Complete 2026 cost breakdown: construction, permits, financing, and expected rental ROI.
Calculate your Portland ADU cost →Building an ADU in Portland costs between $150,000-$300,000 for new construction, with per-square-foot costs averaging $125-$250. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $70,000-$160,000, while prefab/modular ADUs fall in between at $100,000-$240,000.
| Cost Category | Estimated Range |
|---|---|
| Architectural Plans | $3,000 – $15,000 |
| Permits & Fees | ~$1,900 permit and plan review; plus System Development Charges (SDCs) of about $19,000 - see impact fees |
| Impact Fees | SDCs total roughly $18,900 for a detached ADU (Parks ~$7,100, Sewer ~$6,600, Transportation ~$2,900, Water ~$2,300); waivable through Portland's ADU SDC Waiver if the unit is not used as a short-term rental (10-year covenant, application required) |
| 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 Portland — no obligation.
Get Portland builder quotes →Permit fees in Portland are ~$1,900 permit and plan review; plus System Development Charges (SDCs) of about $19,000 - see impact fees. The review timeline is 30-45 days, with plan check: 1-2 weeks. Impact fees are SDCs total roughly $18,900 for a detached ADU (Parks ~$7,100, Sewer ~$6,600, Transportation ~$2,900, Water ~$2,300); waivable through Portland's ADU SDC Waiver if the unit is not used as a short-term rental (10-year covenant, application required). Pre-approved plans: Extensive pre-approved library available.
| 1-Bedroom Rent | $1,400-$1,900/month |
| 2-Bedroom Rent | $1,800-$2,600/month |
| Annual Rental Income (est.) | $19,800/year |
| Payback Period (est.) | 11.4 years |
| Short-Term Rental | Yes, with registration |
| Overall ROI Estimate | 6-9% annual return |
A typical ADU in Portland generates approximately $19,800 per year in rental income based on average 1-bedroom rents. At an average construction cost of $225,000, the estimated payback period is 11.4 years — before accounting for the resale value the ADU adds, which an appraiser determines from comparable sales in Portland 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 Portland: $70,000-$160,000.
2. Prefab/modular ADUs offer predictable pricing and faster timelines. Average: $100,000-$240,000.
3. Pre-approved plans — available in Portland, 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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