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

Portland City Code Title 24 (Building Regulations) and PCC 24.70 (Excavation and Grading) require a grading permit for any excavation or fill exceeding 50 cubic yards, modifications to natural drainage courses, or work on slopes over 20%. Portland's West Hills (Southwest and Northwest neighborhoods) are mapped as Landslide Hazard Areas in Portland's Environmental Overlay Zones, requiring geotechnical engineering reports for most ground disturbance. ORS 105.170 and common law adopt the Reasonable Use Doctrine - drainage cannot be concentrated and discharged onto a neighboring property so as to cause damage. Retaining walls over 4 feet (measured from bottom of footing) require a separate engineered structural permit (ORSC R404). Compaction testing required for structural fill. Final grade must match approved drainage plans before certificate of occupancy. Gresham Development Code 8.60 and Troutdale TMC 17.80 have similar thresholds. Unincorporated Multnomah County MCC 39 requires grading permits on Significant Environmental Concern (SEC) overlays (streams, wetlands, steep slopes, Columbia Gorge boundary) and any fill exceeding 50 cubic yards. Sandy River Conservation Area and Columbia Slough have additional protections. Oregon DSL (Department of State Lands) removal-fill permits apply within wetlands or waters of the state, with thresholds as low as 50 cubic yards in Essential Salmon Habitat.