ADU rules in Kaua’i

Kaua'i County Code Sec. 8-15.2(a) lets any residentially zoned lot on which only one single-family residential dwelling is permitted add "one (1) additional single-family residential dwelling unit (attached or detached)", so a detached backyard Additional Dwelling Unit (ADU) is allowed across the R-1 through R-20 districts without a hearing. The ADU is a full second single-family dwelling, not a size-capped accessory unit. Separately, Sec. 8-1.4(i) authorizes one guest house (a building of no more than 800 square feet that may contain a kitchen) per dwelling unit in R-1 to R-6, R-10 to R-20, CN, CG, AG, O and UNV, which is how most Kaua'i owners add a second detached rental structure today. Do not conflate either with the Additional Rental Unit (ARU): the ARU standards in Article 30, Sec. 8-30.1(a) through (f), carried a five-year sunset from Ord. No. 1026 of 3-19-2018, expired 3-19-2023, and now read "(Reserved)" in the published Code. On lots that are not residentially zoned, Sec. 8-15.1(a) ADUs were repealed effective 12-31-2006 and only a closed grandfather path survives.

The same sentence of Sec. 8-15.2(a) covers attached and internal units, permitting the additional dwelling "(attached or detached)". Sec. 8-1.5 confirms the scope, defining an "Additional dwelling unit (ADU)" as "a structure or portion thereof designed and used for single-family residential purposes as permitted under Article 15 of this Chapter, and which can be detached from or attached to an existing residence, to be used for single-family occupancy and containing one kitchen", so a basement, wing or internal conversion with a single kitchen qualifies. The lapsed ARU could also be attached or internal, but the Sec. 8-1.5 ARU definition warned that "When built within an existing residential dwelling unit or attached to one, the two units together shall constitute a multi-family dwelling". A guest house cannot be an internal conversion: Sec. 8-1.5 defines it as "a building" of no more than 800 square feet, and Sec. 8-1.4(i)(3) requires its own dedicated off-street stall.

Article 15 sets no floor-area ceiling for an additional dwelling unit. Sec. 8-15.2(a)(1) instead requires that "All applicable County requirements, not inconsistent with Section 46-4(c), Hawai'i Revised Statutes and the County's zoning provisions applicable to residential use are met, including, but not limited to, building height, setback, maximum lot coverage, parking, and floor area requirements", so the real constraints are Sec. 8-4.3(d)(3) land coverage (buildings plus pavement not exceeding 60 percent of the lot in R-1 to R-6, 80 percent in R-10 and 90 percent in R-20), Sec. 8-4.5(b)(1) height (no more than two stories above and one below the finished grade at the main entry, 20 feet to the highest exterior wall plate and 30 feet to the highest point of the roof), and Sec. 8-4.3(b) setbacks (10 feet front, and 5 feet or half the height of the nearest wall, whichever is greater, at the side and rear). A guest house is capped by definition at 800 square feet (Sec. 8-1.5). The ARU had a harder cap while it ran: former Sec. 8-30.1(a)(1) set "The maximum total floor area for an Additional Rental Unit shall be 800 square feet", measured from the interior faces of exterior walls and including enclosed attached garages or storage but excluding breezeways, lanais and porches, and former Sec. 8-30.1(a)(6) granted an extra 10 percent of land coverage beyond the Sec. 8-4.3 maximum for the ARU and its parking; both lapsed with the program.

Neither Sec. 8-15.2 nor Article 15 generally conditions an additional dwelling unit on the owner living at the property, at application or on any ongoing basis. The guest house rules in Sec. 8-1.4(i) also impose no occupancy test, although Sec. 8-1.4(i)(4) provides that a guest house "shall never be separated in ownership from the ownership of its primary dwelling by any owner or any heir, successor, or assign of any owner, including but not limited to submitting the lot or any portion thereof to a condominium property regime (CPR)". The lapsed ARU likewise had no owner-occupancy requirement; former Sec. 8-30.1(a)(4) instead required that "The Additional Rental Unit shall be used only for long-term rental or otherwise occupied for a period of at least six months per year", and former Sec. 8-30.1(a)(3) barred CPR separation. Owner occupancy does appear in the Code, but for a different use: a "Homestay" under Sec. 8-1.5 must be an owner-occupied dwelling unit whose owner currently holds the Sec. 5A-11 homeowner's exemption for the homestay site.

Sec. 8-4.5(a)(5) applies to all residential development and states that "A minimum of two off-street parking spaces per dwelling unit shall be provided". Because an Article 15 additional dwelling unit is a dwelling unit, an ADU brings two more required stalls, which is one of the heavier ADU parking requirements in the directory. The same subsection adds that "For Guest Houses, one off-street parking space per Guest House shall be provided in addition to the required off-street parking for the primary dwelling unit", and Sec. 8-1.4(i)(3) repeats that a guest house must be "permanently provided with one (1) off-street parking space per guest house in addition to the required off-street parking for all dwelling unit(s)". The lapsed ARU was the cheap option here too: former Sec. 8-30.1(a)(2) required only "One off-street parking space per Additional Rental Unit ... in addition to the required off-street parking for the primary dwelling unit(s)". Where spaces serving more than one dwelling unit sit in a common parking area they must be paved, and paved parking areas must be set back at least five feet from public right-of-way lines.

An additional dwelling unit is reviewed administratively. Sec. 8-4.7(a) requires a Class I Zoning Permit where the parcel is outside a Constraint District and a Special Treatment District and is not large enough for more than one dwelling unit under the district density, and Sec. 8-4.7(b)(2) a Class II Permit for one dwelling unit on a parcel that could hold more; under Sec. 8-3.1(c) and (d) both are "issued with or without conditions or denied by the Planning Director" or a designee for a $30 or $60 fee, and the application "shall be deemed approved" if the Director does not act within 30 days. No public hearing and no Planning Commission vote is required for a normal ADU. Before the building permit the owner must complete an ADU Facilities Clearance Form carrying written adequacy confirmations from the Department of Public Works (public sewer), the state Department of Health (private or individual wastewater), the Department of Water and the Kaua'i Fire Department, per Sec. 8-15.2(a)(4) and (a)(5); those forms are now filed through the county's connect.kauai.gov portal. The path escalates to a Class III permit, which the Planning Director may issue provisionally but which three Planning Commissioners can pull for Commission review within 30 days, when the parcel lies in a Constraint District (drainage, flood, sea level rise, slope, soils or tsunami) or a Special Treatment District, and a separate Special Management Area approval under HRS chapter 205A and the Planning Commission's SMA rules applies along the coast.

An ADU may be rented long term, and KCC Sec. 22-28.2 (Ord. No. 1106, 3-15-2022) makes private restrictions unenforceable against it: "covenants, conditions, deed restrictions, declarations of condominium property regime, association bylaws, and any other agreements that run with the land shall not limit or prohibit Long-Term Rentals, Additional Dwelling Units, Additional Rental Units, and Guest Houses", subject to the Sec. 22-28.3 carve-outs for agreements in existence on 3-15-2022, agreements that limit ADUs inside Visitor Destination Areas, and deed restrictions imposed by the Planning Commission during subdivision. Short-term use runs the other way: Sec. 8-17.1 prohibits transient vacation rentals except as Article 17 allows and Sec. 8-17.8(a) bars single family TVRs "in all areas not designated as Visitor Destination Areas" other than National or State Register properties, so outside a VDA an ADU cannot lawfully be rented for less than 180 days; the Planning Department states it plainly, "Any short term rental of a room within a home, or a home, less than 180 days is not permitted, nor can it be applied for." A guest house is barred from transient use everywhere, inside or outside a VDA (Sec. 8-1.4(i)(5)), and the lapsed ARU carried the same bar in former Sec. 8-30.1(a)(5) plus the six-month occupancy floor in (a)(4). Article 15 imposes no condominium-property-regime or separate-sale bar on the ADU itself, unlike Sec. 8-1.4(i)(4) for guest houses and former Sec. 8-30.1(a)(3) for ARUs.