ADU Rules in Tigard, Oregon

Tigard is a Washington County city of approximately 55,000 residents, a diverse Portland suburb known for Washington Square mall and its position along the Fanno Creek Greenway. Tigard has been active in updating its land use regulations in response to Oregon's housing reform mandates. ADU construction in Tigard is governed by the Tigard Development Code alongside Oregon's landmark statewide housing laws, with notable environmental considerations from Fanno Creek and its associated greenway.

Oregon Statewide ADU Law — Critical Context

Two Oregon laws are foundational for ADU rights in Tigard:

Oregon HB 2001 (2019) requires cities with populations over 10,000 to allow middle housing — duplexes, triplexes, fourplexes, and cottage clusters — in all residential zones. Tigard must comply, ending single-family-only zoning and requiring the city to update its Development Code to permit a range of housing types in residential districts.

Oregon's statewide ADU framework is SB 1051 (2017) plus HB 2001 (2019) middle housing. HB 2098 (2021) is a rental-assistance bill, not ADU.

What Tigard Allows

Under the Tigard Development Code and state mandate, the following ADU types are permitted in residential zones:

• Detached ADU: A freestanding structure on the same lot as the primary home, with its own kitchen, bathroom, and entrance.
• Attached ADU: An addition to the primary dwelling with a dedicated separate entrance and self-contained living facilities.
• Interior Conversion: Converting existing habitable space — basement, attic, or interior rooms — within the primary structure into a separate dwelling unit.
• Garage Conversion: Converting an existing detached or attached garage into habitable ADU space meeting Oregon building code standards for habitability.

One ADU per single-family lot is permitted by right. Tigard's updated code following HB 2001 may allow greater density through middle housing provisions on eligible lots.

Size and Setback Standards

Oregon law prohibits Tigard from requiring ADUs smaller than 900 square feet or 75% of the primary dwelling's floor area, whichever is less. Standard setbacks for detached ADUs in Tigard low-density residential zones typically include:

• Rear setback: 5 feet minimum
• Side setback: 5 feet minimum
• Height: Generally 15–20 feet maximum for detached ADUs

Legal nonconforming structures being converted to ADUs may maintain existing setbacks even if they do not meet current new-construction standards.

Fanno Creek and Clean Water Services (CWS) Constraints

Fanno Creek and its tributaries run through Tigard, and the Fanno Creek Greenway is a significant natural resource corridor. Properties near Fanno Creek or other waterways may be subject to:

• Clean Water Services (CWS) vegetated corridor buffers: CWS is the regional stormwater agency for Washington County. Vegetated corridor setbacks (typically 50–200 feet from stream centerline depending on stream size and condition) restrict construction near natural drainage features. A CWS Site Assessment is required for development near vegetated corridors.
• FEMA flood zone requirements: Properties in the Fanno Creek floodplain must comply with floodplain management standards, including elevated foundations and flood-resistant construction.

Always check your property's proximity to vegetated corridors and flood zones before finalizing ADU placement.

Metro Regional Government and Urban Growth Boundary

Tigard is within the Metro regional government's UGB for the Portland metro area. ADU development is permitted only within Tigard city limits and the Metro UGB. Washington County properties outside the UGB are subject to rural land use regulations that do not permit ADUs on most parcels.

Seismic Considerations

Tigard, in the Tualatin Valley portion of the Portland metro area, faces seismic hazard from the Cascadia Subduction Zone. DOGAMI maps significant liquefaction potential in Tualatin Valley lowland areas, which include parts of Tigard. New ADU construction must meet Oregon's seismic building code standards.

Permit Process

Oregon's statewide ADU framework is SB 1051 (2017) plus HB 2001 (2019) middle housing. HB 2098 (2021) is a rental-assistance bill, not ADU.

Contact: City of Tigard Community Development — (503) 718-2421 — tigard-or.gov

Disclaimer

ADU regulations in Tigard are subject to change. Always verify current requirements with the City of Tigard Community Development Department and Clean Water Services. This page is for informational purposes only and does not constitute legal or planning advice.