ADU Rules in Corvallis, Oregon

Corvallis, the seat of Benton County, is a college town of roughly 60,000 residents on the Willamette River, home to Oregon State University (OSU). Known for its progressive, educated community and high quality of life, Corvallis is surrounded by prime Willamette Valley agricultural land — a defining feature of Oregon's statewide land use planning system. Corvallis's Urban Growth Boundary reflects Oregon's commitment to farmland protection while meeting housing needs within city limits. ADU construction in Corvallis follows the Land Development Code alongside Oregon's landmark housing reform laws.

Oregon Statewide ADU Law — Critical Context

Two Oregon laws are foundational for ADU development in Corvallis:

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. Corvallis must comply, ending single-family-only zoning. This is a significant shift for a city with extensive established single-family neighborhoods.

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 Corvallis Allows

Under the Corvallis Land 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 dedicated entrance.
• Attached ADU: An addition to the primary dwelling with a separate entrance and self-contained living facilities.
• Interior Conversion: Converting existing habitable space — basement, attic, or 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.

One ADU per single-family lot is permitted by right. Corvallis's updated code may allow additional units under HB 2001 on eligible lots.

Size and Setback Standards

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

• Rear setback: 5 feet minimum
• Side setback: 5 feet minimum
• Height: Generally 15–18 feet maximum for detached ADUs

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

Urban Growth Boundary and Farmland Context

Corvallis's UGB is tightly managed in coordination with Benton County and Oregon DLCD. The city is surrounded by some of the most productive agricultural land in Oregon — Willamette Valley soils used for grass seed, vegetables, and other crops are protected by Exclusive Farm Use (EFU) zoning under Oregon's statewide land use planning system (Goal 3 — Agricultural Lands).

ADU permits are issued only within Corvallis city limits and the UGB. Properties in Benton County outside the UGB are subject to county EFU or other rural zoning that typically does not permit residential ADUs. The UGB boundary is not the city limit in all areas — confirm your property is within the city before applying.

Willamette River and Flood Considerations

Corvallis sits on the Willamette River and some properties, particularly in low-lying areas near the river, are in FEMA-designated flood hazard zones. ADU construction in flood zones requires:

• Elevated foundations at or above the Base Flood Elevation
• Flood-resistant construction materials
• Floodplain management permits where applicable

Verify your property's flood zone designation through FEMA's Flood Map Service Center or the Corvallis Planning Division.

Seismic Considerations

Corvallis, in the Willamette Valley, faces moderate to high seismic hazard from the Cascadia Subduction Zone. Oregon DOGAMI maps liquefaction potential for Willamette Valley lowland soils. New ADU construction must meet Oregon's seismic building code standards. OSU and DOGAMI produce seismic hazard research — Corvallis has some of the best academic resources on this topic in the state.

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 Corvallis Planning Division — (541) 766-6908 — corvallisoregon.gov/planning

Disclaimer

ADU regulations in Corvallis are subject to change as Oregon continues to implement housing reform legislation. Always verify current requirements directly with the City of Corvallis Planning Division and Building Division. This page is for informational purposes only and does not constitute legal or planning advice.