Corvallis, OR Accessory Structures: ADU Rules (2026)

Section 4.9.40 of the Corvallis Land Development Code sets the citywide standards for accessory dwelling units, or ADUs. There is no minimum lot area or width required to add one, but the property must be a legally created lot or parcel that already contains, or is actively permitted to contain, a dwelling unit. The ADU itself cannot exceed 900 square feet of floor area or 85 percent of the primary dwelling's floor area, whichever is less, and it must meet City and Building Code water, sewer, and storm drainage standards.

An ADU must otherwise meet the height, lot coverage, and Green Area standards that apply to the primary dwelling in the underlying zone, though it is not required to provide the Private Outdoor Space the primary dwelling needs. Setbacks generally track the underlying zone too, with two carve-outs: ADUs are not subject to the zone's maximum front yard setback, and a detached ADU on a Townhouse lot must keep at least a 5-foot interior side yard setback regardless of what the underlying zone otherwise requires, while still meeting the zone's exterior side yard setback.

Only one ADU is permitted per lot, parcel, or lot of record, and an ADU may never encroach into a utility easement, even where the front-yard or Townhouse side-yard exceptions would otherwise allow it. The section has been amended repeatedly since it was adopted in 2012, most recently effective June 30, 2023.