Building an ADU (Accessory Dwelling Unit) in Honolulu County, Hawaii can have several benefits, both to homeowners and the community. If you’re a homeowner with a lot over 5,000 square feet and your property meets the minimum requirements of Honolulu City Council Bill 20, you can build a separate living unit, either attached to your home or detached, up to 800 square feet. If your lot is between 3,500 to 4,999, the ADU can be up to 400 square feet, while a lot less than 3,500 is not eligible for an ADU. The ordinance also states that as an alternative to building an entirely new structure, it is possible to partition an already standing structure into both a primary and accessory dwelling.
This ordinance passed in 2015 with the intention of adding additional affordable rental units to Oahu, while maintaining the character of neighborhoods. In theory, if hundreds or even thousands of ADUs are built, the increased supply of rental units should help alleviate some of the housing shortage and reduce upward pressure on rental prices. This proposed solution to the short supply of housing was chosen to try to avoid leveling neighborhoods to make way for condos and apartment units, while also creating additional income sources for homeowners.
The ADU ordinance also helps address a gray-area rental market that rose up in the years following the 1990 “Housing-Ohana dwellings” Ordinance of Honolulu. This previous bill stated that “one ohana dwelling unit may be located on a lot zoned for residential, country, or agricultural use, with the following limitations:… The ohana dwelling unit shall be occupied by persons who are related by blood, marriage or adoption to the family residing in the first dwelling. Notwithstanding this provision, ohana dwelling units for which a building permit was obtained before September 10, 1992 are not subject to this restriction and their occupancy by persons other than family members is permitted.” The ADU ordinance allows for this second dwelling unit to be rented to non-related parties. However, language in Bill 20 emphasizes that the primary unit on the lot should be occupied by the property owner, owner’s family, or a designated authorized representative, which the bill clarifies “For purposes of this section, ‘designated authorized representative(s)’ means the person or persons designated by the property owner or owners to the department of planning and permitting, who are responsible for managing the property.” In addition, the bill states that if either primary dwelling or the accessory dwelling is rented out, they must be for long term rentals (At least a 6 month long initial lease which can be followed by month-to-month for an existing tenant) and not bed & breakfast or transient vacation rentals.
In order to apply for an ADU, “the applicant shall first obtain written confirmation from the responsible agencies that wastewater treatment and disposal, water supply, and access roadways are adequate to accommodate the accessory dwelling unit.”
Bill 20 goes further to detail the path for previously built structures to become ADUs:
“An existing, legally established, accessory structure constructed prior to the effective date of this ordinance in the country or residential district may be converted to an accessory dwelling unit and allowed to exceed the maximum floor area established by Section 21-5. and/or be exempted from the off-street parking requirement established by Section 21- 5. (c)(4) and contained in Table 21-6.1 subject to the following conditions: Provided the director finds that viable constraints do not allow the reduction of the floor area of the existing accessory structure. Provided that the director finds that no feasible alternative off-street parking site exists due to the placement of structures on, and/or the topography of, the zoning lot.”
The most important limitations of the bill are that homeowners must have a lot at least 3,500 square feet large, not in a planned community, or part of an association, and the separate living area must include a kitchen, bathroom, and bedroom, have a parking space, and appropriate water and wastewater access.
Eight Hundred square feet is enough to build a comfortable two bedroom rental and even if construction of the ADU is financed, income generated at current rental rates would provide a good passive income source to contribute to the mortgage on the primary dwelling or to help retirees pay for living costs.
While not for everyone, ADUs are a viable option not just for existing homes, but for brand new constructions as well.