Big Island ADU Rules Change: What Homeowners Need to Know

In October 2024, Hawai‘i County passed major updates to its housing regulations, replacing the former Ohana Dwelling system with new Accessory Dwelling Unit (ADU) rules. This shift opens up expanded opportunities for property owners across Big Island to build rental units, guest houses, or multi-generational housing—while following the latest zoning and permitting requirements. Below, we break down exactly what homeowners, investors, and builders need to know about Hawai‘i County’s new ADU laws.

From Ohana to ADU: What’s Changed?

On October 7, 2024, Hawai‘i County adopted Bill 123, effectively aligning local regulations with State Senate Bill 3202/Act 39. Consequentially, this change eliminates the older Ohana Dwelling Permit system and replaces it with a streamlined ADU approach. ADUs can now be added more broadly to residential lots—paving the way for expanded housing opportunities across the island.

Key Definition:

An Accessory Dwelling Unit (ADU) is a structure (attached or detached) designed for single family occupancy and includes one kitchen. Think of it as a flexible add-on living space that could serve family, guests, or even long-term renters.

Where Are ADUs Allowed?

ADUs are now permitted in the following zoning districts:

• RS (Residential)
• RD (Double Family Residential)
• RA (Residential-Agricultural)
• FA (Family-Agricultural)
• A (Agricultural)*

*Note: ADUs in Agricultural zones must fall within the State Land Use Urban or Rural districts. For properties in the Agricultural land use district, different farm dwelling rules apply.

How Many Units Can You Build?

The bill allows up to three ADUs per building site, a significant increase. For lots allowed to host more than one primary dwelling, each primary residence may also have its own ADU. For example:

• A 20,000 sq ft lot zoned RS-10 can host 2 main dwellings + 2 ADUs = 4 total dwellings.

You can build attached units (like a duplex), but only up to two connected units per structure to avoid triggering multi-family zoning requirements.

Size, Setbacks and System Requirements

Here are some of the new standards you’ll need to follow:

• Size: ADUs must not exceed 1,250 sq ft of living space (excluding lanais, garages, carports).
• Height: Must comply with the zoning district’s height limitations.
• Setbacks: Standard setbacks apply, with a minimum 15 feet between main buildings.
• Water & Wastewater: Must have approved systems—either county-provided or private (e.g., septic and rain catchment).
• Parking: Off-street parking requirements apply, based on the specific zoning.

What About Ohana Permits?

The County will continue to honor previously approved Ohana Dwelling Permits. This may be helpful for some homeowners, as these permits might allow larger structures (over 1,250 sq ft) depending on their original conditions.

Special Considerations

• Prohibited Areas: ADUs are not allowed in conservation districts, certain affordable housing developments, or where a change-of-zone ordinance explicitly prohibits them.
• SMA Zones: If your property is in a Special Management Area (SMA), you’ll need an SMA Assessment or permit.
• Short-Term Rentals: Only one ADU per site may be used as a transient accommodation rental (TAR), and only if no other TARs exist on the property.

The Permitting Process

Applying for an ADU is now more streamlined:

• Submit your building permit through the Department of Public Works.
• The Planning Department will handle land use review (no separate ADU application required).
• Your plan must include water/wastewater compliance and will be reviewed accordingly.

Frequently Asked Questions

Can I build a guest house on my property in Hawai‘i?
Yes — under the new ADU rules, many Big Island property owners can build detached or attached guest houses (ADUs) depending on their zoning.

How many ADUs can I build on Big Island?
Under the new Big Island ADU rules, you may be allowed up to 3 ADUs per lot, depending on lot size and zoning classification.

Do I need a permit for an ADU in Hawai‘i?
Yes — the new Big Island ADU rules still require a building permit and compliance with zoning, water, wastewater, and setback regulations.

Final Thoughts

The shift from Ohana Dwellings to ADUs on Big Island represents a bold effort to meet housing needs without compromising community standards. With more flexible rules and greater capacity, property owners now have new tools to create space for multi-generational living, long-term rentals, or guest accommodations, all while staying code-compliant.

If you're considering adding an ADU to your property or want to learn how these changes impact your real estate goals, now is a great time to start the conversation. Reach out today!

? Marco@KonaLuxuryRealEstate.com
? 808.557.8921