How to Get an ADU Permit in Honolulu: Step by Step

Can I build an ADU on my lot?

Start with the lot, not the floor plan. DPP's Property Search shows a parcel's zoning, flood hazard, special districts and management areas, lot size, existing permits and any notices of violation. Look them up before anyone draws.

A few results change the plan early:

• Zoning. Act 39 (2024) aims ADU rules at residentially zoned lots, which it defines as lots principally reserved for single-family and two-family detached dwellings.
• Flood hazard or a Special Management Area. DPP requires plans stamped by a licensed professional for work in a special management area, flood hazard area or special design district.
• Open permits or violations, which are better found now than during review.
• A condominium property regime (CPR). DPP notes that a CPR parcel is not a zoning lot and does not increase development potential; standards apply to the whole zoning lot.

Lot coverage matters too. DPP's building permit FAQ says impervious surfaces, including rooftops, driveways and patios, must not exceed 75% of the zoning lot area, and a new unit adds roof.

What does DPP need before the building permit?

DPP lists the approvals an ADU or ohana unit needs first. Without them, it says, review of the building permit application will be rejected or suspended until they are obtained.

The 210-day window is the one to plan around. Start the pre-check when the design is far enough along to finish the covenant, the sewer review and the plans inside it.

How does CivCheck fit in?

DPP uses CivCheck, a free AI plan-review tool, to screen residential applications before they enter official review. ADUs and ohana units are on its list of eligible projects, along with new homes, additions and alterations. DPP says CivCheck is required only for the first submission, and that only plans carrying the CivCheck watermark should be uploaded to HNL Build.

DPP reports that applications prepared with CivCheck reached a permit decision 55% faster on average: 32.5 days, compared with 73 days without it. Those are DPP's averages, not a promise for any one project. DPP also describes permit times as highly variable.

What else can the review flag?

The building permit goes to more than one reviewer. DPP lists, among others:

• The Board of Water Supply, for water use and adequacy.
• The Wastewater Branch, for sewer availability and adequacy.
• The Civil Engineering Branch, for drainage, grading and work near streams.
• The State Historic Preservation Division, for any parcel with a structure 50 or more years old.
• The Department of Health, if the lot uses a private wastewater system such as a septic tank.

Parking is part of zoning review. DPP's FAQ says an additional parking space is required for an ADU, although parking is not required in certain areas near future rail stations.

Some lots need approvals from outside DPP as well. DPP names the Ewa Villages Owner's Association, the Department of Hawaiian Home Lands and the State Historic Preservation Division.

What does Act 39 change for Oahu ADUs?

Act 39 (2024) requires each county to adopt or amend ordinances that allow at least two ADUs, or the reasonable equivalent, on residentially zoned lots, or to define districts that do. If a county has not done so by December 31, 2026, it may not deny a permit for up to two ADUs on a single-family lot on the basis of exceeding the maximum number of housing units. It can still deny on infrastructure, design or development standards.

The act does not apply outside the State urban district, to county powers within special management areas, or in urban areas a county deems at high risk of flooding, lava or fire. Private covenants recorded after the act took effect cannot limit ADUs below what it allows; covenants recorded earlier are not affected.

Honolulu also updated its Land Use Ordinance. Ordinance 25-2 was signed on January 3, 2025, and most of its amendments took effect on September 30, 2025, according to DPP. Confirm the current rules for your lot with DPP before you design.

What should an ADU estimate cover?

A turnkey ADU price only means something if it lists the steps it includes. Ask for the pre-check, the covenant, the sewer capacity analysis, the plans, the permit application, construction, utility connections and the licensed electrical and plumbing work to be named.

Then check the contractor's license. An ADU uses many trades, which makes it general building contractor work under HRS §444-7. If you are paying with a home equity line, our HELOC guide covers drawing funds as the contractor's payments come due.

Ward Design Center designs, permits and builds ADUs and ohana units across Oahu as one turnkey job. Every ADU is quoted after a site visit; your written estimate is the price that counts. See our ADU builders page, read about ADUs in Honolulu and ADUs in Kapolei, or request a free estimate.