Washington County requires a building permit for retaining walls over 4 feet tall measured from the bottom of foundation to top of wall (CDC 419-4). Walls supporting surcharge loads or taller than 4 feet require engineered plans stamped by a licensed Oregon PE.
Per Washington County Building Services Guide BSE-5 and CDC 419-4, a retaining wall 4 feet or less in height (bottom of footing to top of wall) with level backfill and no surcharge does not require a building permit. Walls over 4 feet, walls supporting a driveway/structure/slope (surcharge), and tiered walls acting as a single system require a building permit and typically engineered plans stamped by an Oregon-licensed Professional Engineer. Drainage behind the wall must be addressed to prevent hydrostatic pressure. Setbacks apply near property lines and rights-of-way. In steep slope areas (hazard mapped) geotechnical review may be required. Hillsboro, Beaverton, and Tigard enforce the same 4-foot threshold from the Oregon Residential Specialty Code Section R404.4.
Unpermitted wall over 4 feet: stop-work order, retroactive engineering required, possible removal. Investigation fees typically 2x regular permit fee. Drainage failure causing damage: civil liability.
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