ADU Regulations in Hawaii (HI)
Hawaii is rated Moderate for ADU construction with an ADU-friendliness score of 75/100 (Very ADU-Friendly). Hawaii has a statewide ADU law that sets baseline rules across all municipalities. No owner-occupancy requirement. No additional parking required for ADUs. Hawaii passed Act 232 (2023), requiring all counties to allow ADUs on residentially zoned lots. Counties must permit at least one ADU per lot. The law limits parking requirements and setback mandates. High land costs make ADUs a critical housing strategy in Hawaii.
Full ADU Regulations Summary for Hawaii
| ADUs Allowed | Yes |
| Statewide ADU Law | Yes |
| Maximum ADU Size | 800 sq ft |
| Owner Occupancy Required | No |
| Parking Required | No |
| Minimum Setback | 5 ft |
| Permitting Timeline | Varies by county |
| Impact Fees | Varies by county |
| Long-Term Rental Allowed | Yes |
| Short-Term Rental (Airbnb) Allowed | No |
| Ease of Building | Moderate |
ADU Regulations by City in Hawaii
ADU rules can vary by city even within the same state. While Hawaii's statewide law sets minimum standards, some cities have additional local provisions. Below are ADU details for 3 cities in Hawaii.
Honolulu
ADUs allowed on most residential lots. Honolulu permits both attached and detached ADUs. Maximum 800 sq ft. Permit processing times average 6-12 months due to infrastructure reviews.
Maui (Kahului)
ADUs permitted per county regulations. Maui County allows one ADU per lot in residential zones.
Hilo
ADUs allowed in residential zones. Hawaii County has relatively straightforward ADU permitting.
How Hawaii Compares to Other States
Below is a comparison of Hawaii with five states that have similar ADU-friendliness scores. This comparison helps illustrate where Hawaii stands nationally.
| State | Score | Statewide Law | Parking Req? | Owner Occ? | Ease |
|---|---|---|---|---|---|
| Hawaii (HI) | 75 | Yes | No | No | Moderate |
| Virginia (VA) | 75 | Yes | No | No | Moderate |
| New York (NY) | 76 | Yes | No | Yes | Easy |
| Florida (FL) | 78 | Yes | No | No | Easy |
| Montana (MT) | 78 | Yes | No | No | Easy |
| Nevada (NV) | 78 | Yes | No | No | Moderate |
Frequently Asked Questions About ADUs in Hawaii
Can I build an ADU in Hawaii?
Yes, ADUs are allowed in Hawaii. Hawaii has a statewide ADU law that requires local jurisdictions to permit ADUs on residential lots. This means your city cannot outright ban ADUs. The ease of building is rated "Moderate" with a friendliness score of 75/100.
Do I need to live on the property to have an ADU in Hawaii?
No, Hawaii does not require owner occupancy for ADUs. You can rent out both the main house and the ADU, which maximizes rental income potential.
How big can an ADU be in Hawaii?
The state maximum ADU size in Hawaii is 800 square feet. Local jurisdictions may set lower limits. Some cities also limit ADU size to a percentage of the primary dwelling (e.g., 50%).
Do I need extra parking for an ADU in Hawaii?
No, Hawaii does not require additional parking for ADUs. This is a significant advantage, as parking requirements are often the biggest barrier to ADU construction on smaller lots.
Can I rent out my ADU in Hawaii?
Yes, long-term rentals of ADUs are allowed in Hawaii. However, short-term rentals (like Airbnb) of ADUs are restricted in Hawaii. You can rent your ADU for long-term tenants but not as a vacation rental.
How long does it take to get an ADU permit in Hawaii?
The permitting timeline in Hawaii is: Varies by county. The statewide law sets maximum review periods that cities must comply with. Actual timelines can be affected by plan review backlogs, inspection scheduling, and the complexity of your project. Pre-approved ADU plans, where available, can significantly speed up the process.
Check ADU Rules for Your City
Use our ADU regulations lookup tool to find the specific rules for your city in Hawaii, or browse all 50 states to compare ADU regulations across the country. Remember that local rules may be more specific than state-level regulations.