ADUs in Hawaii: What Real Estate Investors Need to Know in 2026

Hawaii's ADU landscape shifted significantly in 2024 when Governor Green signed SB 3202 (Act 39) into law, requiring all counties to allow at least two accessory dwelling units on residentially zoned lots by December 31, 2026. For real estate investors, ADUs represent a compelling opportunity to generate rental income, increase property value, and tap into Hawaii's persistent housing demand—but key restrictions apply.

Hawaii's housing market has always rewarded investors who move early on the right opportunity. Limited land, consistent demand, and a population that consistently outpaces available inventory create conditions that are difficult to replicate elsewhere. ADUs—accessory dwelling units—are quickly becoming one of the most discussed strategies among Hawaii investors, and for good reason.

New state legislation has unlocked pathways that simply did not exist a few years ago. Whether you own a property on Oahu or the Big Island, understanding what has changed—and what restrictions remain—can be the difference between a well-positioned investment and a costly misstep.

What Is an ADU?

An accessory dwelling unit is a second, self-contained living space built on the same lot as a primary single-family home. ADUs include a full kitchen (with an oven, range, refrigerator, and sink), a bathroom, and a sleeping area.

There are three main configurations:

• Detached ADU: A standalone structure separate from the main home—think a backyard cottage or ohana unit.

• Attached ADU: A new addition connected to the primary dwelling but with its own entrance.

• Interior/Conversion ADU: An existing space—like a garage or enclosed lanai—converted into a legal dwelling unit.

On Oahu, ADUs were first introduced in 2015 as part of an effort to address the island's housing shortage. They have since gained traction statewide as a practical tool for increasing rental supply without requiring new land development.

Hawaii's New ADU Laws: What Bill 123 and Act 39 Change for Investors

The most significant legislative development in Hawaii's ADU landscape came in May 2024, when Governor Josh Green signed Senate Bill 3202 into law as Act 39. The law requires all Hawaii counties to adopt or amend their ordinances—no later than December 31, 2026—to allow at least two ADUs on all residentially zoned lots. It also prohibits private covenants from restricting ADU construction below what state law permits, and from limiting the long-term rental of residential units.

At the county level, Hawaii County (Big Island) passed Bill 123, which goes further than the state minimum. Under Bill 123:

• Homeowners in residential and agricultural zoning districts can build up to three ADUs on a single property (the Big Island's larger lot sizes made this feasible).

• Each ADU is capped at 1,250 square feet of living area, not counting garages, lanais, or carports.

• ADUs may be attached or detached from the primary structure.

• Only one ADU per property may be used as a short-term vacation rental.

• Bill 123 also eliminates the old duplicative "ohana dwelling" permit process, streamlining the path to approval.

For Oahu investors, the City and County of Honolulu's Department of Planning and Permitting (DPP) continues to govern ADU construction. Existing Oahu rules require lots to be a minimum of 3,500 square feet, with allowable ADU sizes ranging from 400 square feet (for lots between 3,500–4,999 sq ft) to 800 square feet (for lots of 5,000 sq ft or more). As counties finalize their compliance with Act 39 ahead of the December 2026 deadline, additional rule updates are expected.

Key Benefits of ADUs for Real Estate Investors

The investment case for ADUs in Hawaii is straightforward. Here is why experienced investors are paying close attention:

Rental income without acquiring new land. Since you already own the underlying lot, the primary acquisition cost is eliminated. The only capital required is the cost of construction—which, according to contractors across Hawaii, generally runs between $200 and $400 per square foot, with most estimates landing in the $250–$300 range depending on finishes, site conditions, and island-specific material costs.

Meaningful property value uplift. Properties with legal second dwelling units attract a wider buyer pool and command premium pricing. Studies cited by Hawaii construction professionals suggest that well-built ADUs can contribute a 20–30% increase in market value, making the construction cost a compelling investment rather than just an expense.

Cash flow in a high-demand rental market. Hawaii's rental vacancy rates remain among the lowest in the country. An ADU creates a second income stream from the same property—directly offsetting mortgage costs or building toward long-term passive income.

Flexibility over time. An ADU can serve different purposes across its lifespan: a long-term rental now, housing for a family member later, or a home office in between. That adaptability adds functional value beyond pure financial return.

Important Restrictions Investors Should Know

ADUs are not a blank check. Several important rules govern how they can be used—and investors who overlook them can find themselves in regulatory trouble.

Short-term rental restrictions on Oahu. The City and County of Honolulu's ADU program was designed to expand long-term rental supply, not vacation rentals. On Oahu, ADUs cannot legally be used as short-term rentals (such as Airbnb or VRBO). Units must be rented for a minimum of six months. Investors looking to operate vacation rentals should explore a separate conditional use permit process, which carries additional requirements.

Owner-occupancy requirement (Oahu). Current Oahu rules require the landowner or a family member to reside on the property—either in the main home or the ADU—after construction is complete. This is a meaningful restriction for non-owner-occupant investors and should factor into any acquisition analysis.

HOA and covenant restrictions. Planned master communities with Homeowners Associations—particularly in areas like Ewa Beach—may prohibit ADU construction entirely. Act 39 does restrict covenants from limiting ADUs below state law for properties in urban districts, but it's worth conducting a title search before proceeding.

One ADU per lot cap (Oahu). Under current Oahu rules, only one ADU per lot is permitted—a contrast with the Big Island's allowance of up to three under Bill 123. This may evolve as the county updates its ordinance ahead of the Act 39 compliance deadline.

Infrastructure requirements. Water, sewer, electrical capacity, and drainage systems all need to meet code. Older neighborhoods may require upgrades before an ADU can be approved, adding to the project budget.

How to Finance an ADU Project in Hawaii

Construction financing for an ADU project requires capital structured differently from a standard acquisition loan. Traditional banks often move slowly and may not accommodate the phased nature of a construction project—a significant drawback in Hawaii's competitive market, where timing matters.

This is where a private money lender like JVB Capital Solutions offers real advantages.

JVB's Drawdown Loans are purpose-built for construction projects. Rather than releasing the full loan amount upfront, funds are disbursed in stages as construction progresses through defined milestones. Borrowers only pay interest on the amount drawn—not the total loan—which makes cash management more efficient throughout the build. As each phase is completed, supported by documentation like invoices and receipts, the next draw is released.

For investors who have already completed an ADU and are waiting to refinance into long-term financing or sell, JVB's Bridge Loans provide short- to mid-term coverage with loan-to-value options up to 75% ARV and terms up to 24 months.

Unlike conventional lenders, JVB's underwriting focuses on the property's value and potential—not just the borrower's credit profile. That translates to faster approvals and more flexible structuring, allowing investors to move with confidence on time-sensitive projects.

Is an ADU the Right Move for Your Investment Strategy?

ADUs represent a compelling opportunity for the right investor in the right situation. Act 39 has opened doors that were previously closed, and county-level legislation like Bill 123 on the Big Island signals a broader shift toward density and housing flexibility across the islands.

That said, success with an ADU investment depends on knowing the rules specific to your island and zone, building costs into your numbers honestly, and securing financing that matches the timeline and structure of a construction project.

At JVB Capital Solutions, we work with investors across Oahu and beyond to ensure they have the capital to move quickly and complete projects on their terms. If you are exploring an ADU project and want to understand your financing options, get pre-qualified today and speak with our team about a loan structure that fits your goals.

Frequently Asked Questions About ADUs in Hawaii

What did Hawaii's Act 39 (SB 3202) require counties to do?

Act 39, signed by Governor Green on May 28, 2024, requires all Hawaii counties to adopt or amend their ordinances by December 31, 2026, to allow at least two ADUs on all residentially zoned lots. It also prohibits private covenants from restricting ADU construction below the amount permitted by state law.

What is Bill 123 and which island does it apply to?

Bill 123 is a Hawaii County (Big Island) ordinance signed by Mayor Roth that implements—and expands upon—the state's ADU mandate. It allows up to three ADUs per property in residential and agricultural districts, caps each ADU at 1,250 square feet, and allows one unit per property to be used as a short-term vacation rental.

Can I use an ADU as an Airbnb on Oahu?

No. The Oahu ADU program is specifically designed to increase long-term rental supply. ADUs on Oahu must be rented for a minimum of six months and cannot legally operate as short-term vacation rentals without a separate conditional use permit. Violating this rule can result in fines and enforcement action from the City and County of Honolulu.

How much does it cost to build an ADU in Hawaii?

Construction costs in Hawaii generally range from $200 to $400 per square foot, with most projects averaging $250–$300 per square foot. Final costs vary depending on unit size, design complexity, finishes, site conditions, required utility upgrades, and island-specific material and labor pricing.

What is a Drawdown Loan and is it useful for ADU construction?

A Drawdown Loan is a type of construction financing where funds are released in stages as a project hits defined milestones, rather than all at once. Borrowers only pay interest on the amount drawn at any given time. This structure aligns naturally with ADU construction, where costs are incurred progressively. JVB Capital Solutions offers Drawdown Loans specifically for Hawaii real estate development projects.

Do I have to live on the property to build an ADU on Oahu?

Under current Oahu rules, yes. The landowner or a family member must reside on the property—either in the main home or the ADU—following construction. This is an important consideration for non-owner-occupant investors evaluating an ADU strategy on Oahu.