Is ADU Right for You?

Everything you need to know about the potential to add an accessory dwelling unit to your property.

In an effort to create more affordable housing on Oahu, the City and County of Honolulu is putting some of the power in homeowners’ hands by encouraging them to offer legal, long-term rentals on their properties in the form of accessory dwelling units or ADUs.

An ADU can either be attached to or detached from the primary residence on the property. It’s typically much smaller, but has everything a person needs to call the space home: at minimum, a kitchen, bedroom and bathroom.

“The ADU is one of the first pieces of the housing strategy,” says Harrison Rue, community building and transit-oriented development administrator for the City and County of Honolulu. “It’s really trying to address the dire need for more affordable and workforce housing, particularly for rentals. It’s a way to enlist the entire community in trying to help fill the need for housing by the city getting out of the way and passing regulations for many, or most, homeowners to build or convert a small rental unit on their property.”

The ADU can be attached to the main house or it can be a separate structure. Much of that will depend on the property owner’s personal preference, and also how the lot is designed — especially where the main house is situated.

If the property is less than 5,000 square feet, the ADU can be no larger than 400 square feet. If the property is larger than 5,000 square feet, the ADU can be as big as 800 square feet.

While 400 square feet may not sound like a lot of space to live in, it certainly can be done, and it won’t necessarily feel small. “The way to make a small unit feel bigger is to vault the ceiling,” says Evan Fujimoto of Graham Builders Inc.

An uncovered lanai will also give the ADU more usable space without affecting the square footage, notes Marshall Hickox of Homeworks Construction Inc. “You can put a trellis over it and that won’t count as covered area. You won’t get full protection from the rain, but you can get nice shade,” he says. Inside, he adds, a bay window over the kitchen sink can make the interior feel larger.
Before getting too far into the design process, it’s important to ensure your property is eligible for an ADU. “The most important thing is the pre-planning,” Hickox says. “Before you invest too much money in the design, make sure you qualify.”

The Department of Planning and Permitting has an optional pre-check form for homeowners to determine whether the lot has adequate infrastructure capacity to build an ADU. The form guides homeowners through the process of whether the lot meets various requirements, including zoning, wastewater disposal, adequate water system and more. Homeworks Construction offers a paid service to route the form for its clients and, if approved, will credit the money spent toward the project.

As of mid-January, the City and County of Honolulu had only approved one new ADU building permit, and one building permit to convert an ohana unit into an ADU. Twenty-nine building-permit applications with plans have been received and are pending.

As noted, an existing ohana unit can be converted into an ADU, which would allow the homeowner to rent it to someone who is not a family member. The main differences between ADUs and ohana units are that ohana units can only be occupied by family members, require two off-street parking spaces and have no size restrictions. ADUs, meanwhile, can be rented by non-members of the family (but must be rented for at least six months at a time), require one off-street parking space (unless it’s within a half-mile of a rail station) and have size restrictions.

While they can be rented to anyone, ADUs are a great option for family members, especially seniors. They can either remain living in the primary residence while renting the ADU to a family member, or can move to the ADU while a family member — such as an adult son or daughter with young children of his or her own — lives in the main house. It may be a great option for caregiving.

An ADU that Graham Builders is designing is a perfect example. The parents, now in their 60s, will live in the main house, while their adult son will live in the ADU. Sometime in the next 20 years, they plan to switch places, with the parents downsizing to the ADU and their son — maybe then with a family of his own — will move into the main house.

“There are a lot of benefits for homeowners to consider adding an ADU,” Rue says. “It’s something that will certainly add to the value of your home and will provide extra income over time. If you happen to be an elderly person or middle-age and would like to stay in the neighborhood, you can build a unit that can be your own accessible unit for aging in place.”

There are restrictions and rules to follow, though. Offsite management is not permitted. Either the ADU or the main residence must be occupied by the property owner, a family member or a designated, authorized representative, with the exception of certain cases, such as military deployment and serious illness.

If and when the property is sold, both structures are sold together — the ADU cannot be sold separately.

Ready to learn more? Review the steps to take before you build, and see if your property meets the basic requirements. Then, submit an optional ADU pre-check form, available at, to help guide you through the eligibility process.

Categories: Expert Advice, Industry Insider, Small Spaces