Ada County, ID Environmental Rules: Flood Elevation Requirements (2026)

Section 8-2-28(F) defines "Freeboard" as "a factor of safety usually expressed in feet above a flood level" and fixes it at exactly two feet for Ada County, so the Base Flood Elevation (BFE) plus the freeboard produces the county's Flood Protection Elevation (FPE). Section 8-2-28(G)(5)(b) turns that definition into a hard construction standard: once the BFE is determined for a site, a residential structure's application must include a FEMA-approved Elevation Certificate showing the lowest floor, including any basement or crawlspace, sits two feet above the BFE, and new residential construction in the floodway itself is prohibited outright rather than merely elevated.

Non-residential buildings face the same two-foot-above-BFE elevation standard but may substitute a Floodproofing Certificate showing the structure is floodproofed to that same two-foot mark instead of being physically raised. The same two-foot freeboard threshold extends to swimming pools, which need an Elevation or Floodproofing Certificate showing protection two feet above BFE; to new bridges, whose horizontal supports must clear the BFE by two feet; and to new subdivision roads, which must be elevated two feet above the base flood elevation while still allowing floodwater to pass beneath so the road does not act as a check dam.

When no BFE has yet been established for a site, the Floodplain Administrator is directed to obtain and reasonably use whatever BFE and floodway data is available from a federal, state or other engineering source before applying the two-foot standard.