Building permits, zoning and septic rules in Honolulu County, Hawaii

Yes. The City and County of Honolulu requires a building permit for work covered by its building code under Revised Ordinances of Honolulu Chapter 18, and a separate building permit is generally required for each building or structure^1,10. Honolulu has adopted locally amended versions of the 2018 International Building, Residential and Existing Building codes¹¹. A one-story detached accessory building serving a Group R-3 occupancy may be permit-exempt when it is used for storage, tools, a playhouse or a similar purpose and its total floor area does not exceed 120 square feet¹. Hawaii's owner-builder license exemption is not a building-permit or inspection exemption, so an owner who builds personally still applies for the county permit and passes county inspections¹². Permitted work remains subject to inspection, including a final inspection before final occupancy¹⁰. A building cannot be occupied, or its occupancy classification changed, until the Department of Planning and Permitting issues a certificate of occupancy¹⁰. Qualifying nonresidential agricultural structures may be exempt from a building permit and certificate of occupancy, but the exemption has notice, land-use, floodplain and utility conditions^13,14.

On Oahu the City and County's Department of Planning and Permitting handles building permits, and its Customer Service Division reviews and issues building permits for single-family and two-family homes, duplexes, and their accessory structures⁴. Reach the department at 650 South King Street, Honolulu, HI 96813, and call (808) 768-8220 specifically for residential building permits⁴. You can apply for an Instant Online Permit for many eligible single-family projects, or submit a full Internet Building Permit Application and receive an IBP number for projects that need plan review through the One-Stop Permit Center or Electronic Plan Review¹. Permit fees are based on your project's fair-market labor and materials value rather than a flat schedule, so use the department's online fee calculator to estimate cost before you apply¹. Septic permits do not come from this office; they come from the state Department of Health, covered below³.

Yes. Chapter 21 of the Revised Ordinances of Honolulu, the Land Use Ordinance, establishes zoning districts and precincts, allowed uses and structures, and zone-change procedures across Honolulu County². The Department of Planning and Permitting's Land Use Permits Division administers the county's local zoning as well as shoreline and Special Management Area rules⁴. Every parcel also lies in a state Urban, Rural, Agricultural or Conservation land-use district⁷. Rural-district residential lots generally require one-half acre, subject to state and county exceptions¹⁵. The housing code requires at least one living-purpose room with 120 square feet; most other habitable rooms must have at least 70 square feet, while an efficiency dwelling has separate requirements⁸. Lot size, setbacks and building height vary by district, and residential zoning lots on Oahu are limited to 75 percent impervious surface, which counts paved areas and driveways as well as roofs¹. Dividing or consolidating land requires subdivision review by the department^1,16.

The Hawaii Department of Health Wastewater Branch permits septic and other individual wastewater systems for Honolulu County properties that are not served by sewer³. Reach its Oahu/main office at 2827 Waimano Home Road, Ste 207, Pearl City, HI 96782, or (808) 586-4294³. A licensed engineer must perform the percolation test, survey the property and submit plans to the Wastewater Branch, and the filing fee is $100 for a new system or $25 for an addition or modification⁹. No one may use the system until the director authorizes it in writing⁹. An individual system generally is limited to 1,000 gallons per day and five bedrooms, and dwelling developments generally need 10,000 square feet of land per system, subject to stated exceptions⁹. Composting and incinerator toilets treat toilet waste only, so shower and kitchen wastewater still needs approved treatment and disposal⁹. New cesspools are banned, and existing cesspools must be converted to an approved system by 2050¹⁷.

We could not confirm a Honolulu County rule that generally allows long-term RV living, private-land camping or a tiny home as a separate dwelling, so ask the Land Use Permits Division about the parcel and proposed use before buying⁴. Honolulu's Housing Code treats a stationary trailer, powered vehicle or recreational vehicle used for living as a building, and living in a vehicle not designed for living is a public nuisance; the code does not authorize RV occupancy in every zoning district¹⁸. Hawaii law limits habitation in a vehicle on public roads and requires the property owner's or occupant's authorization for both parking and habitation on private property, while allowing county ordinances to supersede that state rule¹⁹. A tiny home used as a dwelling still faces Honolulu's building-permit and zoning rules plus approved sewer or wastewater service^4,9,10. A pre-manufactured or mobile unit may serve as an accessory dwelling unit on a qualifying Residential or Country District lot if it meets the accessory-dwelling rules and applicable building codes¹. Agricultural land leased under the state subdivision provision cannot contain permanent or temporary dwellings, trailers or campers²⁰. Short-term rentals of less than 30 days are allowed only in resort-zoned and other eligible areas, and each unit must be registered¹.

1. Confirm the parcel's county zoning district and state land-use district with the Land Use Permits Division, including whether the proposal needs subdivision review^4,7,16.
2. If you will act as your own general contractor, register for Hawaii's owner-builder exemption, supervise the work and arrange licensed electrical and plumbing work; selling or leasing within one year after final inspection can create a presumption that the project was built for sale⁶.
3. Apply through the Department of Planning and Permitting's Customer Service Division, using an Instant Online Permit if eligible or the Internet Building Permit Application and plan review process otherwise^1,4.
4. Determine sewer availability; a municipal connection that increases sewage flow may require a Sewer Capacity Analysis, while an unsewered property needs state approval for its individual wastewater system^1,9.
5. Obtain a well construction and pump installation permit from the Hawaii Commission on Water Resource Management if the project includes a well²¹.
6. Complete required building and wastewater inspections, then obtain the certificate of occupancy and written approval to use the wastewater system before moving in^9,10.

Identify the parcel's county zoning district and state Urban, Rural, Agricultural or Conservation district before assuming a home or accessory use is allowed^2,7. If Agricultural land is being offered through a lease subdivision, verify dwelling rights because the state provision can bar houses, trailers and campers on the leased area²⁰. Check flood status early: property in a flood zone cannot use the Instant Online Permit path, and flood-hazard construction plans must show the applicable flood boundaries, elevations and proposed lowest-floor elevation¹⁰. Confirm legal access as well; work for a residential driveway inside a state highway right-of-way requires a state permit²². Budget carefully for wastewater because only about 13.1% of Honolulu County soils are rated without severe limitations for a conventional septic drain field²³. If the property has a cesspool, include conversion by 2050 in the budget¹⁷.