Honolulu County, HI Environmental Rules: Flood Elevation Requirements (2026)
Key Facts
- Applies to
- Zones AE and AH, flood fringe
- Residential floor
- At or above base flood elevation
- Nonresidential option
- Floodproof and watertight below BFE
- Administering agency
- Dept. of Planning and Permitting
Summary
In Oahu's flood fringe zones AE and AH, new residential construction and substantial improvements must have the lowest floor, including basements, elevated to or above the base flood elevation.
All new construction or substantial improvements of residential structures shall have the lowest floor, including basements, elevated to or above the base flood elevation.
(2) All new construction or substantial improvements of nonresidential structures shall have the lowest floor elevated to or above the base flood elevation; or together with attendant utility and sanitary facilities, be designed and constructed so that below the base flood elevation, the structure is watertight with walls substantially impermeable to the passage of water and with structural components having the capability of resisting hydrostatic and hydrodynamic loads and effects of buoyancy due to the base flood.
(3) Within zone AH, adequate drainage paths shall be provided around structures on slopes to guide floodwaters around and away from proposed structures.
(b) In areas of shallow flooding designated on the flood maps as zone AO.
(1) All new construction or substantial improvements of residential structures shall have the lowest floor, including basements, elevated above the highest adjacent grade at least as high as the depth number specified on the flood maps.
(2) All new construction or substantial improvements of nonresidential structures shall have the lowest floor elevated above the highest adjacent grade at least as high as the depth number specified on the flood maps; or together with attendant utility and sanitary facilities, be designed and
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: 2026 S-10: Supplement 10, 12-2025 Ordinance No. 25-40 through Ordinance No. 25-56).
Full Breakdown
ROH § 21A-1.8 governs the flood fringe area of Honolulu's special flood hazard zones. For property mapped as zone AE or AH, all new construction or substantial improvements of residential structures must have the lowest floor, including basements, elevated to or above the base flood elevation shown on the county's flood maps. Nonresidential structures have the same elevation option or must be floodproofed and watertight below that elevation instead. Within zone AH, developments must also provide drainage paths to route floodwater around and away from structures on slopes. The Department of Planning and Permitting administers these standards under Chapter 21A.
Violations & Fines
Building below the required base flood elevation in a flood fringe zone without an approved floodproofing alternative violates ROH Chapter 21A and can block permit issuance or final approval.
Frequently Asked Questions
How high above flood level must a new Oahu home be built?
Can a nonresidential building on Oahu be built below base flood elevation?
Sources & Official References
Other rules in Honolulu County
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