Complete 2026 cost breakdown: construction, permits, financing, and expected rental ROI.
Calculate your Quincy ADU cost →Building an ADU in Quincy costs between $250,000-$425,000 for new construction, with per-square-foot costs averaging $350-$550. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $150,000-$250,000, while prefab/modular ADUs fall in between at $180,000-$350,000 installed (site work, foundation, and utility connections extra — confirm with manufacturer).
| Cost Category | Estimated Range |
|---|---|
| Architectural Plans | $3,000 – $15,000 |
| Permits & Fees | Valuation-based building permit fee — Confirm with Quincy Inspectional Services |
| Impact Fees | None listed in the ADU guidelines — Confirm with Quincy Inspectional Services |
| Site Prep & Foundation | $10,000 – $35,000 |
| Framing & Structure | $15,000 – $45,000 |
| Plumbing | $8,000 – $20,000 |
| Electrical | $5,000 – $15,000 |
| HVAC | $3,000 – $8,000 |
| Interior Finishes | $15,000 – $40,000 |
Quotes for the same ADU commonly vary 20–40% between builders. Get up to 3 free quotes from ADU builders serving Quincy — no obligation.
Get Quincy builder quotes →Permit fees in Quincy are Valuation-based building permit fee — Confirm with Quincy Inspectional Services. The review timeline is Standard building-permit review; typically 4-8 weeks — Confirm with Quincy Inspectional Services, with plan check: Site plan (drainage, utilities, parking) + architectural drawings required; flood-zone screening against the FEMA 100-Year Flood Hazard Map for Quincy. Impact fees are None listed in the ADU guidelines — Confirm with Quincy Inspectional Services. Pre-approved plans: None — Quincy does not offer a pre-approved ADU plan library.
| 1-Bedroom Rent | $2,200-$2,700/month |
| 2-Bedroom Rent | $2,700-$3,300/month |
| Annual Rental Income (est.) | $29,400/year |
| Payback Period (est.) | 11.5 years |
| Short-Term Rental | No — Quincy's ADU guidelines expressly prohibit using an ADU as a short-term rental |
| Overall ROI Estimate | 5-8% annual return |
A typical ADU in Quincy generates approximately $29,400 per year in rental income based on average 1-bedroom rents. At an average construction cost of $337,500, the estimated payback period is 11.5 years — before accounting for the resale value the ADU adds, which an appraiser determines from comparable sales in Quincy and varies by market (often less than build cost).
1. Garage conversions save 40-60% vs new construction since the shell already exists. Average cost in Quincy: $150,000-$250,000.
2. Prefab/modular ADUs offer predictable pricing and faster timelines. Average: $180,000-$350,000 installed (site work, foundation, and utility connections extra — confirm with manufacturer).
3. Pre-approved plans — available in Quincy, which can save $3,000-$10,000 in design costs and 2-3 months in review time. See which cities offer pre-approved ADU plans.
4. State grants — California's CalHFA ADU grant (up to $40K) is currently paused; check calhfa.ca.gov/adu for status and your state for active programs.
5. Get multiple bids — ADU contractor pricing varies 20-40% for the same project. We recommend getting at least 3 quotes.
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