An ADU builder in Quincy is a licensed contractor who designs and constructs accessory dwelling units — detached backyard units, garage conversions, attached additions, and junior ADUs (JADUs). Because an ADU is a complete second dwelling, the builder coordinates foundation, framing, plumbing, electrical, and HVAC work and pulls it through Quincy's permit process and utility connections. Not every general contractor has built one, so the right builder is one with ADU-specific experience in Massachusetts.
What ADU Builders Cost in Quincy [4]
Based on our Quincy cost data, expect the following ranges from local ADU builders. Quotes for the same scope typically vary 20-40% between contractors, so getting at least three bids is the single best way to control cost.
| New Detached ADU (all-in) | $250,000-$425,000 |
| Cost per Sq Ft | $350-$550 |
| Garage Conversion | $150,000-$250,000 |
| Prefab / Modular ADU (installed) | $180,000-$350,000 installed (site work, foundation, and utility connections extra — confirm with manufacturer) |
| City Permit & Plan Review | Valuation-based building permit fee — Confirm with Quincy Inspectional Services |
| Impact Fees | None listed in the ADU guidelines — Confirm with Quincy Inspectional Services |
For a full line-item breakdown, see our Quincy ADU cost guide. To confirm what you're allowed to build before you hire, review the Quincy ADU rules (max detached size: 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; owner-occupancy: Not allowed — prohibited statewide by the Affordable Homes Act effective Feb 2, 2025).
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How to Vet an ADU Builder in Quincy
- License: Confirm a current contractor's license in Massachusetts and that it's in good standing. Ask for the license number and verify it with the state board.
- ADU-specific experience: Ask how many ADUs they've completed in or near Quincy and request addresses or photos. ADU permitting and setbacks differ from a kitchen remodel.
- Portfolio & references: Get references from recent ADU clients and, if possible, visit a finished unit.
- Insurance: Verify general liability and workers' compensation coverage. Ask for a certificate of insurance.
- Written, detailed bid: Insist on an itemized, fixed-price or clearly-scoped bid — not a verbal estimate. It should state whether permits (Valuation-based building permit fee — 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), and impact fees (None listed in the ADU guidelines — Confirm with Quincy Inspectional Services) are included.
- Permit handling: Confirm they manage Quincy's permit 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", typically Standard building-permit review; typically 4-8 weeks — Confirm with Quincy Inspectional Services) and who is responsible if revisions are required.
- Payment schedule: Avoid large upfront payments. A reasonable schedule ties payments to completed milestones.
Questions to Ask Before You Hire
- How many ADUs have you built in Quincy in the last two years?
- Is your bid fixed-price, and what would trigger a change order?
- Are permits, plan check, and utility connection fees included?
- What's a realistic timeline, including permit review (Standard building-permit review; typically 4-8 weeks — Confirm with Quincy Inspectional Services) and construction?
- Who is my point of contact and how are delays communicated?
- What warranty do you provide on workmanship?
- Can you share three recent Massachusetts ADU client references?
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