Can You Build an ADU in Honolulu?
ADU rules in Honolulu are set by local zoning in Hawaii. Many Hawaii cities allow ADUs — here's what to check, plus typical costs ($218,500–$357,000 for a 700 sq ft detached unit).
Construction in Honolulu runs about 5% above the Hawaii average, so budget toward the higher end of these ranges.
Detached ADU (700 sq ft)
$218,500–$357,000
Garage conversion (400 sq ft)
$68,000–$124,500
Statewide protection
Local rules
What applies in Honolulu
Hawaii ADU (‘ohana unit) rules are set by each county. Honolulu allows one ADU on qualifying lots; check your county planning department for size and parking standards.
Check the Honolulu planning or building department for ADU size, setback and parking rules before you design.
Estimate your Honolulu ADU cost
Your property
ADU typeEstimated cost in Hawaii
$218,500 – $357,000
≈ $312–$510/sq ft turnkey · midpoint $288,000
- $195,900
- Construction
- $51,800
- Design & permits
- $40,300
- Site work
- iSize set locally. This state leaves ADU size limits to your city — typical caps run 600–1,200 sq ft. Check your local code.
- iParking. Set by local ordinance — commonly 1 space per ADU unless near transit.
- iOwner-occupancy varies. Owner-occupancy rules are set locally in this state.
- ✓Lot has room. A 700 sq ft ADU uses about 12% of your 6,000 sq ft lot — comfortably within typical coverage limits.
Rule basis: Local zoning governs — rules vary by city/county
If you rent it out
$1,450–$2,350
est. rent/mo
7.9%
gross yield
13.6 yrs
payback
~$21,204/yr after a 7% vacancy allowance, before financing & maintenance.
Financed over 20 yrs at 7.5%, the build is about $2,320/mo — vs ~$1,900/mo in estimated rent.
Estimates are for planning only and are based on regional construction-cost indices and published statewide ADU statutes. Local ordinances, lot conditions and contractor pricing vary — always confirm with your city planning department and a licensed contractor.
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Other Hawaii cities
Estimates are for planning only and are based on regional construction-cost indices and published statewide ADU statutes. Local ordinances, lot conditions and contractor pricing vary — always confirm with your city planning department and a licensed contractor.