Lane County, OR Environmental Rules: Flood Elevation Requirements (2026)

271 defines "Base Flood Elevation (BFE)" as the elevation to which floodwater is anticipated to rise during the base flood, the flood with a one percent annual chance of occurring. Within riverine Special Flood Hazard Areas that have BFE data (Zones A1-A30, AH, and AE), the code's residential construction standard, section (5)(b)(iii)(bb)(A), requires the lowest floor of any new or substantially improved residential structure, including a basement, to be elevated at or above two feet above the BFE, or three feet above the highest adjacent grade where no BFE has been established.

Nonresidential structures face the identical two/three-foot standard under section (5)(b)(iii)(cc), unless the owner instead flood proofs the building watertight below the base flood level and certifies the design through a registered engineer or architect. Manufactured dwellings must have the bottom of the longitudinal chassis frame beam set at the same two-foot (or three-foot) elevation, with electrical crossover connections kept at least 24 inches above BFE. A transition clause in section (5)(a)(xii) held the freeboard at one foot above BFE (two feet above grade without BFE data) until September 7, 2023, after which the two-foot standard now in force took effect.

Enclosed areas below the lowest floor, such as crawlspaces or garages, must carry flood openings sized to at least one square inch per square foot of enclosed area, with the lowest opening no higher than one foot above grade. A floodplain development permit from the Planning Director, who serves as Floodplain Administrator, is required before any such construction begins, and an Elevation Certificate documenting the as-built lowest-floor elevation must be filed before the final inspection.