Honolulu Accessory Structure Permits: Sheds, Garages, and Ohana Units

What counts as an accessory structure?

Under ROH Chapter 21, an accessory structure is a structure that is subordinate in size and use to the principal dwelling on the lot, and customarily associated with the primary use. The category includes detached garages, carports, storage sheds, pool houses, workshops, and — importantly — ohana units (accessory dwelling units). A structure does not stop being an accessory structure because it has plumbing, HVAC, or is fully habitable.

What matters for permit threshold and setback purposes is the structure's relationship to the primary dwelling: is it subordinate in size, on the same lot, and associated with residential use?

When is a permit required?

The general rule under the ROH §16 building code (based on IBC 2018): any structure over 120 square feet requires a building permit. Structures at or under 120 sf may be exempt from the building code permit requirement, but they are not automatically exempt from zoning review.

Common situations that do require a permit even for small structures:

• Any structure attached to the main dwelling, regardless of size
• Any structure with electrical, plumbing, or mechanical systems
• Any structure with a permanent foundation
• Any structure used for habitation, including sleeping or cooking
• Any structure that, in combination with existing coverage, pushes lot coverage over the district maximum

A storage shed on a concrete slab, even if under 120 sf, requires a permit in most Honolulu residential zones because of the permanent foundation. When in doubt, call the DPP permit counter before you build.

Reduced setbacks for accessory structures

ROH §21-3.90 provides reduced setback standards for certain accessory structures in residential districts. To qualify for the reduced setbacks, the structure must meet all of the following:

• Detached from the primary dwelling (not connected by a covered walkway or breezeway)
• Maximum 200 square feet of floor area
• Maximum 15 feet in height
• Located in the rear yard only
• Not used for habitation (no sleeping, no kitchen)

Accessory structures meeting these criteria may have reduced rear and side yard setbacks — typically 3 feet in R-5 and smaller zones. The full district setbacks apply to any structure that does not qualify, and to any habitable accessory structure including ohana units.

The 200-sf and 15-ft thresholds are frequently misremembered as higher. Confirm against the current adopted ROH §21-3.90 text before designing to the reduced setbacks.

Ohana units: special requirements

An ohana unit is a secondary dwelling unit on a single-family lot. In Honolulu, ohana units in residential districts are governed by ROH §21-3.95 and require:

• Owner-occupancy: the owner must occupy either the primary unit or the ohana unit
• Minimum lot size: 3,500 sf (R-3.5 and R-5 districts)
• Full district setbacks — the reduced accessory structure setbacks do not apply
• One additional off-street parking stall (total of 3 for the lot)
• Maximum size: the smaller of 1,500 sf or 50% of the primary dwelling
• Maximum height: same as the district maximum for principal structures

Ohana unit permits require full plan check — they do not qualify for over-the-counter approval. The owner-occupancy requirement is enforced via a deed restriction recorded with the Bureau of Conveyances before the permit is finaled.

Note: state ADU legislation has modified some of these requirements. As of the 2026 session, verify current state ADU preemption rules against the local ROH provisions — the state has been progressively reducing local restrictions on accessory dwelling units.

Lot coverage: the binding constraint

For many Honolulu lots, the lot coverage limit — not the setback — is the binding constraint on accessory structure size. A 5,200 sf R-5 lot with a 1,100 sf house and 200 sf detached garage already has 1,300 sf of coverage (25%). The district permits 50%, leaving 1,300 sf of remaining capacity. A 400 sf ohana unit plus a 200 sf storage shed would bring total coverage to 1,900 sf (36.5%) — still under the limit.

But add a covered lanai, and that 18-inch overhang rule quickly eats into the remaining capacity. Use the Ikena Permit zoning calculator to model your lot coverage before designing.

Common mistakes and how to avoid them

• Applying reduced setbacks to habitable structures. The ROH §21-3.90 reduced setbacks only apply to non-habitable structures under 200 sf and 15 ft. An ohana unit with a kitchen and bathroom requires full district setbacks.
• Forgetting the parking requirement. Adding an ohana unit requires a third parking stall. On constrained lots, this can be impossible to achieve without a variance.
• Building without confirming lot coverage. DPP field-verifies lot coverage on inspection. Discrepancies between the plans and as-built conditions generate stop-work orders and re-inspection fees.
• Using the wrong code edition. Plans referencing superseded code editions generate immediate plan check corrections. Use IBC 2018 with current Hawaii amendments.