Washington County, OR Accessory Structures: ADU Rental Restrictions (2026)

Washington County treats rural land differently from its in-town lots when it comes to short-term rental of accessory units. Two rural ADU categories exist under the Community Development Code: the Rural ADU (§ 430-3), available on any parcel of at least two acres outside the urban growth boundary and an urban reserve, and the Rural Historic ADU (§ 430-4), which lets an existing historic home be converted into an ADU when a new primary dwelling is built on the same lot. ' Oregon's statute defines vacation occupancy as short-term transient lodging, so the county's rule bars owners from running their rural ADU as a short-term or vacation rental, even though the county permits the unit itself through a Type I procedure with no public hearing.

The restriction sits alongside other conditions the county imposes on rural ADUs: the lot must be at least two acres, hold no more than one existing primary dwelling, and, for the standard Rural ADU, the accessory unit must sit within 100 feet of the primary dwelling; the historic-home version instead caps the converted unit at 120% of its square footage at the time of conversion. Urban ADUs inside the growth boundary carry no comparable vacation-rental ban written into the CDC itself. A lot or parcel containing a Rural ADU also cannot be subdivided so the ADU and the primary dwelling end up on separate parcels, keeping the accessory unit tied to the same ownership as the main home rather than sold or rented off separately.