Portland, OR · Zoning rules · Updated 2026
Portland ADU Rules — What You Can Build
Portland allows accessory dwelling units on most residential lots, with a size cap that scales with your primary dwelling. Portland's small-ADU SDC waiver (in effect through ~2028) makes ≤800 SF ADUs meaningfully more profitable than larger ones.
The rule
Portland allows ADUs up to 800 SF or 75% of the primary dwelling, whichever is greater. ADUs over 800 SF lose the small-ADU SDC waiver.
Source: Portland City Code Title 33.205.040.B
How big can your ADU be?
| Primary dwelling | Maximum ADU size | ADU as % of primary |
|---|---|---|
| 1,000 SF house | 800 SF | 80% |
| 1,500 SF house | 1,125 SF | 75% |
| 2,000 SF house | 1,500 SF | 75% |
| 2,500 SF house | 1,500 SF | 60% |
| 3,500 SF house | 1,500 SF | 43% |
Sizes reflect the code rule only. Site-specific setbacks, coverage limits, and overlay zones may reduce buildable envelope further.
Analyze your specific Portland property
Drop an address to see the exact ADU size your lot allows, plus fourplex, cottage cluster, and middle-housing options. Includes construction cost estimates, exit values, ROI, and cited code sections for every constraint.
Analyze a Portland addressBeyond the ADU rule
Setbacks + lot coverage
Each zoning district has its own front, side, and rear setbacks plus a lot-coverage cap. Our analyzer applies your zone’s actual limits automatically.
Parking requirements
Many jurisdictions have reduced ADU parking mandates under state law. We flag when your lot requires additional parking spaces.
Overlay zones
Historic districts, floodplains, and design-review overlays can override base zoning. We check the current overlay map for your specific address.
SDCs + permit fees
System Development Charges vary by jurisdiction and ADU size. Portland waives SDCs on ADUs ≤ 800 SF through ~2028.