Portland is one of America's most ADU-friendly cities, with streamlined approval processes and generous size allowances. The city allows both detached and attached ADUs with minimal setback requirements, making it an ideal market for ADU investment.
Zoning & Size Requirements [1][2]
| Allowed Zones | All residential zones |
| Max Size (Detached) | 800 sq ft or 75% of primary (whichever is less) |
| Max Size (Attached) | 1,000 sq ft |
| Max Size (JADU) | 800 sq ft |
| Max Height | 20 ft (outside setbacks); 15 ft (within setbacks) |
| Max Units | 2 ADUs per lot (1 detached + 1 attached) |
Setback Requirements [1][2]
| Rear Setback | 5 feet |
| Side Setback | 0 feet with easement |
| Front Setback | 0 feet (alley lot) |
| Parking Required | Optional |
| Owner Occupancy | Not required |
| Min Lot Size | 3,500 sq ft |
Permit Process & Fees [3]
| Approval Process | By-right approval (no variance needed) |
| Review Timeline | 30-45 days |
| Permit Fees | $1,500-$2,500 |
| Impact Fees | Minimal |
| Plan Check | 1-2 weeks |
| Pre-Approved Plans | Extensive pre-approved library available |
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Construction Costs [4][5]
| Average Build Cost | $150,000-$300,000 |
| Cost per Sq Ft | $125-$250 |
| Garage Conversion | $70,000-$160,000 |
| Prefab ADU (Installed) | $100,000-$240,000 |
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Rental Income Potential [6][7]
| Avg Rent (1 Bedroom) | $1,400-$1,900/mo |
| Avg Rent (2 Bedroom) | $1,800-$2,600/mo |
| Short-Term Rental | Yes, with registration |
| Est. Annual ROI | 6-9% annual return |
Explore Prefab ADU Options
Prefab ADUs can save 20-40% vs. traditional construction and cut build time in half.
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Recent Law Changes
What's Changed Recently
- HB 2001 compliance expanding (2026): All cities >2,500 pop must allow ADUs by right
- Portland streamlined ADU permits: 30-day turnaround for pre-approved plans (2026)
- New state ADU financing pilot: Low-interest loans for owner-occupants (2026)
- Oregon reduced system development charges for ADUs under 800 sq ft (2026)
Tips for Building an ADU in Portland
- Portland's by-right approval is industry-leading; fastest permitting in the nation
- Pre-approved plans available online; can fast-track your project
- Rental market is strong with good long-term tenant base
- Multiple ADU types allowed on single lot; maximum flexibility for design
Sources & References
All data on this page is sourced from official government records and verified market data. View our full methodology.
- ADU Zoning Requirements | Portland.gov Planning Department — Accessed 2026-02-24
- Portland Zoning Code 33.205 — Accessory Dwelling Units Municipal Code — Accessed 2026-02-24
- ADU Permits | Portland.gov Planning Department — Accessed 2026-02-24
- HomeAdvisor — ADU Construction Cost Data Market Data — Accessed 2026-02-24
- Angi — Local ADU Contractor Costs Market Data — Accessed 2026-02-24
- Zillow Rental Manager — Market Rent Data Market Data — Accessed 2026-02-24
- HUD Fair Market Rents Government Data — Accessed 2026-02-24
- Accessory Dwelling Units (ADUs) | Portland.gov Planning Department — Accessed 2026-02-24
- Oregon ADU Regulations — DLCD Government Data — Accessed 2026-02-24
Frequently Asked Questions
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