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

In the unincorporated county, the zoning question dominates everything downstream. Exclusive farm use and forest zones carry state-mandated protections: new dwellings must satisfy the applicable farm-dwelling tests, non-farm uses need conditional or special approvals with findings, and partitions of resource land face minimum lot sizes measured in tens of acres. The county's land use planners administer these rules under Oregon's statewide planning goals, and their decisions can be appealed to the state land use board — a level of process most building-permit applicants never encounter. The floodplain overlay compounds the zoning: along the Sandy River, the Columbia, and the sloughs, elevation standards, flood-resistant construction, and floodway restrictions apply on top of the base zoning. On Sauvie Island, the drainage district's levee system adds an infrastructure partner — building near levees and pump stations means coordinating with the district that maintains them. The engineering team maps every overlay — zoning, floodplain, landslide hazard, drainage district — before the first site sketch, because each one can veto a footprint the others allow.

Rural parcels run on wells and septic, with the county's environmental health program reviewing on-site systems — soil evaluation, sizing, and reserve areas on ground that must also accommodate the building, the stormwater facilities, and the required setbacks. On small rural lots with floodplain or stream buffers, fitting all of this together is the central site-planning puzzle, and it is solved on paper before it is solved with a backhoe. Stormwater design protects the county's sensitive receiving waters — treatment for water quality is non-negotiable where runoff reaches the Sandy, the sloughs, or the Columbia. In the Gorge corridor around Corbett, landslide hazards on the bluffs and wildfire risk in the forested slopes add geotechnical and defensible-space dimensions. Seismic design for the Portland Hills fault and Cascadia governs the structural work throughout the county. The county approves what the county's codes allow — a design imported from a Portland or Gresham project will need re-engineering for county land use law, not just a new title block.