ADU rules in Corvallis

Corvallis lists 'Residential - Accessory Dwelling Unit' as a permitted Building Type in every residential zone (RS-6, RS-9, RS-12, RS-20, the RMU zones and MUR) and also in the P-AO, MUE, OSU and AG-OS zones, each row cross-referencing Section 4.9.40 for the standards. Each zone chapter otherwise requires all dwelling units on a lot to sit in a single building, but carves out an express exception for one detached ADU built with a Single Detached, Duplex, Triplex, Fourplex, Townhouse or Cottage Cluster. Only one ADU is allowed per lot, parcel or lot of record, and Section 4.9.40.a states there is no minimum lot area or width required to develop an ADU. The AG-OS zone is the one narrow exception: there the ADU building type is allowed only in accordance with Section 4.3.50.a (caretaker, farm owner or operator, or kennel owner dwellings).

The LDC building-type definition is explicit that 'An Accessory Dwelling Unit may be interior to, attached to, or detached from the primary dwelling unit,' so a basement or internal conversion, an attached addition and a freestanding backyard cottage are all the same building type and all run through Section 4.9.40. The city's ADU page says the same thing in plain language and adds the practical building-code consequences: fire separation walls and ceilings between the units when the ADU is integrated into the primary building, and generally 6 feet of separation between buildings when it is freestanding. The 900 sq ft / 85 percent cap, the setback rules and the one-per-lot limit apply identically to all three forms.

Section 4.9.40.b caps an ADU at 900 square feet of floor area or 85 percent of the primary dwelling's floor area, whichever is less, so reaching the full 900 sq ft takes a primary dwelling of roughly 1,059 sq ft or more. Where a lot holds several dwelling units, the 'primary dwelling' for this calculation is the unit with the greatest floor area. There is no ADU-specific height limit; instead the ADU must meet the underlying zone's height, lot coverage and Green Area standards as they apply to the primary dwelling, which in RS-6 means 30 ft. maximum height, 60 percent maximum lot coverage and at least 40 percent of the lot retained as Green Area. Two size-related breaks apply: ADUs carry no Private Outdoor Space requirement, and inside the University Neighborhoods Overlay an ADU does not count against the maximum floor area ratio.

Section 4.9.40 sets out the complete list of ADU standards (legal lot status, size, utilities, height and lot coverage and Green Area, setbacks, one per lot, no easement encroachment) and contains no owner-occupancy condition; a full-text scan of the current Land Development Code turns up 'owner-occupied' only in the Bed and Breakfast portion of the Home Business definition, never in the ADU rules. State law independently forecloses such a requirement: ORS 197A.425(1)(b)(B) provides that 'reasonable local regulations relating to siting and design' for ADUs 'does not include owner-occupancy requirements of either the primary or accessory structure.' The statute's only carve-out, in ORS 197A.425(2), lets a city still impose owner occupancy on vacation occupancies as defined in ORS 90.100, and Corvallis has adopted no such ADU rule.

Corvallis repealed its off-street vehicle parking minimums outright. LDC Section 4.1.20.a now reads that 'The provision of a minimum number of off-street parking spaces for vehicles is not a requirement of this Code,' a change made by Ordinance 2023-19 (adopted at the June 5, 2023 City Council hearing on the city's Climate-Friendly and Equitable Communities parking package, effective June 30, 2023). The same ordinance deleted the older ADU-specific subsection 4.9.40.f that had said additional off-street parking was not required for an ADU, because the citywide repeal made it redundant. Parking you choose to build still has to meet the design, driveway, access and vision-clearance standards of Chapter 4.1, and bicycle parking minimums do survive for larger multi-dwelling development. ORS 197A.425(1)(b)(B) separately bars the city from requiring additional off-street parking as a condition of ADU approval.

An ADU meeting Section 4.9.40 is a building permit, not a land use application. The city's Development Services page states that 'ADUs are permitted outright on most residential properties, subject to the development standards of Corvallis Land Development Code (LDC) Section 4.9.40' and that 'An ADU complying with the standards of LDC Section 4.9.40 can be developed through the building permit process.' The zone chapters agree: ADU appears in each zone's Permitted Building Types table with no Conditional Development marker, and Plan Compatibility Review under Chapter 2.13 is triggered only for uses a zone specifically flags for it. Applications are filed through the city's online permit portal at corvallispermits.com. Discretionary review enters only on the margins: a Historic Preservation Permit if the property is a designated historic resource or sits in the Historic Preservation Overlay, or a Development Standards Adjustment under Chapter 2.12 if the applicant needs relief from a dimensional standard.

Nothing in Section 4.9.40 restricts who may occupy an ADU, so it can be rented long term like any other dwelling unit. Registration is required though: Corvallis Municipal Code Section 8.03.300.065 makes owners of residential rental units register them with the City before allowing occupancy by a tenant and pay an annual Rental Housing Program fee per unit (posted by the city at $17 per unit for 2026, escalating $1 in odd-numbered fiscal years), with civil penalties for failing to register or pay; rentals are also subject to the Corvallis Livability Code in CMC Chapter 9.02. Short-term renting is the constrained side. LDC Section 3.0.30.01 defines Residential Use Types as occupancy of living accommodations 'on a wholly or primarily non-transient basis,' while 'Lodging Services' (provision of temporary overnight accommodations) is a Commercial Use Type, and the RS-6 and RS-9 use tables permit no Lodging Services at all; Bed and Breakfast Facilities are permitted only in RS-12, RS-20 and commercial or mixed use zones. Renting up to two bedrooms inside an owner-occupied dwelling is instead classed as a Home Business, an accessory use allowed in the residential zones. Any stay under 30 days also triggers the city's 9 percent lodging tax and a Lodging Tax Registration Form, collected by the Oregon Department of Revenue since February 1, 2022.