Building an ADU in Honolulu

What you can build here

Honolulu's Land Use Ordinance (LUO) defines an ADU as "a second dwelling unit, including separate kitchen, bedroom and bathroom facilities, attached or detached from the principal dwelling unit on the zoning lot." It is an accessory use in the Country district and the R-20, R-10, R-7.5, R-5 and R-3.5 residential districts.

You can build a new attached or detached structure, or convert a legally established structure, attic or basement. Only one ADU is allowed per zoning lot, even a lot with several existing homes. An ohana unit that is otherwise permitted doesn't count toward that limit, and an ohana unit may be added to a lot that already has an ADU if all standards are met. Ohana units must be lived in by people related to the family in the main house, except ohana units permitted before September 10, 1992.

ADUs aren't allowed on lots in planned development or cluster housing, or on landlocked lots. They are allowed only where there is enough infrastructure, including wastewater, water supply, roads and first-responder resources. [1]

Size, height and setbacks

Size. An ADU's total floor area can't exceed 500 square feet on a zoning lot of up to 4,999 square feet, or 1,000 square feet on a lot of 5,000 square feet or more.

Other standards. An ADU "must meet all development standards for the principal use in the underlying zoning district." In the residential districts, those include:

• Yards of 10 feet in front and 5 feet at the sides and rear for single-unit, two-unit and duplex dwellings
• A height limit of 25 to 30 feet, with extra setbacks for any part above 15 feet at the sides and rear
• Building area of no more than 50 percent of the lot, a floor area ratio of 0.7, and impervious surfaces of no more than 75 percent of the lot for homes permitted after May 1, 2019
• Limits on bathrooms per unit when a lot has two or more units: 2 on lots under 7,000 square feet, 3 on lots of 7,000 to 9,999, and 4 on larger lots

If the floor area ratio goes over 0.6, side and rear yards grow to 8 feet (R-3.5) or 11 feet (other R districts), and each unit must be owner-occupied. Confirm your exact limits with DPP. [1]

Parking

An ADU needs one off-street parking space on top of the main home's required parking. There are two exceptions:

• No space is needed for an ADU within 0.5 mile of a rail station.
• In the Primary Urban Center and Ewa development plan areas, the space is waived if the lot is within 800 feet of a city bus stop, unless a parking waiver has already been used for an ohana unit on the same lot.

[1]

Converting a garage or older accessory structure

You can convert a legally established structure into an ADU. If an accessory structure built before the ADU ordinance took effect is too big to meet the floor area limit, or there is no room for the parking space, you can apply for a zoning adjustment. The director must find that viable constraints don't allow reducing the floor area, or that no feasible parking site exists on the lot.

Zoning adjustments are filed online through HNL Build. The fees are a $200 initial review fee and a $400 processing fee. DPP decides whether the application is complete within 10 business days, and must decide within 45 calendar days of accepting it, or the permit is deemed approved. Call the Land Use Permits Division at (808) 768-8015 with questions. [1][3]

Renting it out and selling

Before you get a building permit, you must record a covenant that runs with the land. At a minimum it says:

• The ADU may be used only for long-term residential occupancy, not as a bed and breakfast home or transient vacation unit
• You and future owners can't put the lot under a condominium property regime to separate the ADU from the main home
• The restrictions lapse if the ADU is removed

Honolulu's LUO defines a transient vacation unit as a unit rented to transient occupants "for less than 90 consecutive days." Breaking the covenant is a violation of the LUO that DPP can enforce. [1]

Fees

DPP's building permit fee calculator estimates permit fees. The city's current wastewater system facility charge is $7,539 per ESDU, according to the Wastewater Branch.

The City Council created ADU fee incentives in 2016 (Ordinance 16-19). As proposed, the waiver covered building permit, grading and inspection fees and wastewater facility charges. The City Council passed Bill 63 (2024), CD1 on February 26, 2025. As passed, it moves the repeal date of those waiver provisions from June 30, 2025 to June 30, 2030. Ask DPP whether a waiver applies to your ADU before you budget. [4][5][6][7][8]

How state law affects Honolulu

Hawaii's Act 39 of 2024 (HRS 46-4.8) requires each county to allow at least two ADUs, "or the reasonable equivalent," on residentially zoned lots in the state urban district. If a county hasn't adopted its ordinance by December 31, 2026, it can't deny a permit for up to two ADUs just because the lot would exceed the maximum number of units. It can still deny one on infrastructure, design or development standards.

Honolulu's LUO, in DPP's May 2026 edition, allows one ADU per zoning lot, plus an ohana unit where one is permitted. Ask DPP how it will apply the state rule on your lot after December 31, 2026. See our Hawaii ADU law page for details. [1][9]

Outdated references on city forms

Some DPP forms and pages are older than the current LUO. The pre-application page still points to "ROH Sec. 21-8.20," and the zoning adjustment instructions cite "ROH Section 21-5.720"; in DPP's May 2026 edition of the LUO, the ADU rules are in Section 21-5.50-3(a) and the parking rule is in Section 21-6.30(b). The pre-check form is dated July 2016. Ask DPP if you aren't sure which version applies. [1][2][3][10]

Permit steps in Honolulu

1. Check your zoning and lot

   Look up your zoning district, lot size, flood zone and special district status with DPP's Property Search. Your lot size sets the ADU's maximum floor area. [1][2]

2. Get the ADU Public Facilities Pre-Check approved

   Submit the ADU Pre-Check Form with a plot plan and floor plan. DPP zoning, wastewater (DPP or the State Department of Health), the Board of Water Supply, the Fire Department and DPP roadway review each sign off. If any one says no, the ADU permit can't be granted. [10]

3. Record the ADU restrictive covenant

   Record a covenant with the State Bureau of Conveyances or Land Court using DPP's ADU covenant template. It limits the ADU to long-term occupancy and bars condo separation. [1][2]

4. Get a sewer capacity analysis, if needed

   An approved Sewer Capacity Analysis is required for new structures. Apply through DPP's Wastewater Branch; an approval is valid for two years. [2][4]

5. Run your plans through CivCheck

   Since September 1, 2026, ADU and ohana applications must go through DPP's CivCheck AI pre-application review first. Applications that skip it are rejected, and DPP recommends a design professional complete it. [11]

6. Apply in HNL Build and upload plans

   Apply online in HNL Build using your CivCheck ID, then upload plans to ePlans with the approved pre-check form and the recorded covenant. Plans are prescreened and routed to each review agency. [11][12]

7. Pay fees and get the permit

   Once all agencies approve, submit the remaining documents and pay the fees to have the building permit issued. [12]

8. Pass inspections and close the permit

   Call for all required inspections as you build, and make sure the inspector closes the permit when they are done. [12]

Who to call

• DPP Customer Service Division, residential building permits

  Building permits for single-family homes, duplexes and their accessory structures, including ADUs

  (808) 768-8220

  Honolulu Building Permit Center, 650 South King Street, Honolulu, HI 96813

  [13]

• DPP Land Use Permits Division

  Land Use Ordinance questions and zoning adjustments, such as converting an older accessory structure into an ADU

  (808) 768-8015

  [3][13]

• DPP Wastewater Branch

  Sewer capacity analysis and the wastewater line on the ADU pre-check form

  808-768-8210

  650 S. King St., 1st Floor, Honolulu, HI 96813

  [4]

• Kapolei Building Permit Center

  DPP satellite office, Monday to Friday, 7:45 a.m. to 4:30 p.m.

  1000 Uluohia Street, Kapolei, HI 96707

  [13]

Questions people ask