ADU Laws in Hawaii (2026)
Hawaii state ADU law details, key provisions, preemption status, and recent legislative changes for accessory dwelling units.
Law Name
Hawaii Act 232 (2023) — Relating to Accessory Dwelling Units
Effective Date
2023-07-06
Preempts Local Ordinances
Yes — state law overrides local restrictions
Has State Law
Yes
Key Provisions
Requires all Hawaii counties to permit ADUs by right on single-family and duplex lots in residential zones
ADUs must receive ministerial approval — no special permit, conditional use permit, or variance required
Counties may not impose owner-occupancy requirements on ADU applicants
ADUs may be attached, detached, or converted from existing space
Counties may establish reasonable design and dimensional standards but cannot effectively prohibit ADUs
Maximum ADU size regulations must allow at least 800 square feet or 60% of the primary dwelling, whichever is greater
Parking requirements may not exceed one space per ADU
ADU permitting must be processed within 60 days of complete application
Hawaii's high housing costs and limited land make ADU legalization particularly impactful statewide
Legislative History
2023 — Act 232 (HB 1630)
Hawaii enacted comprehensive ADU reform requiring all counties (Honolulu, Maui, Kauai, Hawaii County) to allow ADUs by right in residential zones. Eliminated owner-occupancy requirements. Effective July 6, 2023. Addresses Hawaii's severe housing shortage by enabling more residential density on existing lots.
Official Sources
What Does Preemption Mean for Local Cities?
Because Hawaii law preempts local ordinances, individual cities cannot impose restrictions stricter than the state standard. A city may still have additional administrative requirements, but cannot deny ADU applications that comply with state minimums.
Learn about Hawaiizoning preemption →Source: Hawaii Act 232 (2023) — Relating to Accessory Dwelling Units. Last verified April 5, 2026. View source