Kauai County, HI Accessory Structures: ADU Rules (2026)

Kaua'i County Code Sec. 8-15.2 lets an owner of a residentially zoned lot, where zoning permits only one single-family dwelling, add one additional single-family dwelling unit, attached or detached, without needing a rezoning or variance. The unit must meet every applicable County zoning requirement for building height, setback, maximum lot coverage, parking and floor area, as long as those requirements are not inconsistent with Section 46-4(c) of the Hawai'i Revised Statutes. The allowance does not apply to lots already developed under a project development or multi-family scheme where the total unit count already exceeds the density the zoning district otherwise allows, and any guest house built on the same lot is governed separately under Sec. 8-1.4(i).

A companion provision, Sec. 8-15.1, extends a similar additional dwelling unit allowance to lots that are not zoned residential, such as agricultural lots with a single farm dwelling, subject to the same building-standard requirements plus written facilities clearance from the Department of Public Works, Department of Water, Department of Health, and the Kaua'i Fire Department, using an ADU Facilities Clearance Form filed with the Building Permit application through the Building Division. That non-residential ADU allowance carried a December 31, 2006 sunset that has since closed to new applicants except through a narrow, now-lapsed re-certification window that required a $250 fee and a June 30, 2017 deadline. Sec. 8-15.2's residentially zoned version carries no such sunset. Neither section overrides a private deed restriction or covenant limiting the number of dwellings on a lot.