Portland, OR Accessory Structures: ADU Rules (2026)
ADU rules in Portland, OR, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- Max size
- 75% of house or 800 sq ft
- Front setback
- 40 ft, or behind rear wall
- Zones allowed
- RF, R20-R2.5, multi-dwelling, C, EX
- Permit
- Building permit required, § 33.700.005
Summary
Portland caps accessory dwelling units at 800 square feet or 75% of the primary home's living area, whichever is smaller, and requires a 40-foot front setback or placement behind the main house's rear wall.
1. Maximum size. The living area of the accessory dwelling unit may be no more than 75 percent of the living area of the primary dwelling unit or 800 square feet of living area, whichever is less. This maximum size standard does not apply when the basement of a primary dwelling unit is converted to an accessory dwelling unit and the primary dwelling unit has been on the site for at least 5 years. The size measurements are based on what the square footage of the primary dwelling unit and accessory dwelling unit will be after the accessory dwelling unit is created. When the primary dwelling unit is a duplex, the size of the accessory dwelling unit may be no more than 75 percent of the living area of the larger of the two primary units or 800 square feet of living area, whichever is less.
2. Setbacks. Detached and connected accessory dwelling units must be:
a. Set back 40 feet from the front lot line; or
b. Located behind the rear building wall of the primary dwelling. For the purpose of this regulation, the rear wall of the primary dwelling unit is the wall furthest from the wall with the main entrance to the street.
3. Detached and connected accessory dwelling units must meet the development standards for covered accessory structures in the base zone.
4. Visitability.
Full Breakdown
Portland City Code Chapter 33.205 sets the zoning standards an accessory dwelling unit must meet before the city issues a building permit under Section 33.700.005. In the RF, R20 through R2.5, multi-dwelling, C, and EX zones, one or two ADUs are allowed depending on lot size and whether the site holds a house, duplex, or manufactured home. Each unit is capped at 75 percent of the primary dwelling's living area or 800 square feet, whichever is less, and must sit at least 40 feet from the front lot line or behind the primary structure's rear wall. Some configurations, including sites with two ADUs or an ADU on a duplex lot, must also meet visitability standards for entry, bathroom, and doorway access.
Violations & Fines
Violating Title 33's ADU standards is unlawful under Portland City Code § 33.700.030. The Bureau of Planning and Sustainability issues a written notice of violation and can pursue enforcement under Chapter 3.30 and Title 22 of the City Code.
Frequently Asked Questions
How big can a Portland ADU be?
Where does a Portland ADU have to be set back?
Sources & Official References
Other rules in Portland
How Portland compares: Easiest Cities to Build an ADU·Compare Portland to another location·View the Oregon accessory structures overview
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ADU Rules in Nearby Cities
How other cities in Multnomah County handle adu rules.