Lyon County, NV Environmental Rules: Flood Elevation Requirements (2026)

Under section 15.800.12(C)(5)(a), new construction and substantial improvements must have the lowest floor, including any basement, elevated to create freeboard above the base flood elevation, with the exact amount set by zone. In Zone AO, the lowest floor must clear the FIRM depth number by at least 1.5 feet, or reach 3.5 feet above the highest adjacent grade if no depth number is shown; in Zone A the floor must sit at least 1.5 feet above the base flood elevation as determined by a Nevada-licensed engineer or surveyor and approved by the Floodplain Administrator; in any other special flood hazard area with a determined base flood elevation, the same 1.5-foot minimum applies.

In the X-shaded flood zone, the floor must clear the pre-developed adjacent grade by 1.5 feet or the applicant must provide an engineered drainage plan diverting water around the structure. On alluvial fan floodplains identified in the Area Drainage Master Plans, the standard rises to a minimum of two feet above the base flood elevation to account for sedimentation. Manufactured homes placed, substantially improved, or substantially damaged by flood in a special flood hazard area must be elevated on a permanent foundation at least 1.5 feet above the base flood elevation and securely anchored.

Nonresidential structures may instead be flood proofed watertight, certified by a Nevada-licensed engineer or architect. Upon completion, a Nevada-licensed engineer or land surveyor must certify the lowest floor elevation, verified by the county building inspector and recorded on the current FEMA Elevation Certificate before the Floodplain Administrator accepts compliance.