Hawaii County, HI Environmental Rules: Flood Elevation Requirements (2026)

Chapter 27 exists, per Section 27-3, to keep people and property out of harm's way and to hold down the public cost of flood rescue, relief, and repeated flood-control spending. Section 27-16 puts the floodplain administrator, housed in the Department of Public Works, in charge of reviewing every building permit, grading permit, and subdivision proposal in a special flood hazard area, and requires the office to keep the Flood Insurance Study, Flood Insurance Rate Maps, and every elevation and floodproofing certification on permanent file. Section 27-18(d) sets the numbers: in Zones AE and AH, new construction, improvements to repetitive-loss structures, and substantial improvements must put the lowest floor at or above the base flood elevation plus a one-foot freeboard for residential buildings, with nonresidential buildings elevated or floodproofed to the same line and, if built below it, certified watertight by a licensed engineer or architect.

Zone AO carries its own rule: elevate above the highest adjacent grade by at least one foot above the FIRM's depth number, or three feet if none is listed. Floodways are stricter still: Section 27-18(c)(1) bars any encroachment, including fill, unless a Hawai'i-licensed professional civil engineer certifies with supporting data that it will not raise the base flood elevation during a base flood discharge. Section 27-17 backs all of this with paperwork: certified building plans, an elevation certification on the plans themselves, a Special Flood Hazard Area Certification, and, before occupancy, a FEMA Elevation Certificate based on as-built construction.