Complete 2026 cost breakdown: construction, permits, financing, and expected rental ROI.
Calculate your Folsom ADU cost →Building an ADU in Folsom costs between $150,000-$300,000 for new construction, with per-square-foot costs averaging $250-$400. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $80,000-$150,000, while prefab/modular ADUs fall in between at $120,000-$250,000.
| Cost Category | Estimated Range |
|---|---|
| Architectural Plans | $3,000 – $15,000 |
| Permits & Fees | Standard building permit and plan check fees; a planning application fee applies only if design review is required — confirm amounts with Folsom Community Development |
| Impact Fees | No city impact fees for ADUs of 750 sq ft or less (or JADUs ≤500 sq ft); proportional to primary dwelling size above 750 sq ft |
| 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 Folsom — no obligation.
Get Folsom builder quotes →Permit fees in Folsom are Standard building permit and plan check fees; a planning application fee applies only if design review is required — confirm amounts with Folsom Community Development. The review timeline is Completeness check within 15 business days; approval or denial within 60 days of a complete application — deemed approved if the city misses the deadline (codified per SB 543), with plan check: Combined design review + building permit saves an estimated 3-4 weeks versus the old two-step process. Impact fees are No city impact fees for ADUs of 750 sq ft or less (or JADUs ≤500 sq ft); proportional to primary dwelling size above 750 sq ft. Pre-approved plans: No city-published pre-approved plan library found — confirm options with Folsom Community Development.
| 1-Bedroom Rent | $1,900-$2,150/month |
| 2-Bedroom Rent | $2,300-$2,600/month |
| Annual Rental Income (est.) | $24,300/year |
| Payback Period (est.) | 9.3 years |
| Short-Term Rental | No — rentals must be 30 days or longer (FMC 17.105.070); ADUs cannot be vacation rentals |
| Overall ROI Estimate | 6-9% annual return |
A typical ADU in Folsom generates approximately $24,300 per year in rental income based on average 1-bedroom rents. At an average construction cost of $225,000, the estimated payback period is 9.3 years — before accounting for the resale value the ADU adds, which an appraiser determines from comparable sales in Folsom 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 Folsom: $80,000-$150,000.
2. Prefab/modular ADUs offer predictable pricing and faster timelines. Average: $120,000-$250,000.
3. Pre-approved plans — Folsom does not offer a pre-approved/standard ADU plan program yet, so budget for custom architectural plans (typically $3,000-$15,000).
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.
Compare prices from local ADU contractors in your area. Free, no-obligation estimates.
Find ADU Contractors →