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Maui Property Owners Can Now Build Two ADUs: Assess Infrastructure & Water Constraints Now

·10 min read·⚡ Act Now

Executive Summary

Maui County's updated ordinance, effective since July 2026, permits up to two Accessory Dwelling Units (ADUs) on many residential lots, aligning with state law. Real estate owners and investors should verify specific lot eligibility and assess local infrastructure and water availability before proceeding with development plans. Investors should also watch for potential shifts in rental market dynamics and construction viability.

  • Real Estate Owners: Expanded ADU potential on eligible lots, but site-specific constraints need evaluation.
  • Investors: New opportunities in ADU development and rental markets, contingent on buildability.
  • Small Business Operators: Potential slight increase in demand for construction services.
  • Action: Real estate owners should immediately review lot eligibility and consult with local planning departments regarding infrastructure and water availability.

Action Required

High PriorityOngoing, but immediate planning is advised

The ordinance is already in effect, and property owners can begin planning or acting on new ADU construction, potentially missing out on timely development if they delay.

Real estate owners should immediately verify lot eligibility for up to two ADUs and consult with the Maui County Department of Planning and Board of Water Supply regarding infrastructure and water availability before proceeding with development plans. Investors must conduct thorough due diligence on buildability and market demand.

Who's Affected
Real Estate OwnersInvestorsSmall Business Operators
Ripple Effects
  • →Increased ADU construction → increased demand on water resources → potential for higher water costs or restrictions for all users.
  • →Utility infrastructure strain → need for costly public upgrades → potential for increased taxes or utility fees.
  • →Expanded rental supply → subtle shifts in labor availability → potential impact on housing affordability for service workers.
  • →Development pace vs. infrastructure capacity → localized service strain → impact on quality of life and business competitiveness.
Aerial shot of beachfront houses surrounded by lush greenery in Kihei, Hawaii.
Photo by Griffin Wooldridge

The Change

Maui County has enacted an ordinance allowing for the construction of up to two Accessory Dwelling Units (ADUs) on a single-family residential lot, a significant expansion of previous regulations. This change, which took effect in July 2026, is in alignment with a broader 2024 state law aimed at increasing housing supply across Hawaii. The ordinance broadens the scope of properties eligible for ADU development, potentially unlocking new housing stock and investment opportunities.

However, the practical application of this ordinance is subject to existing local requirements. Developers and property owners must still navigate stipulations related to parking, essential infrastructure capacity (sewer, electrical, roads), and critically, water availability. These factors may significantly limit the actual number of ADUs that can be feasibly built, even on eligible lots. Interested parties are advised to verify specific lot compliance and consult with Maui County planning and water departments.

Who's Affected

Real Estate Owners

Property owners, landlords, and developers stand to benefit most directly from this ordinance. The ability to construct two ADUs on a single lot increases the potential return on investment for properties in eligible zones. This could lead to increased rental income, greater property value, and more diverse housing options. However, the feasibility hinges on site-specific constraints. Owners must confirm their lot meets all zoning, dimensional, and infrastructure requirements, particularly the capacity for water service and wastewater disposal. The process may involve navigating complex permitting and potentially requiring upgrades to existing utilities, which can add significant costs and timelines.

Investors

For real estate investors, this presents an opportunity to diversify portfolios with new ADU development projects or to acquire properties with enhanced income potential. The increased flexibility in ADU construction could spur new niche development companies or attract capital to existing ones focusing on these smaller-scale residential units. However, investors must conduct thorough due diligence. The viability of ADU projects will depend heavily on local market demand, construction costs, and the availability of essential resources like water. Investment strategies may need to account for longer development cycles and potential regulatory hurdles related to infrastructure capacity. The long-term impact on the rental market, potentially increasing supply and moderating rent growth in some areas, also warrants monitoring.

Small Business Operators

While not directly involved in ADU development or ownership, small businesses, particularly those in the construction and skilled trades sectors, may see a modest increase in demand. Plumbers, electricians, general contractors, and material suppliers could experience a boost in project volume as property owners begin to pursue ADU construction. Businesses that can scale their services or specialize in ADU development and renovation may find new revenue streams. However, the overall economic impact will depend on the pace of ADU construction and any concurrent slowdowns in other development sectors.

Second-Order Effects

The expansion of ADU allowances on Maui, while intended to increase housing supply, can have cascading effects within the island's constrained economy. Expanded ADU construction could increase demand for water resources, potentially straining already limited supplies and leading to higher water utility costs or restrictions for all residents and businesses. This increased demand on infrastructure, if not adequately managed, could also necessitate costly public utility upgrades, which may be passed on to taxpayers or utility users, impacting the operating costs for all sectors. Furthermore, an increase in rental units, even small ones, could subtly shift labor availability dynamics, potentially impacting housing affordability for essential workers in sectors like hospitality and retail. If ADU development outpaces infrastructure upgrades, it could lead to localized strains on services, impacting the quality of life and potentially the competitiveness of Maui as a visitor destination or a place for businesses to operate.

What to Do

Real Estate Owners and Developers

  1. Verify Eligibility Immediately: As soon as possible within the next 30 days, identify specific properties that may qualify for one or two ADUs under the new ordinance. Consult the Maui County Department of Planning Land Use Division for the most current zoning maps and ADU regulations.
  2. Assess Site Constraints: Within 60 days, conduct preliminary assessments for each eligible property regarding parking requirements, setbacks, lot coverage, and importantly, the capacity for utility connections, particularly water and sewer. Engage with utility providers (e.g., Board of Water Supply) for service availability and potential upgrade costs.
  3. Consult Professionals: Within 90 days, engage architects, engineers, and contractors experienced in ADU construction on Maui. Obtain detailed cost estimates that factor in potential infrastructure upgrade expenses and the time required for permitting.
  4. Navigate Permitting: Begin the permitting process as soon as feasible. Understand that permitting timelines can be substantial, especially if infrastructure assessments or upgrades are required. Proactive engagement with the county planning department is crucial.

Investors

  1. Market Analysis: Within the next 60 days, analyze current rental market trends on Maui, focusing on demand for smaller rental units and potential rent ceilings for ADUs. Assess the local construction market for ADU feasibility and cost-effectiveness.
  2. Due Diligence on Development Viability: For any potential ADU development projects, conduct rigorous due diligence on the underlying real estate, focusing on the physical capacity for ADUs and associated utility hookups. This should align with the site constraint assessments undertaken by real estate owners.
  3. Strategic Portfolio Review: Within 90 days, evaluate how increased ADU supply might impact existing rental portfolios and consider opportunities for new ADU-focused investments. Monitor the pace of ADU development and its impact on neighborhood amenities and infrastructure strain.

Small Business Operators (Construction & Related Services)

  1. Capacity Assessment: Within the next 30 days, evaluate your business's capacity to take on additional projects, including potential ADU construction. Identify any need for specialized training or additional staffing.
  2. Business Development: Begin outreach to real estate professionals and developers to inform them of your services relevant to ADU construction. Develop standardized service packages or pricing for common ADU configurations.
  3. Monitor Demand: Continuously monitor county planning department permit applications for ADUs to gauge market demand and project pipeline. Adjust marketing and resource allocation accordingly.

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