Honolulu allows ADUs and Ohana units in residential zones with minimum 3,500 sq ft lot size. Size varies by lot size (400 sq ft for 3,500-4,999 sf; 800 sq ft for 5,000+ sf). Owner/family member must live on-site. Complex permitting.
Zoning & Size Requirements [1]
| Allowed Zones | R-3.5, R-5, R-7.5, R-10, R-20; Country Districts (AG-1, AG-2) |
| Max Size (Detached) | 400 sq ft (3,500-4,999 sf lot); 800 sq ft (5,000+ sf lot) |
| Max Size (Attached) | Same size limits as detached |
| Max Size (JADU) | N/A (Hawaii calls these Ohana units) |
| Max Height | Not specified; standard building codes apply |
| Max Units | 1 ADU + 1 Ohana unit possible on larger lots (7,500+ sf); Ordinance 25-2 allows 2 units on all lots |
Setback Requirements [1]
| Rear Setback | Standard building code requirements |
| Side Setback | Standard building code requirements |
| Front Setback | Standard building code requirements |
| Parking Required | 1 space minimum (2 for Ohana units); exempt if within 1/2 mile rail transit |
| Owner Occupancy | Required - owner or family member must live on property (either main or ADU) |
| Min Lot Size | 3,500 sq ft minimum for ADU; varies for Ohana units |
Permit Process & Fees [2]
| Approval Process | Department of Planning and Permitting (DPP) approval required. Complex permitting with utility coordination. |
| Review Timeline | 90-120 days typical (longer than mainland due to complexity) |
| Permit Fees | $3,000-$8,000 estimated (higher utilities/inspection costs) |
| Impact Fees | Utility connection fees substantial; electrical panel upgrades $5,000-$15,000 |
| Plan Check | 4-6 weeks typical |
| Pre-Approved Plans | Limited pre-approved designs; custom plans more common |
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Construction Costs
| Average Build Cost | $150,000-$300,000 |
| Cost per Sq Ft | $250-$400 |
| Garage Conversion | $120,000-$200,000 |
| Prefab ADU (Installed) | $100,000-$150,000 |
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Rental Income Potential
| Avg Rent (1 Bedroom) | $1,600-$2,200 |
| Avg Rent (2 Bedroom) | $2,200-$3,000 |
| Short-Term Rental | Minimum 6-month lease; short-term discouraged to preserve neighborhood |
| Est. Annual ROI | 10-15 year payback due to high construction costs; strong rental income |
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Recent Law Changes
What's Changed Recently
- Ordinance 25-2 allows 1 ADU + 1 Ohana unit on same lot
- State law change (by 12/31/2026) may allow 2 ADUs on all residential lots
- Relaxed family occupancy rules for Ohana units
- Focus on affordable housing through ADU program
Tips for Building an ADU in Honolulu
- 3,500 sq ft minimum lot size is substantial barrier
- Utility connections expensive; plan for electrical/water upgrades
- Ohana units require family member occupancy only
- Six-month minimum lease discourages short-term rentals
- Verify zoning with DPP before purchasing property
Sources & References
All data on this page is sourced from official government records and verified market data. View our full methodology.
- Honolulu Planning Department — ADU Information Planning Department — Accessed 2026-03-15
- Honolulu Building Department — Permit Information building_dept — Accessed 2026-03-15
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