How Does Engineering Permitting Work in Unincorporated Washington County, OR?

The most important thing to understand about a Washington County project is that approval is a two-key system. The county's Land Use & Transportation department reviews land use, building code, grading, and transportation; Clean Water Services reviews stormwater management, erosion control, and sanitary sewer as the service provider. Neither defers to the other, and their standards are separate documents the design team must satisfy simultaneously. The pre-application process should include both — discovering the CWS requirements after the county permit is submitted is a classic schedule-killer. For the civil engineer, CWS standards drive the drainage design: water quality facilities sized per CWS methods, flow control addressing hydromodification in the Tualatin watershed, vegetated corridor protections with required widths and planting standards, and erosion and sediment control during construction that CWS inspects in the field. Sanitary connections, pump station requirements where gravity does not work, and system development charges are all in the CWS track. The county track handles the building, the grading permit, the transportation improvements, and the land use approvals. Staff the project for both from day one.

The vegetated corridor protections are the site-planning constraint that most often surprises suburban developers: streams and wetlands threading through Aloha, Bethany, and the other urban unincorporated areas carry protected corridors with widths, native planting requirements, and development restrictions. These corridors cannot be piped or paved over by right — the site plan works around them, and density calculations must account for the unbuildable corridor area. Wetland delineations and corridor assessments belong at due diligence. Floodplain along the Tualatin River and tributaries like Beaverton Creek and Rock Creek adds elevation standards and floodway restrictions on corridor parcels. Transportation review covers frontage improvements to county standards, access spacing on arterials, and traffic analysis for larger projects — the county builds and maintains this road network, and it collects its improvements through development. Seismic and landslide review apply on the sloped terrain at the urban fringe. The county's code rewards design teams that read it early and punishes those who assume the neighboring city's rules transfer.