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: size varies by zoning — see official source (max height: varies — see official source). Attached ADU: size varies by zoning — see official source.
| Type | Max Size | Max Height |
|---|---|---|
| Detached ADU | See official source | See official source |
| Attached ADU | See official source | See official source |
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: Varies.
| 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 | See official source |
Permit Timeline
Honolulu ADU Permit Timeline: No specific processing deadline found in amlegal fetch. HRS §46-4.8 requires ministerial approval; specific Honolulu processing timeline not retrieved. 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: no minimum. Rear setback: no minimum.
Parking Requirements
Parking Requirements: Parking requirements per §21-6.30(d) — not retrieved in 2026-06-04 amlegal fetch. See §21-6.30 for adjustments applicable to home occupations and ADUs.
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
Statewide Preemption
ADU Preemption
Hawaii state law preempts local ADU rules — local governments cannot impose stricter standards.
View Hawaii preemption detailsState 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 See §21-5.50-3 — not retrieved in 2026-06-04 amlegal fetch square feet.
How long does it take to get an ADU permit in Honolulu?
The typical ADU permit timeline in Honolulu is No specific processing deadline found in amlegal fetch. HRS §46-4.8 requires ministerial approval; specific Honolulu processing timeline not retrieved.. Total estimated permit fees are Fee schedule not retrieved. Building permit fees per Chapter 18 based on construction valuation. Board of Water Supply and HECO connection fees also apply..
Do I need extra parking for an ADU in Honolulu?
Honolulu parking rules for ADUs: Parking requirements per §21-6.30(d) — not retrieved in 2026-06-04 amlegal fetch. See §21-6.30 for adjustments applicable to home occupations and ADUs.
Do I have to live on-site to have an ADU in Honolulu?
Owner-occupancy requirement in Honolulu: Ohana units must be occupied by family members (§21-5.50(c)(2)); ADU-specific occupancy requirements per §21-5.50-3 not retrieved.
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