5 county-level rules, plus city-specific rules for 4 cities in Washington County, Oregon.
Verified from official government sources
Washington County stormwater is managed by Clean Water Services (CWS) under the county's Phase I MS4 permit. CWS Design & Construction Standards trigger on-site detention for projects creating 1,000 sq ft of new impervious. Post-construction facilities are owner-maintained.
Erosion control in Washington County follows Clean Water Services' Erosion Prevention and Sediment Control Manual and DEQ's 1200-C permit. Ground disturbance of 1+ acre triggers state NPDES permit; smaller projects use CWS BMPs including silt fencing and construction entrances.
Washington County is entirely inland in the Portland metropolitan area. Oregon Coastal Zone Management Act and LCDC Goals 17/18 do not apply. The nearest coastline is ~60 miles west at Cannon Beach and Tillamook County. No coastal development rules apply within the county.
Washington County participates in the FEMA National Flood Insurance Program. FEMA flood maps were last updated countywide in 2016. The Tualatin River, Fanno Creek, and numerous tributaries create significant floodplain areas. The county processes CLOMRs for projects changing flood areas.
Washington County requires grading permits for earthwork over 50 cubic yards or on slopes over 15%. Drainage cannot be diverted onto adjacent properties. Clean Water Services rules and Oregon Plumbing Specialty Code (OAR 918-750) apply to drainage systems.
4 cities in Washington County have their own environmental rules rules. Each link goes to that city's dedicated page with code citations.
See every category we cover for Washington County — parking, noise, fences, fires, animals, pools, and more.
Washington County Ordinance Hub →