Kauai County, HI Fence Regulations: Retaining Walls (2026)

Section 105.2, item 4, exempts retaining walls not over 4 feet in height, measured from finish grade to the top of the wall, from needing a building permit, provided they are built to the Comprehensive Zoning Ordinance, Floodplain Management, and Traffic Code chapters. Rip-rap retaining walls get a slightly different measure: they are exempt at a slope of not less than 1:1 with a vertical dimension not over 4 feet. Once a retaining wall exceeds those 4-foot thresholds, it needs a building permit under Section 105.1, and Section 107.1 adds an engineering requirement that kicks in at a lower height than the permit exemption itself: any retaining wall design for a wall 5 feet or more in height must be prepared, designed, approved, and stamped by a duly registered, licensed architect or engineer in the structural or civil branch before the Building Division will accept the submittal.

That stamped-plan requirement sits within the same Section 107.1 that requires construction documents generally to be prepared by a registered design professional when the work affects public safety or health, so a taller retaining wall cannot rely on an unstamped, owner-drawn plan even if a similar wall under 4 feet could go up without any plan review at all. Walls in the 4-to-5-foot range need the permit but not necessarily the professional stamp, since the stamp threshold in Section 107.1 is specifically set at 5 feet.