Multnomah County, OR Environmental Rules: Flood Zones (2026)
FEMA flood zone rules in Multnomah County, OR, also called floodplain regulations or special flood hazard area (SFHA) rules, determine flood insurance requirements and elevation standards for new construction.
Key Facts
- Permit
- Floodplain Development Permit required, no variances
- Elevation
- Lowest floor 1 ft above base flood
- Manufactured homes
- Finished floor 18 in above base flood
- Bond
- $1,000 performance bond before permit
- Floodway
- New manufactured dwellings prohibited
Summary
Unincorporated Multnomah County requires a Floodplain Development Permit before any construction, grading, or fill in FEMA-mapped special flood hazard areas, and variances from the standards are not allowed.
No structure, dwelling or manufactured dwelling shall be erected, located, altered, improved, repaired or enlarged and no other new development including but not limited to grading, mining, excavation and filling (see “Development” under MCC 39.5005) shall occur in areas of special flood hazard unless a Floodplain Development Permit specifically authorizing the proposal has been obtained from Multnomah County. Variances to the Flood Hazard regulations are not allowed.
(1) Improvements to a structure, dwelling or manufactured dwelling or other development, which do not meet the definition of “Development” under MCC 39.5005, are exempted from obtaining a Floodplain Development Permit.
(B) Alterations, modifications or relocations to any watercourse as defined in MCC 39.5005 are subject to a Floodplain Development permit and the Watercourse Relocation and Alteration standards of MCC 39.5045.
Full Breakdown
Multnomah County Code § 39.5030 sets construction standards for the mapped flood hazard area: new and substantially improved residential structures must have their lowest floor elevated at least one foot above the base flood elevation, and manufactured dwellings need the finished floor 18 inches above it. Applicants post a $1,000 performance bond before a permit issues, released once a certified finished-construction elevation survey is filed with Land Use Planning. Section 39.5035 bars new manufactured dwellings and most new fill or construction inside the mapped floodway outright. These rules cover only unincorporated county land. Portland, Gresham, Troutdale, Fairview and Wood Village enforce their own separate floodplain codes.
Violations & Fines
Building without a Floodplain Development Permit, or below the required elevation, is a code violation that Multnomah County Land Use Planning can cite, red-tag, or block from occupancy.
Frequently Asked Questions
Does this apply to a flood-zone property in Portland?
Can I get a variance from the flood hazard standards?
Sources & Official References
Other rules in Multnomah County
Compare Multnomah County to another location·View the Oregon environmental rules overview
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