Freeboard

Freeboard is elevation margin: the vertical distance between a structure's reference level and the base flood elevation. As a construction mandate, it is the extra height above the BFE that flood-zone building standards require — a designed safety cushion against the model's uncertainty. As a diagnostic on existing buildings, it is the signed gradient that separates neighbors: positive freeboard puts the modeled flood below the reference level, negative puts the structure's ground under the modeled water surface.

Freeboard converts flood analysis from zone membership to expected depth, which is where losses actually live. It is also insurance arithmetic: elevation relative to the BFE is a first-order input to premium, documented precisely by an elevation certificate.