ADU Rules in Honolulu, HI (2026)
ADU rules, permit requirements, size limits, and fees for Honolulu, HI. Source-cited from official municipal code.
Yes, ADUs are allowed in Honolulu, HI.
Honolulu, HI permits accessory dwelling units (ADUs) on residential properties. ADUs — also called granny flats, in-law units, backyard cottages, or secondary suites — are secondary housing units on a single-family or multifamily lot. State and local law actively preempts local restrictions, making ADU approval a streamlined ministerial process. In Honolulu, the Honolulu Department of Planning and Permitting (DPP) handles ADU permit applications. Below you will find the current size limits, setbacks, fees, and timeline for building an ADU in Honolulu.
ADU Size Limits
ADU Size Limits in Honolulu: Detached ADU: up to 400 sq ft (max height: 25 feet). Attached ADU: No greater than 50% of primary dwelling floor area. Honolulu LUO Chapter 21 governs accessory dwelling units. Honolulu uses the term 'ohana dwelling unit' for ADUs — this is distinct from California's JADU concept. Hawaii Act 232 (2023) requires counties to allow ADUs by right. The ohana unit concept is documented in specialJurisdictionNotes. JADU (Junior Accessory Dwelling Unit) is a California-specific concept per California Government Code 65852.22 and is not applicable in Hawaii.
| Type | Max Size | Max Height |
|---|---|---|
| Detached ADU | 400 sq ft | 25 feet |
| Attached ADU | No greater than 50% of primary dwelling floor area | Per zone height limit |
Permit Fees
ADU Permit Fees in Honolulu: Plan check fee: $500–$3,000. Building permit fee: Based on construction value — typically $2,000–$7,000. Impact fees: Hawaii does not impose traditional impact fees; however, connection fees for Board of Water Supply and Hawaiian Electric apply. School fees: None or N/A. Total estimated permit cost: $5,000–$15,000 total fees depending on size and scope. Honolulu DPP fee schedule available at honoluludpp.org. Board of Water Supply (BWS) connection fees for new water service. Hawaiian Electric (HECO) interconnection fees for solar. Hawaii construction costs are among the highest in the US due to remote island supply chain.
| Fee Type | Amount |
|---|---|
| Plan Check | $500–$3,000 |
| Building Permit | Based on construction value — typically $2,000–$7,000 |
| Impact Fees | Hawaii does not impose traditional impact fees; however, connection fees for Board of Water Supply and Hawaiian Electric apply |
| School Fees | None |
| Total Estimate | $5,000–$15,000 total fees depending on size and scope |
Permit Timeline
Honolulu ADU Permit Timeline: Honolulu DPP building permit: typically 6-12 weeks plan check. Honolulu is known for slower permit processing. Construction typically 6-18 months. Act 232 requires ministerial approval for qualifying ADUs meeting objective standards. Apply through the Honolulu Department of Planning and Permitting (DPP) online permit portal. Phone: (808) 768-8000.
Setback Requirements
ADU Setback Requirements in Honolulu: Front setback: follows zone standard. Side setback: 5 feet. Rear setback: 5 feet. ADUs and accessory structures in Honolulu must maintain 5 ft rear and side setbacks in R-5 and larger zones. Smaller lots in R-3.5 zones may have different requirements. Hawaii Act 232 (2023) limits county authority to impose setbacks for ADUs more restrictive than those for primary dwellings. Honolulu LUO Chapter 21.
Parking Requirements
Parking Requirements: 1 parking space required per ADU. Parking requirement may be reduced or waived for ADUs within one-quarter mile of a TheBus or Skyline rail station per Act 232 and Honolulu transit access provisions.
Restrictions & Requirements
- ADU/ohana unit must be on same lot as primary residence
- Must comply with Honolulu LUO standards for the property's zone
- Cannot be sold separately from primary lot under standard subdivision rules
- Historic district properties (Downtown Honolulu, Chinatown) require design review
- Flood zone requirements apply in FEMA-mapped coastal SFHAs
- Short-term rental (TVU) use of ADU requires separate Transient Vacation Unit permit
How Many ADUs Are Allowed?
Number of ADUs Allowed in Honolulu: Single-family lots: 1 ADU (ohana unit) per single-family lot; Hawaii Act 232 may allow additional ADUs in some configurations. Multifamily properties: Multiple units permitted by right in A-1, A-2, A-3 apartment zones. Honolulu LUO allows one ohana (ADU) per R-zoned single-family lot. Hawaii Act 232 (2023) may expand ADU allowances further. A-zones allow multifamily by right.
Single-Family Lots
1 ADU (ohana unit) per single-family lot; Hawaii Act 232 may allow additional ADUs in some configurations
Multifamily Properties
Multiple units permitted by right in A-1, A-2, A-3 apartment zones
State Law & Preemption
State Preemption: Hawaii Act 232 (2023) preempts local ADU restrictions statewide — requires all counties to permit ADUs by right on single-family lots, limits restrictions on size and setbacks, and prohibits owner-occupancy requirements. The Hawaii State Legislature passed this law to address Hawaii's severe housing shortage. Honolulu has adopted local ADU rules consistent with Act 232.
Historic District Considerations
Historic District Requirements: Honolulu has 5 historic districts where additional design review may be required for ADU construction. Design review approval is required before obtaining a building permit for properties in historic overlay zones. Honolulu has 5 locally designated historic districts and numerous State Register historic properties. Downtown Honolulu/Chinatown Historic District is on the National Register of Historic Places. The Hawaii State Historic Preservation Division (SHPD) administers the State Historic Preservation Program. Locally, the Honolulu Historic Commission reviews exterior alterations to designated landmarks. Historic Kawaiahao Church, Iolani Palace (State Capitol Historic District), and the Chinatown area have strict review requirements. Look up historic district boundaries at: https://historichawaii.org/
Frequently Asked Questions
Can I build an ADU in Honolulu?
Yes. Honolulu, HI allows accessory dwelling units. On a single-family lot you can build 1 ADU (ohana unit) per single-family lot; Hawaii Act 232 may allow additional ADUs in some configurations.
How big can an ADU be in Honolulu?
The maximum size for a detached ADU in Honolulu is 400 square feet.
How long does it take to get an ADU permit in Honolulu?
The typical ADU permit timeline in Honolulu is Honolulu DPP building permit: typically 6-12 weeks plan check. Honolulu is known for slower permit processing. Construction typically 6-18 months. Act 232 requires ministerial approval for qualifying ADUs meeting objective standards.. Total estimated permit fees are $5,000–$15,000 total fees depending on size and scope.
Do I need extra parking for an ADU in Honolulu?
No, Honolulu does not require additional parking for ADUs.
Do I have to live on-site to have an ADU in Honolulu?
No, owner-occupancy is not required for ADUs in Honolulu.
Source: Revised Ordinances of Honolulu Chapter 21 (Land Use Ordinance); Hawaii Revised Statutes Section 46-4.5 (Act 232, 2023). Last verified April 6, 2026. View source