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Quincy, MA Accessory Structures: ADU Rules (2026)

Few Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified September 2026

ADU rules in Quincy, MA, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

Code: Quincy ZO + MGL c. 40A §3
Maximum Size: 900 sq ft or 50% of principal, whichever is less
Minimum Size (detached): 320 sq ft
Allowed Types: Internal, addition, or detached
Additional Parking Required?: No

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Massachusetts under recent ADU streamlining laws. The Quincy, MA rules below cover local size, height, and setback requirements.

Summary

Quincy allows ADUs by right under MGL c. 40A §3 and the 2024 Affordable Homes Act. One ADU per single-family lot is allowed as internal, addition, or detached unit. Maximum size is 50% of principal dwelling or 900 sq ft, whichever is less. Minimum size is 320 sq ft for detached units.

No zoning ordinance or by-law shall prohibit, unreasonably restrict or require a special permit or other discretionary zoning approval for the use of land or structures for a single accessory dwelling unit, or the rental thereof, in a single-family residential zoning district; provided, that the use of land or structures for such accessory dwelling unit under this paragraph may be subject to reasonable regulations, including, but not limited to, 310 CMR 15.000 et seq., if applicable, site plan review, regulations concerning dimensional setbacks and the bulk and height of structures and may be subject to restrictions and prohibitions on short-term rental, as defined in section 1 of chapter 64G.

Source: City of Quincy OrdinancesView official code

Full Breakdown

Under Quincy ZO and MGL c. 40A §3 (as amended by the 2024 Affordable Homes Act), one ADU is allowed by right on any owner-occupied single-family lot. The ADU may be: (1) within the existing dwelling, (2) an addition to the dwelling, or (3) a detached unit. Maximum floor area: the lesser of 50% of the principal structure's gross floor area or 900 sq ft. Minimum size for detached ADUs: 320 sq ft. No additional parking mandates, no owner-occupancy requirements beyond MGL c. 40A §3 compliance, and no architectural matching requirements. All units must meet 780 CMR (Massachusetts Building Code) and state plumbing code.

Violations & Fines

ADUs not meeting size, setback, or building code requirements are subject to zoning enforcement.

Frequently Asked Questions

Can I build an ADU on my property in Quincy?

What are the size limits for an accessory dwelling unit in Quincy?

Code: Quincy ZO + MGL c. 40A §3. Maximum Size: 900 sq ft or 50% of principal, whichever is less. Minimum Size (detached): 320 sq ft. Allowed Types: Internal, addition, or detached.

Sources & Official References

[1]City of Quincy Ordinances

Other rules in Quincy

Parking Rules: Overnight ParkingSome Restrictions Shed & Carport RulesSome Restrictions Parking Rules: RV & Boat ParkingSignificant Restrictions Parking Rules: Towing & Impound RightsSome Restrictions Parking Rules: Abandoned VehiclesSome Restrictions Parking Rules: Snow Removal Parking RulesSome Restrictions Parking Rules: Loading ZonesSome Restrictions

All Quincy rules

How Quincy compares: Easiest Cities to Build an ADU·Compare Quincy to another location·View the Massachusetts accessory structures overview

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