Hawaii Statewide Rule

Hawaii Requires Counties to Allow Accessory Dwelling Units (HRS 46-4.8)

Few RestrictionsApplies statewide across Hawaii (2026)

Key Facts

Statute: HRS §46-4.8
Enacted: Act 39, SLH 2024
Minimum required: Two ADUs per lot
County deadline: December 31, 2026
Applies to: Urban residentially zoned lots

Last verified: July 31, 2026

Summary

Hawaii's Act 39 (2024), codified at HRS §46-4.8, orders every county to allow at least two accessory dwelling units, or the reasonable equivalent, on all residentially zoned urban lots, adopting enabling ordinances by December 31, 2026, or granting such permits by default.

Except as provided in subsections (c) and (d), each county shall adopt or amend ordinances defining reasonable standards that allow for the construction of at least two accessory dwelling units, or the reasonable equivalent, for residential use on all residentially zoned lots.

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Full Breakdown

HRS §46-4.8, enacted as Act 39, Session Laws of Hawaii 2024, requires all four counties, Honolulu, Hawaii, Maui, and Kauai, to adopt or amend zoning ordinances allowing at least two accessory dwelling units, or the reasonable equivalent, on every residentially zoned lot inside the urban district. County development standards, setbacks, and lot-coverage limits still apply, and a county may deny a permit where utility infrastructure is insufficient. If a county misses the December 31, 2026 deadline, it cannot reject a permit for up to two ADUs on the basis of exceeding the maximum unit count. The mandate excludes agricultural and rural land, special management areas, and high natural-hazard zones.

Violations & Penalties

Counties enforce ADU limits through their own zoning ordinances, and unpermitted units face county building and zoning penalties. A county that misses the December 31, 2026 deadline may not deny an ADU permit for exceeding the maximum unit count.

Frequently Asked Questions

Does Hawaii let me build a tiny home as an accessory dwelling unit?

HRS §46-4.8 requires each county to allow at least two accessory dwelling units on residentially zoned urban lots, but the county sets the size, setback, and design standards a unit must meet.

What if my county hasn't updated its ADU ordinance by 2026?

Under §46-4.8(g), after December 31, 2026 the county cannot deny a permit for up to two ADUs based on exceeding the maximum unit count, though infrastructure and design standards still apply.

Where does the ADU mandate not apply?

It excludes land outside the urban district, agricultural and rural lots, special management areas, and urban zones at high risk of flooding, lava, or fire.

Sources

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