Complete 2026 cost breakdown: construction, permits, financing, and expected rental ROI.
Calculate your Eugene ADU cost →Building an ADU in Eugene costs between $110,000-$285,000 for new construction, with per-square-foot costs averaging $150-$300. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $60,000-$150,000, while prefab/modular ADUs fall in between at $90,000-$230,000.
| Cost Category | Estimated Range |
|---|---|
| Architectural Plans | $3,000 – $15,000 |
| Permits & Fees | Valuation-based: building permit $953.34 plus $4.34 per $1,000 over $100,000, plan check 65% of that (waived for pre-approved plans), electrical $244.40, plumbing $571.40 for one bath, mechanical per appliance, plus 12% state surcharge (schedule effective July 1, 2025; a July 2026 schedule applies) |
| Impact Fees | System development charges of about $6,000-$10,000 per ADU (city SDC FAQ, Dec 2024; the ADU program page says budget about $7,000) for parks, stormwater and local/regional wastewater; the transportation SDC is reduced 100% for new ADUs. Payable at permit issuance or financed through the city over up to 10 years at prime plus 2%. EWEB charges a separate water SDC. Rates are indexed each July 1 |
| 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. We pass your request to up to 5 local builders serving Eugene, where we have them — free, no obligation.
Get Eugene builder quotes →Permit fees in Eugene are Valuation-based: building permit $953.34 plus $4.34 per $1,000 over $100,000, plan check 65% of that (waived for pre-approved plans), electrical $244.40, plumbing $571.40 for one bath, mechanical per appliance, plus 12% state surcharge (schedule effective July 1, 2025; a July 2026 schedule applies). The review timeline is Pre-approved plans: the city says site-specific plan review typically takes 3-4 weeks before the permit can issue (city ADU FAQ). Custom plans go through standard residential plan review; Eugene publishes no target time for it, with plan check: Building plan check is 65% of the building permit fee; waived when you build one of the city's pre-approved plans (only site-related review and fees remain). Impact fees are System development charges of about $6,000-$10,000 per ADU (city SDC FAQ, Dec 2024; the ADU program page says budget about $7,000) for parks, stormwater and local/regional wastewater; the transportation SDC is reduced 100% for new ADUs. Payable at permit issuance or financed through the city over up to 10 years at prime plus 2%. EWEB charges a separate water SDC. Rates are indexed each July 1. Pre-approved plans: Yes: the Pre-Approved ADU Plans Library has 11 detached plan sets from 287 to 795 sq ft (studio to 2 bedrooms). Ten are sold by their designers for $500 each; the city's own plan, The Joel, is a free download. All are pre-reviewed for building-code compliance, so the plan-review fee is not charged.
| 1-Bedroom Rent | $1,200-$1,500/month |
| 2-Bedroom Rent | $1,500-$1,900/month |
| Annual Rental Income (est.) | $16,200/year |
| Payback Period (est.) | 12.2 years |
| Short-Term Rental | Yes. Rentals under 30 days are allowed in a separate dwelling unit; the city requires free annual STR registration and a 4.5% transient room tax. City Council has an open review of STR regulations |
| Overall ROI Estimate | 6-9% gross rental yield (estimate) |
A typical ADU in Eugene generates approximately $16,200 per year in rental income based on average 1-bedroom rents. At an average construction cost of $197,500, the estimated payback period is 12.2 years — before accounting for the resale value the ADU adds, which an appraiser determines from comparable sales in Eugene 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 Eugene: $60,000-$150,000.
2. Prefab/modular ADUs offer predictable pricing and faster timelines. Average: $90,000-$230,000.
3. Pre-approved plans — available in Eugene, 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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