ADU Rules in Portland, Oregon

Portland, Oregon's largest city and Multnomah County seat, has long been a national leader in ADU (Accessory Dwelling Unit) policy reform. The city voluntarily eliminated owner-occupancy requirements and waived system development charges for ADUs years before Oregon statewide law mandated these changes. Portland's progressive zoning approach, combined with Metro regional government oversight and state-level housing reforms, makes it one of the most ADU-friendly jurisdictions in the country.

Oregon Statewide ADU Law — Critical Context

Two landmark Oregon laws govern ADUs statewide and directly affect what Portland can and cannot require:

Oregon HB 2001 (2019) requires cities with populations over 10,000 to allow middle housing — including duplexes, triplexes, fourplexes, and cottage clusters — in all residential zones. This effectively ended single-family-only zoning in Portland and throughout Oregon.

Oregon SB 1051 (2017) prohibits cities with populations over 2,500 (and counties over 15,000) from banning ADUs in areas zoned for single-family dwellings; the operative date was July 1, 2018. Subsequent Oregon legislation (e.g., SB 8 of 2021 on affordable-housing siting) has continued to shape ADU and middle-housing rules. Always consult Portland Permitting & Development and Oregon DLCD for current standards.

What Portland Allows

Portland's Title 33 Zoning Code permits the following ADU types on most residential lots:

• Detached ADU: A standalone structure separate from the primary dwelling. Generally up to 800–1,000 square feet depending on zone and lot coverage.
• Attached ADU: An addition built onto the primary dwelling, sharing at least one wall.
• Interior ADU (Conversion): Converting existing space within the primary structure — basement, attic, or unused rooms — into a separate dwelling unit.
• Garage Conversion: Converting an existing detached garage into a livable ADU unit.

One ADU is permitted per single-family lot by right. Portland's zoning code, updated following HB 2001, also allows multi-unit configurations that go beyond traditional ADU limits on many lots.

Size and Setback Standards

Oregon and Portland law set both maximum ADU size limits and design rules. Specific size, height, and setback limits are set by Portland's Title 33 Zoning Code — verify the current values directly with Portland Permitting & Development before designing. Detached ADUs in Portland's R1 and R2 zones typically must observe:

• Rear setback: 5 feet minimum
• Side setback: 5 feet minimum
• Height: Up to 20 feet for detached ADUs in many zones

Structures being converted from existing legal nonconforming buildings may maintain existing setbacks even if they would not comply with current standards for new construction.

Special Considerations for Portland Properties

Seismic hazard: Portland sits on the Willamette Valley floor and is subject to shaking from the Cascadia Subduction Zone offshore. Oregon DOGAMI (Department of Geology and Mineral Industries) maps high liquefaction potential in many Portland neighborhoods near the Willamette River. New ADU construction must meet Oregon's seismic building code standards; soft-story retrofits may be required for older structures being converted.

Flood zones: Portions of Portland near the Willamette River and Columbia River Slough are in FEMA flood hazard zones. ADU construction in these areas may require flood-resistant construction, elevated foundations, or FEMA permits. Check your property's flood zone status before designing.

Metro regional planning: Portland operates within the Metro regional government's Urban Growth Boundary (UGB). ADU construction is only permitted within the UGB — which covers Portland and surrounding incorporated cities.

Permit Process

1. Research your property on Portland Maps (portlandmaps.com) to identify zoning, overlays, and constraints
2. Contact Portland Bureau of Development Services (BDS) for a pre-application conference if needed
3. Prepare architectural plans meeting Oregon Residential Specialty Code (ORSC) requirements
4. Submit permit application through Portland's Development Hub (eDev)
5. Await building plan review (Portland aims for 2–4 weeks for complete applications)
6. Address any plan check corrections and receive permit
7. Schedule inspections at foundation, framing, and final stages

Contact: Portland Bureau of Development Services — (503) 823-7300 — portland.gov/bds

Disclaimer

ADU regulations in Portland are subject to change as Oregon continues to implement housing reform legislation. Always verify current standards directly with the Portland Bureau of Development Services and consult Oregon DLCD (Department of Land Conservation and Development) resources for statewide requirements. This page is for informational purposes only and does not constitute legal or planning advice.