ADU Downloads & FAQ’s


ADU – Instructions and Filing a Declaration of Restrictive Covenants 8/9/2017 Download
Building Permit ADU – Quick Guide 6/21/2017 Download
Building Permit ADU Director’s Report 9/28/2015 Download
Building Permit ADU FAQ 4/1/2016 Download
Building Permit ADU Public Facilities Pre-Check Form 6/1/2017 Download


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The following are common questions about an accessory dwelling unit, also known as an ADU. The answers are based on the ADU Ordinance that was signed by Mayor Kirk Caldwell on September 14, 2015.

If you would like to learn more about how to add an ADU to your lot, please visit our website at

1.  What is an Accessory Dwelling Unit?

An ADU is an accessory or second dwelling unit, including its own kitchen, bedroom, and bathroom facilities, attached or detached from the primary dwelling unit on the zoning lot. ADUs are intended to be “accessory” to the main house, and are typically much smaller and sited to the rear or side of the house.

2.  Why are ADUs important?

As identified in the Mayor’s Affordable Housing Strategy, there is a major shortage of affordable housing on Oahu, especially for rental housing. ADUs can help address this problem by allowing existing homeowners to build a second unit on their property. In addition, seniors will have the option to “[amazon_textlink asin=’0470056142′ text=’age in place’ template=’ProductLink’ store=’ownbuilddesig-20′ marketplace=’US’ link_id=’912413a1-9f50-11e7-bb25-39206c0395e1′]” by moving into the ADU and renting the larger home for additional income.

3.  Where can I build an ADU?

An ADU can be built on any lot zoned Residential (R-3.5, R-5, R-7.5, R-10, and R-20) or Country District with a lot area of 3,500 square feet (SF) or more provided that there is adequate infrastructure and subject to meeting all other Land Use Ordinance provisions for the zoning lot and there are no restrictive covenants.

4.  How big can an accessory dwelling unit be?

An ADU can be a maximum of 400 SF for lots ranging between 3,500 SF and 4,999 SF and 800 SF for lots greater than 5,000 SF.

5.  In addition to the principal dwelling unit, how many ADUs can I build on a single lot?

Only one additional dwelling unit is permitted. ADUs are not permitted on lots that already have more than one dwelling unit, including but not necessarily limited to, more than one single-family dwelling, a two-family dwelling, accessory authorized ohana dwelling, or guest house. Properties with multi-family dwellings, or which are part of a planned development housing, cluster, or group living facility are also not eligible.

6.  How are ADUs different from ohana dwelling units?

ADUs are similar, but not synonymous with ohana dwelling units. The key difference is that ohana dwellings restrcit occupancy to family members, have no size limitations, and require two off-street parking spaces. The ADU regulations allow occupancy of the ADU by non-family members, require only one off-street parking space, and limit the size of the ADU.

7. Are owners of an accessory dwelling unit required to live on the property?

Yes, either the ADU or primary dwelling unit must be occupied by the property owner(s), or persons who are related by blood, marriage, or adoption to the property owner(s), or designated authorized representative(s), except in unforseen hardship circumstances (i.e., active military deployment, serious illness).

8.  Is there a minimum occupancy period for an ADU?

Yes, an ADU may not be occupied for less than a six month (180 days) period.

9.  Is there enough sewer and water capacity to accommodate ADUs?

Sewer and water capacity varies from location to location. To assure the adequacy of the existing infrastructure, prospective applicants will need to receive confirmation from all appropriate agencies (The Department of Planning and Permitting’s (DPP) Customer Service Division; Wastewater Branch; and Traffic Review Branch, State Department of Health, Board of Water Supply, and Honolulu Fire Department), affirming the capacity of needed infrastructure. The DPP has developed a step-by-step Public Facilities Pre-Check Form for homeowners or contractors to get the required approvals. No building permit for ADUs shall be issued unless there is adequate infrastructure to support it.

10.  Is parking required for an ADU?

The ADU law requires one parking space to be located on the lot per ADU, in addition to the required parking for the primary dwelling unit. Tandem parking and compact stalls are permitted. However, ADUs within one-half mile of a rail transit station do not require parking.

11.  Can the owner sell the ADU or the portion of the parcel where the ADU is located?

No, ADUs are not allowed to be sold separately. They are intended to provide rental housing. The owner(s) of the lot are required to record a covenant stipulating that neither the owner(s), nor their heirs, successors, nor assigns will submit the lot or any portion thereof to a condominium property regime to separate the ownership of an ADU from the ownership of its primary dwelling unit.

12.  How does the ADU law guard against using the units as illegal vacation rentals?

The ADU provisions require the ADU to be leased for a minimum of six months (180 days). This requirement will be recorded in a covenant running with the land with the Bureau of Conveyances or the Land Court of the State of Hawaii, or both, as is appropriate. This requirement facilitates enforcement and deters the ADU from being used as a transient vacation unit.

13.  What are the different ways by which I can add an ADU to a lot?

You can build a new unit either separate or attached. An existing accessory dwelling unit structure (garage or interior rooms such as recreation rooms, basements or attics) can also be converted to an ADU. Current building code standards must be met when adding an ADU.

14.  Is a building permit required to convert an ohana dwelling unit or other accessory structures into an ADU?

Yes, a building permit is required to convert an ohana dwelling unit or an accessory structure or interior room into an ADU.

15.  Can a nonconforming structure be converted to an ADU?

Yes, a nonconforming structure can be converted to an ADU, but it has to conform to the ADU regulations and all the development standards of the underlying zoning district, as well as other pertinent regulations.

16.  How can I convert an existing, legally established accessory structure to an accessory dwelling unit if it was built prior to the effective date of the ADU Ordinance, but does not meet the size and off-street requirements?

An existing, legally established accessory dwelling unit constructed in a residential district prior to the effective date of the ADU Ordinance may be converted to an ADU and allowed to exceed the maximum floor area and/or be exempted from the off-street parking requirement through a zoning adjustment process. The DPP has prepared instructions for prospective Applicants to use when requesting a zoning adjustment.

17. How can I convert an existing structure to an ADU, if it was built without a building permit?

The owner must obtain an after-the-fact In addition to fulfilling the base requirements of the after-the-fact permit, any adjustments required to the structure must conform to the ADU regulations.

18.  Can pre-manufactured, container, modular, or mobile homes be used as an ADU?

Yes, these are just construction methods. They can be used as ADUs, provided they comply with the provisions related to ADUs and all applicable building codes.

19.  If a private covenant stipulates that I cannot have an accessory dwelling unit, can I still build an ADU?

No, while the accessory dwelling unit Ordinance allows ADUs if a private covenant prohibits the construction of an ADU, the latter takes precedence. In such situations, these prohibitions must be addressed with the appropriate parties, not the City. The appropriate association must take action to lift the restriction.

20.  Will an accessory dwelling unit change the character of my neighborhood?

ADU provisions are intended to maintain the character of neighborhoods. The overall size of the ADU is limited, coupled with the one ADU per lot requirement; both will help minimize the visual impact to the neighborhood. In addition, all development standards and siting requirements of the underlying zoning district must be met. Similarly, the small size of the ADU will limit the number of people occupying the ADU. In addition, the occupancy requirement of the owner(s) will ensure that tenants are well behaved.

21.  How is the City making it easier to build an accessory dwelling unit?

The DPP has developed an ADU brochure to help guide homeowners and contractors through the permitting process.  We are also working with the building industry and design professionals to encourage them to develop a range of building types, both stand-alone cottages and additions, which can be pre-approved under a master permit. Once a builder obtains a master permit for a particular model, that building just needs a site permit showing where and how it will be constructed on the lot (but will require appropriate inspections during construction). We are also encouraging financial institutions and builders to develop simplified financing packages, similar to a home equity loan.