ADU Rules in Honolulu, Hawaii

Honolulu is Hawaii's capital and the only incorporated municipality in the City and County of Honolulu, which governs the entire island of Oahu. Hawaii has allowed "ohana dwelling units" (ADUs) since the 1980s. Hawaii Act 245 (2022) required all Hawaii counties to adopt ADU ordinances, and Honolulu enacted Ordinance 22-7 (effective 2023) with updated ADU standards.

Hawaii State ADU Law (Act 245, 2022)

Hawaii Act 245 (SB 3202), effective 2022, requires Hawaii counties to:

• Allow ADUs in residential zones by right
• Streamline ADU permitting
• Expand ADU size allowances

Honolulu ADU Framework

Honolulu's Land Use Ordinance (LUO) governs ohana/ADU standards. Honolulu Ordinance 22-7 (2023) expanded ADU allowances.

Permitted ADU Types

• Detached Ohana Unit (ADU): Standalone structure on the lot
• Attached Ohana Unit: Addition to primary dwelling with own entrance
• Accessory Dwelling Unit (interior): Interior conversion

Size Limits

• Standard ADU: Up to 800 sq ft (expanded under Ord. 22-7)
• Varies by zone — contact DPP for current standards
• Historical ohana limit was smaller; recent ordinance expanded allowances

Setbacks

Per Honolulu LUO for residential zones:

• Front: Per base zone
• Side: 5 feet minimum
• Rear: 5 feet minimum

Height

• Detached ADU: Per zone height limit (typically 25–30 feet)

Unique Hawaii Considerations

• Land Use Commission: Hawaii has state-level land use zoning. Most residential areas are in Urban District, which is required for ADUs
• Soil/Geological: Some Oahu properties have soil or geological concerns (volcanic rock, expansive soils)
• Coastal/Shoreline: Properties near the shoreline are subject to Hawaii's coastal zone management requirements

Permit Process

1. Verify zoning: Confirm Urban District designation and Honolulu zone
2. Pre-application: Contact DPP for pre-application consultation
3. Submit permit application: City & County of Honolulu DPP
4. Building permit: Honolulu Building Code applies
5. Inspections and CO: Required before occupancy

Contact

City & County of Honolulu Department of Planning and Permitting 650 South King Street, 7th Floor, Honolulu, HI 96813 Phone: (808) 768-8000 Website: honolulu.gov/dpp

Disclaimer: Honolulu's ADU ordinance was updated in 2023. Verify current standards with the DPP before starting any project.