Portland, OR Environmental Rules: Flood Elevation Requirements (2026)
Key Facts
- Freeboard, Willamette River
- base flood elevation + 2 ft
- Freeboard, Columbia River
- base flood elevation + 1 ft
- Lowest floor rule
- must clear flood protection elevation
- Administered by
- Portland Permitting & Development
Summary
Portland requires new construction in flood hazard areas to elevate the lowest floor above the base flood elevation plus a freeboard buffer that runs 1 to 2 feet depending on the waterway.
Willamette River FIRM Flood Zone AE. These flood zones represent areas for which the base flood elevations are determined. The flood protection elevation is the base flood elevation plus 2 feet of freeboard.
E. Johnson Creek, Fanno Creek and Crystal Springs Creek FIRM Flood Zone AE. This flood zone represents areas for which the base flood elevations are determined. The flood protection elevation is the base flood elevation plus 2 feet of freeboard.
F. Johnson Creek FIRM Flood Zone AH. This flood zone represents areas of shallow flooding depth (1 to 3 feet) for which base flood elevations are determined. The flood protection elevation is the base flood elevation plus 2 feet of freeboard.
G. Johnson Creek FIRM Flood Zone AO. This flood zone represents areas of shallow flooding depth (1 to 3 feet) for which the depths of flooding are determined. The base flood elevation is the ground surface elevation plus the depth of flooding as shown on the FIRM map. The base flood elevation for a structure is the highest grade adjacent to the structure plus the depth of flooding as shown on the FIRM map. The flood protection elevation is the base flood elevation plus 2 feet of freeboard.
Full Breakdown
Portland City Code Chapter 24.50 sets the flood protection elevation for every permit issued in a mapped flood hazard area: the base flood elevation (the 100-year flood height) plus a freeboard cushion. On the Willamette River, Johnson Creek, Fanno Creek, Tryon Creek, and Crystal Springs Creek floodplains that cushion is 2 feet; on the Columbia River and the Multnomah, Peninsula No. 1, and Peninsula No. 2 drainage districts it's 1 foot. New or substantially improved residential structures must have their lowest floor, including any basement, built at or above that elevation, verified by a FEMA elevation certificate before Portland Permitting & Development signs off.
Violations & Fines
Building below the required flood protection elevation blocks permit sign-off on the FEMA elevation certificate. Encroaching into the mapped floodway is prohibited outright under § 24.50.060(D) unless a registered engineer certifies no increase in the base flood elevation.
Frequently Asked Questions
How much freeboard does Portland require above base flood elevation?
Who administers Portland's flood hazard rules?
Sources & Official References
Other rules in Portland
Compare Portland to another location·View the Oregon environmental rules overview
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Flood Elevation Requirements in Nearby Cities
How other cities in Multnomah County handle flood elevation requirements.