Washington County planning commission weighs allowing rural accessory dwelling units

WASHINGTON COUNTY, Ore. — Washington County planning staff presented an issue paper on June 18 outlining options to allow accessory dwelling units (ADUs) in the county’s rural residential zones and asked the Planning Commission for policy guidance on how strict any future ordinance should be.

The county’s Land Use & Transportation senior planner, Todd Borkowitz, told the commission the state allows two distinct rural ADU types: a "historic dwelling ADU," which converts a qualifying historic dwelling into an ADU when a new primary dwelling is built, and a "rural ADU," which creates a new accessory unit on a lot that already contains a single detached dwelling. "The state allows 2 distinct types of ADUs," Borkowitz said as he summarized statutory limits and county implications.

County staff presented where the state’s minimum standards would permit those ADUs, and asked commissioners to weigh in on six policy questions: whether to allow one or both ADU types in rural residential districts; whether to treat the two types under the same standards (including limits on vacation rentals); whether to prohibit ADUs in groundwater-restricted areas unless served by an outside water source; whether ADUs should be barred on properties subject to nuisance orders; whether primary and accessory units must share the same water source; and whether historic dwelling ADUs should meet the same fire-protection requirements as other rural ADUs.

Why it matters: rural ADUs would create additional housing options in low-density areas without subdividing lots. State law caps rural ADUs at 900 usable square feet and limits a converted historic dwelling’s enlargement to 20% in floor area; counties may adopt stricter standards but not weaker ones. The county’s preliminary analysis identified roughly 1,562 lots that could be potentially eligible for rural ADUs and at least 237 potentially eligible lots that appear to contain a qualifying historic home, though staff said documentation of a dwelling’s construction date can be difficult for older properties.

Most commissioners expressed general support for allowing rural ADUs as a housing source, while raising implementation concerns. Commissioner K. Carlson said simply, "Yes to housing. Yes to housing. Yes to housing," urging the county to preserve existing homes where feasible. Commissioner Deborah Rosenberg said ADUs could help families "have generations on the same property," and stressed life-safety code compliance. Commissioner Mark Just said, "If the goal of ADUs in rural areas is for permanent housing needs, I don't think vacation rentals should be allowed, period." Several commissioners also asked staff to study how other Oregon counties have implemented similar rules and what enforcement mechanisms they use for short-term rental prohibitions.

Key details staff presented and commissioners discussed

- Eligibility and limits: Both rural ADU types apply only in rural residential districts (AF-10, AF-5 and RR-5) on lots of at least 2 acres, outside urban reserves, served by a fire protection provider, and not within a state-designated groundwater-restricted area (GWRA). Rural ADUs must be within 100 feet of the primary dwelling. A historic dwelling ADU is limited to a 20% floor-area increase; rural ADUs are limited to 900 square feet.

- Water and wastewater: The county’s water master flagged GWRAs, where groundwater use is restricted to mitigate over-pumping. Staff noted septic and sanitary approvals remain separate and governed by the health department; commissioners asked whether ADUs must share the same water source as the primary dwelling and generally favored flexibility when wells or topography make a shared source impractical.

- Fire protection and wildfire: State statute requires rural ADUs to be served by a fire protection provider with adequate access to firefighting equipment; county staff said some far-north and west rural areas are in Oregon Department of Forestry protection zones that do not respond to structure fires, which would effectively prohibit rural ADUs there. Commissioners emphasized life-safety code compliance and asked staff to summarize the specific fire-protection requirements they would apply.

- Vacation/short-term rentals: State statute bars rural ADUs from vacation occupancy, but the historic-dwelling provision is less explicit. Commissioners disagreed on vacation-rental policy: some favored banning short-term rentals to preserve long-term housing stock; others favored flexibility to allow occasional short-term rentals for household income or family use. Staff said the county previously drafted a short-term rental definition (30 days or fewer) but did not adopt it.

- Nuisance properties and enforcement: State law would prohibit ADUs on lots subject to certain nuisance orders. Staff and commissioners discussed how to verify nuisance status (the sheriff's office does not maintain a public chronic-nuisance list) and whether a property owner could clear a designation with documentation from law enforcement.

Process and next steps

Borkowitz said the Board of Commissioners is scheduled to consider the planning work program July 15; staff plans a 30-day public comment period after releasing a formal issue paper this summer and anticipates ordinance drafting and public hearings in the fall and winter. "We anticipate ordinance development and hearings and eventual adoption," Borkowitz said. Staff asked commissioners for direction on the six policy questions to guide ordinance development.

Formal actions at the meeting

The commission accepted the minutes of its May 21, 2025 meeting without objection.

What’s next: Staff will release the detailed issue paper for public comment, continue consultations with partner agencies (including the county water master and fire agencies), and return with draft ordinance language for public hearings later this year.