Corvallis, OR Environmental Rules: Flood Elevation Requirements (2026)

Corvallis defines Design Flood Elevation (DFE) in Land Development Code Section 1.6.40 as one foot above Base Flood Elevation (BFE), the one-foot freeboard that Section 4.5.110.04 then makes mandatory for residential construction: new construction, conversion, and Substantial Improvement of any residential structure, including mobile and Manufactured Dwellings, must have the Lowest Floor, defined to include basements, habitable attached garages, and mechanical and electrical equipment, elevated at or above the DFE. In an AO Federal Flood Zone, where FEMA maps a flood depth rather than an elevation, the Lowest Floor instead must clear the mapped flood Depth Number by at least one foot, or, if the Depth Number is unknown, clear the Highest Adjacent Grade by at least three feet.

Crawl spaces and other enclosed areas below the Lowest Floor need flood openings sized to at least one square inch of net vented area per square foot of enclosed space, with a minimum of two openings on two sides and the bottom of each opening no higher than one foot above grade, under Section 4.5.110.04.b. Nonresidential buildings get an alternative under Section 4.5.110.08: flood-proofing the Lowest Floor watertight to the DFE, certified by a registered engineer or architect, instead of elevating it. Critical Facilities, defined in Section 1.6.40 to include fire and police stations and emergency-preparedness centers, must clear an even higher bar under Section 4.5.110.11, with the Lowest Floor elevated three feet above Base Flood Elevation rather than the standard one-foot freeboard.