71.03(2)(c) bars use and occupancy restrictions keyed to familial relationship.

The ISD guidelines track the state limits exactly: 'One additional off-street parking space is required if the ADU is outside a 0.5-mile radius of a Transit Station. Off-street parking may not be reduced due to the creation of an ADU. Existing off-street parking must comply with section 5.1 of the Zoning Ordinance.' Under 760 CMR 71.03(2)(b) no additional space at all may be required where any portion of the lot lies within a half mile of a transit station, and 760 CMR 71.02 defines a transit station broadly to include any MBTA subway stop, a year-round commuter rail station, a ferry terminal, and any point of embarkation for a Transit Authority bus; with four Red Line stations (North Quincy, Wollaston, Quincy Center, Quincy Adams), Quincy Center commuter rail and dense MBTA bus service, much of the city sits in the no-parking-required band. Quincy's base parking table in § 5.1.8 (2 spaces per dwelling with 1 to 2 bedrooms in Residence A, 2 per unit in Residence B and C) cannot be applied to a protected ADU. Spaces already serving the principal dwelling must be kept and must still meet § 5.1's location, setback and dimensional rules.

Administrative and ministerial: the ADU is handled by Inspectional Services on a building permit through the city's dedicated 'Accessory Dwelling Unit' application in its OpenGov permitting portal, with fees under Code § 150-3 (Building fees). No special permit or Zoning Board of Appeals hearing is involved, and Zoning Ordinance § 9.5.1 does not list ADUs among the uses requiring Planning Board site plan review (its residential trigger starts at three or more dwelling units). The guidelines do require a submittal-level site plan showing 'drainage, utilities, architectural drawings, and existing/proposed parking', which is a plan-review requirement rather than a discretionary approval. MGL c. 40A § 3 and 760 CMR 71.03(1) independently bar Quincy from requiring a special permit, variance or other discretionary zoning approval for the first protected ADU on a lot; a second ADU on the same lot would require a special permit under 760 CMR 71.03(5), and Quincy has no local provision allowing one.

Renting the ADU on a normal lease is exactly what the state law protects, and Quincy imposes no primary-residence or tenant-relationship test. Transient use is banned outright: the ISD guidelines say 'An ADU may not be used as a Short-Term Rental.' A short-term rental is a rental for not more than 31 consecutive days under MGL c. 64G § 1, and both MGL c. 40A § 1A and 760 CMR 71.03(3)(c) expressly permit municipalities to restrict or prohibit short-term rental of protected ADUs, so the ban is within Quincy's authority. The guidelines separately provide that 'ADUs shall not have separate ownership', so the unit cannot be sold or condominiumized apart from the principal dwelling. Quincy's zoning treats short-term residential rentals as their own use in any event: § 6.12 and Appendix A prohibit them in Residence A and require a Zoning Board of Appeals special permit in every other district.