Honolulu ADU and Ohana Unit Permits: Code Requirements, Lot Eligibility, and DPP Process

Ohana unit vs. ADU: the distinction matters

Honolulu has two separate legal frameworks for secondary dwelling units on single-family lots, and they operate under different rules:

The practical difference for your client: if they want to rent both units, the ADU framework may apply. If one unit will be owner-occupied, either framework may be available. Confirm which provision governs before designing, because the setback, size, and parking rules differ between them.

Lot eligibility requirements

Not every residential lot in Honolulu is eligible for a second unit. Common eligibility filters:

• Zoning district. Ohana units and ADUs are generally permitted in low-density residential districts (R-3.5 through R-10) and some apartment districts. They are not automatically permitted in all districts — check the use table for the specific zoning designation.
• Minimum lot size. The LUO sets a minimum lot area for eligibility. Under the ohana provisions, the lot must generally be at least 3,500 square feet, though some district-specific rules apply. The ADU provisions have their own lot size thresholds.
• Existing unit count. The provisions apply to lots that currently contain one single-family dwelling. A lot that already has an ohana unit or that has been converted to multi-family use is generally not eligible for an additional secondary unit under these provisions.
• No outstanding violations. DPP will check the permit history of the parcel. An existing unpermitted structure on the lot can block issuance of a new permit until the violation is resolved.

Setback modifications for accessory structures in the rear yard

One of the most consequential LUO provisions for ohana and ADU projects is the modified setback that applies to accessory structures located entirely within the rear yard area. Under this provision, a detached accessory structure in the rear yard may be sited closer to the rear and side property lines than the standard district setbacks — in some cases as close as 5 feet — provided specific conditions are met:

• The structure must be located entirely behind the primary dwelling
• The structure must not exceed a specified height limit (typically one story, or a reduced height limit compared to the primary dwelling)
• The structure must not occupy more than a specified percentage of the rear yard area

These modified setbacks are commonly misapplied. The most common errors: applying the reduced setbacks to a structure that is not entirely in the rear yard (a structure that extends beyond the rear wall of the primary dwelling does not qualify), and using the reduced setback for a structure that exceeds the allowable height under the modified rule.

Size limits and lot coverage impacts

Secondary units under both the ohana and ADU provisions are subject to maximum size limits. These limits are typically expressed as a maximum floor area (in square feet) or as a percentage of the primary dwelling's floor area, subject to an absolute cap. The ADU provisions have been updated by the Hawaii legislature and by City Council amendments over recent years — the current size limits should be verified against the adopted LUO text, not summarized guidance.

Lot coverage is a common compliance failure on ohana and ADU projects. The footprint of the secondary unit counts toward the lot's total lot coverage, along with the primary dwelling, covered parking, and any other covered structures. On smaller lots, the addition of a 600-square-foot ohana unit can push total lot coverage over the district maximum. This must be calculated before finalizing the design.

Parking requirements

The ohana and ADU provisions impose parking requirements for the secondary unit. One additional off-street parking stall is typically required for the secondary unit. This stall must meet dimensional requirements (minimum 8.5 feet wide by 18 feet deep for a standard stall) and must have unobstructed access to a public street or alley.

Tandem parking (two stalls arranged end-to-end in a single driveway) is permitted for ohana units in some configurations. Verify whether the specific project qualifies before designing a tandem arrangement.

State law has modified parking requirements for ADUs in transit-accessible areas. For parcels within a specified distance of a major transit corridor or bus rapid transit stop, parking requirements for the ADU may be reduced or waived. This is a frequently overlooked exception that can make otherwise-infeasible projects viable.

The DPP permit path

Ohana unit and ADU projects follow the standard building permit path or, if the certifying architect qualifies, the SCP path. There is no separate ohana-specific permit type — it is a building permit for a residential addition or new accessory structure, with the LUO analysis documented in the general notes and site plan.

Your general notes should include:

• Citation to the applicable LUO provision (ROH §21-4.90 for ohana or §21-4.100 for ADU)
• Confirmation of lot eligibility (zoning district, lot area, existing unit count)
• Proposed unit size and comparison to maximum allowed
• Lot coverage calculation including all structures
• Parking stall count and location
• Owner-occupancy declaration if required by the applicable provision