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
We do not yet publish a verified Honolulu ordinance summary. Use this page for a planning-level cost estimate, then check Honolulu's planning or building department for rules that apply to your parcel.
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.