Complete 2026 cost breakdown: construction, permits, financing, and expected rental ROI.
Calculate your Fontana ADU cost →Building an ADU in Fontana costs between $160,000-$270,000 for new construction, with per-square-foot costs averaging $200-$250. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $75,000-$130,000, while prefab/modular ADUs fall in between at $80,000-$140,000.
| Cost Category | Estimated Range |
|---|---|
| Architectural Plans | $3,000 – $15,000 |
| Permits & Fees | Waived for ADUs under 750 sq ft; fee applies for larger units (amount varies) |
| Impact Fees | Waived for units under 750 sq ft (SB 13); proportional for larger units |
| 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 Fontana — no obligation.
Get Fontana builder quotes →Permit fees in Fontana are Waived for ADUs under 750 sq ft; fee applies for larger units (amount varies). The review timeline is ~60 days with pre-approved plans, with plan check: Included in 60-day timeline; faster with pre-approved designs. Impact fees are Waived for units under 750 sq ft (SB 13); proportional for larger units. Pre-approved plans: Yes - Fontana's Standard ADU Plans program (AB 1332) offers pre-approved plans with designer contacts.
| 1-Bedroom Rent | $1,300-$1,700/month |
| 2-Bedroom Rent | $1,700-$2,200/month |
| Annual Rental Income (est.) | $18,000/year |
| Payback Period (est.) | 11.9 years |
| Short-Term Rental | Subject to local ordinance; verify before planning |
| Overall ROI Estimate | 7-10 year payback |
A typical ADU in Fontana generates approximately $18,000 per year in rental income based on average 1-bedroom rents. At an average construction cost of $215,000, the estimated payback period is 11.9 years — before accounting for the resale value the ADU adds, which an appraiser determines from comparable sales in Fontana 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 Fontana: $75,000-$130,000.
2. Prefab/modular ADUs offer predictable pricing and faster timelines. Average: $80,000-$140,000.
3. Pre-approved plans — available in Fontana, which can save $3,000-$10,000 in design costs and 2-3 months in review time.
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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