The purpose of this page is to define the lowest horizontal structural member, a commonly used term in floodplain management.
In V Zones, new construction must have the elevation of the lowest horizontal structural member at or above the Base Flood Elevation (BFE). Horizontal structural members are obstructions and can transmit the force of wave impacts to rest of the structure. This elevation is used as the reference level to determine insurance rates. This contrasts with construction and insurance rating in A Zones, which uses the elevation of the lowest floor including basement as the reference level. This requirement is to keep the entire building in a V Zone above the anticipated breaking wave height of a base flood storm surge.
In an elevated building, the lowest beam, joist, or other horizontal member that supports the building is the lowest horizontal structural member. Grade beams installed to support vertical foundation members where they enter the ground are not considered lowest horizontal members.
- (e)(4) - V Zone Elevation Requirement
- Section 18.104.22.168