Quincy did not broadly allow ADUs before the state acted, but since the Affordable Homes Act took effect on February 2, 2025 it must — and its Inspectional Services guidelines (updated December 11, 2025) now permit one ADU by right in single-family zoning districts, whether internal, attached, or detached. ADUs are capped at 900 sq ft or 50% of the principal structure's gross floor area (whichever is less), detached ADUs are limited to one story with a 320 sq ft minimum, and short-term rental of ADUs is prohibited. ADUs are barred in Bus C/Ind A/Ind B districts, on lots subject to a variance, and below the FEMA 100-year base flood elevation — a real constraint in coastal Quincy.
Zoning & Size Requirements [1][2]
Yes — Quincy allows ADUs. A detached ADU can typically be up to 900 sq ft under current Massachusetts and Quincy zoning rules.
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| Allowed Zones | One ADU by right in single-family zoning districts (internal, addition, or detached); not allowed in Bus C, Ind A, or Ind B districts, or on a lot subject to a variance |
| Max Size (Detached) | 900 sq ft or 50% of the principal structure's gross floor area (per 760 CMR 71.02), whichever is less; minimum 320 sq ft for a detached ADU |
| Max Size (Attached) | 900 sq ft or 50% of the principal structure's gross floor area, whichever is less |
| Max Size (JADU) | No JADU category in Massachusetts law |
| Max Height | Detached ADUs limited to one story (city guideline) |
| Max Units | 1 ADU per lot; ADU may not be sold or owned separately from the principal dwelling, and no ADU is permitted below the FEMA 100-year base flood elevation |
Setback Requirements [1][2]
Quincy requires a rear setback of about 4 ft for a detached ADU, and one off-street parking space is required. Owner-occupancy is set by local rules (confirm with the city).
| Rear Setback | Detached ADUs must meet the principal-structure yard setbacks in QZO Table 4.1 — varies by district; Confirm with Quincy Inspectional Services |
| Side Setback | Per QZO Table 4.1 (district-specific) — Confirm with Quincy Inspectional Services |
| Front Setback | Per QZO Table 4.1 (district-specific) — Confirm with Quincy Inspectional Services |
| Parking Required | 1 additional off-street space required only if the ADU is outside a 1/2-mile radius of a transit station (Quincy has 4 Red Line stops); existing off-street parking may not be reduced to create the ADU |
| Owner Occupancy | Not allowed — prohibited statewide by the Affordable Homes Act effective Feb 2, 2025 |
| Min Lot Size | None stated in the ADU guidelines — underlying district lot standards apply; Confirm with Quincy Inspectional Services |
Permit Process & Fees [3]
An ADU permit in Quincy typically costs Valuation-based building permit fee — Confirm with Quincy Inspectional Services and takes Standard building-permit review; typically 4-8 weeks — Confirm with Quincy Inspectional Services, through a ministerial, by-right review.
| Approval Process | By-right building permit through Inspectional Services (1305 Hancock St, 617-376-1000): submit a site plan showing drainage, utilities, and existing/proposed parking plus architectural drawings; must comply with QZO §3.4, 780 CMR (state building code), 527 CMR 18 fire-access rules, the state plumbing code, and Quincy DPW utility regulations |
| Review Timeline | Standard building-permit review; typically 4-8 weeks — Confirm with Quincy Inspectional Services |
| Permit Fees | Valuation-based building permit fee — Confirm with Quincy Inspectional Services |
| Impact Fees | None listed in the ADU guidelines — Confirm with Quincy Inspectional Services |
| Plan Check | Site plan (drainage, utilities, parking) + architectural drawings required; flood-zone screening against the FEMA 100-Year Flood Hazard Map for Quincy |
| Pre-Approved Plans | None — Quincy does not offer a pre-approved ADU plan library |
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Construction Costs [4]
Building an ADU in Quincy typically costs $250,000-$425,000 ($350-$550 per sq ft); a garage conversion runs $150,000-$250,000.
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| Average Build Cost | $250,000-$425,000 |
| Cost per Sq Ft | $350-$550 |
| Garage Conversion | $150,000-$250,000 |
| Prefab ADU (Installed) | $180,000-$350,000 installed (site work, foundation, and utility connections extra — confirm with manufacturer) |
Finance Your ADU Project
Most ADU projects are funded through HELOCs, construction loans, or cash-out refinancing. Compare rates from top lenders.
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Rental Income Potential [5][6]
A 2-bedroom ADU in Quincy rents for around $2,700-$3,300/mo, an estimated 5-8% annual return.
| Avg Rent (1 Bedroom) | $2,200-$2,700/mo |
| Avg Rent (2 Bedroom) | $2,700-$3,300/mo |
| Short-Term Rental | No — Quincy's ADU guidelines expressly prohibit using an ADU as a short-term rental |
| Est. Annual ROI | 5-8% annual return |
Explore Prefab ADU Options
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Recent Law Changes
What's Changed Recently
- Dec 11, 2025 — Quincy Inspectional Services republished updated ADU guidelines: one-story limit for detached ADUs, 320 sq ft detached minimum, FEMA flood-elevation bar, no separate ownership, STR ban
- Feb 28, 2025 — Quincy issued its first ADU guidelines implementing the state law shortly after it took effect
- Feb 2, 2025 — Massachusetts Affordable Homes Act §8 and 760 CMR 71 took effect statewide: ADUs by right in single-family districts, no owner-occupancy requirement, parking capped at 1 space (none within 1/2 mile of transit)
Tips for Building an ADU in Quincy
- Check the FEMA 100-Year Flood Hazard Map first — large parts of coastal Quincy (Houghs Neck, Germantown, Squantum, Adams Shore) sit in flood zones where ADUs below base flood elevation are prohibited
- Living within 1/2 mile of North Quincy, Wollaston, Quincy Center, or Quincy Adams Red Line stations means no ADU parking space can be required
- Detached ADUs must be one story and meet full principal-building setbacks (QZO Table 4.1) — an internal basement or attic conversion avoids both constraints
- Don't plan on Airbnb income: Quincy bans short-term rental of ADUs outright — underwrite with long-term rents ($2,200-$2,700 for a 1BR)
- If your lot was ever granted a zoning variance, you cannot add an ADU by right — pull your lot's history with Inspectional Services before spending on design
- Budget for 4-ft frost-depth foundations and avoid winter pours; utility connections must satisfy Quincy DPW regulations, so get DPW sign-off early
ADU Builders in Quincy
Looking for an ADU builder in Quincy? ADU projects need a contractor experienced with local zoning, the permit process, and utility connections — not every general contractor has built one. We match Quincy homeowners with experienced local ADU contractors who provide free, no-obligation quotes. Getting at least three bids typically saves 20-40% on the same scope.
Sources & References
All data on this page is sourced from official government records and verified market data. View our full methodology.
- Accessory Dwelling Units — Quincy Inspectional Services (Guidelines December 11, 2025) city_website — Accessed 2026-07-10
- Accessory Dwelling Units — Mass.gov (EOHLC) state_statute — Accessed 2026-07-10
- Accessory Dwelling Units — Quincy Inspectional Services (Guidelines December 11, 2025) city_website — Accessed 2026-07-10
- How Much Does It Cost to Build an ADU in Boston? — Horizon ADU news_media — Accessed 2026-07-10
- Average Rent in Quincy, MA — Zumper Rent Research news_media — Accessed 2026-07-10
- Average Rent in Quincy, MA — RentHop news_media — Accessed 2026-07-10
Frequently Asked Questions
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