Washington County, OR Environmental Rules: Grading & Drainage (2026)

Grading regulation in Washington County is governed by the CDC §410 (Grading) and Oregon Specialty Codes administered by the county Building Services Division for unincorporated areas. Grading permits are required when earthwork exceeds 50 cubic yards cut-and-fill or when grading occurs on slopes over 15%, regardless of volume — this threshold captures most Bull Mountain, Cooper Mountain, and Chehalem Mountain hillside work. Plans must show existing and proposed contours, drainage patterns, erosion control, and retaining walls. Oregon common law and ORS 105.690 (Surface Waters) require that a property owner not redirect surface drainage in a way that injures adjoining property — increased concentrated flow onto a neighbor's land is actionable. Drainage swales, French drains, catch basins, and storm drain connections must be engineered per CWS Design & Construction Standards and Oregon Plumbing Specialty Code (OAR 918-750). Retaining walls over 4 feet in height (from bottom of footing to top of wall) require engineering and separate building permits under Oregon Residential Specialty Code R404. Compaction testing typically required for structural fill. Final grade must match approved plans; as-built surveys often needed for subdivisions. Cities within the county (Beaverton, Hillsboro, Tigard, Tualatin, Sherwood) have similar thresholds often aligned with the county.