What is an ADU on the Big Island?

On Hawaiʻi Island, ADUs are commonly discussed as ʻohana dwelling units or additional dwelling units depending on context. The allowed pathway and requirements depend on zoning, site conditions, and the County's permit process.

Is there a minimum site size requirement for an ʻohana dwelling unit?

Hawaiʻi County's zoning text for ʻohana dwellings includes a minimum building site area of 10,000 sq ft for a site containing both the first dwelling and the ʻohana dwelling unit.

Do ʻohana dwelling units have special height or yard rules?

The ʻohana dwelling division includes a 25-foot height cap for detached ʻohana units (with a duplex/common-wall exception) and requires detached ʻohana units to meet the zoning district yard requirements plus an additional five feet.

How long does the ʻohana dwelling permit decision take?

The ʻohana dwelling permit process references a decision window after application acceptance (typically 30–60 days) for approval/denial within that division's procedure.

Building on Big Island

ADU Construction on Hawaiʻi Island

Permits, zoning basics, and build support for ʻohana dwelling units and ADU-style projects.

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Back to Building on Big Island Tiny Homes

If you're considering an ADU or ʻohana unit on your property, you're in good company—many Big Island homeowners are exploring the same path. Hawaiʻi County has specific rules that often differ from the mainland, and it pays to understand the practical path before you spend on design.

Below we walk through permits, zoning basics, and what to plan for so you can make informed decisions and avoid costly surprises.

What this page covers

Compliance path

How ADU-style builds are typically handled under Hawaiʻi County zoning and permits, including ʻohana dwelling rules.

Build planning

Site constraints, utilities, and design decisions that impact cost and approval time on the Big Island.

Big Island ADU rules: the practical version

Important:

Zoning and land use on Hawaiʻi Island are governed through the County's zoning framework (County Code Chapter 25). For site-specific answers, the County Planning Department is the authority.

Minimum building site area: 10,000 sq ft for a site containing both the primary dwelling and the ʻohana unit.
Detached yard requirements: Detached ʻohana units must meet the zoning district yard requirements plus an additional 5 feet.
Height: Detached ʻohana unit height limit is 25 feet, with an exception when configured as a duplex/common-wall.
Process timing: The ʻohana permit procedure references a decision window after acceptance (30–60 days).

These points come from the ʻohana dwelling unit division within Hawaiʻi County's zoning text. Verify with the County Planning zoning and land-use reference hub.

Permit pathway

Most compliant builds follow a standard sequence:

Feasibility check: zoning district, lot size, setbacks, access, and utilities.
Concept design: footprint, height, ingress/egress, parking implications.
Permit set: building plans, site plan, and any required engineering.
County review + permit issuance: timelines depend on completeness and site complexity.
Construction + inspections: phased inspections through completion.

If you want us to do the feasibility pass, send your TMK (or address) and a rough program: size, detached vs attached, and intended use.

Design decisions that affect cost and approval speed

Utilities

Water: county service vs catchment
Waste: sewer vs septic capacity
Power: panel capacity, new service, trenching

Site + climate

Grading and drainage
Corrosion exposure near coast
Wind exposure and roof detailing

How we help

Feasibility + compliance check
Plan coordination (designer/engineer as needed)
Permit-ready construction planning
Build execution with inspection readiness

Talk to a Builder

ADU planning can feel overwhelming, but verifying feasibility early is the smart move. If you have a TMK or address and a rough idea of size and use, we can help you understand whether an ʻohana or ADU pathway is realistic before you invest in design.

Reach out and we'll walk through the next steps with you.

Related guides

FAQ

Can I build an ʻohana unit on my property?

It depends on zoning district, site size, yard requirements, and infrastructure capacity. We verify feasibility before any design spend.

What's the minimum building site area?

The ʻohana dwelling unit division includes 10,000 sq ft minimum site area for a site with both dwellings.

Do detached ʻohana units have stricter yards?

Yes, detached ʻohana units must meet the district yard requirements plus an additional five feet.