Can You Build an ADU in Hilo?
ADU rules in Hilo are set by local zoning in Hawaii. Many Hawaii cities allow ADUs — here's what to check, plus typical costs ($208,000–$340,000 for a 700 sq ft detached unit).
Construction costs in Hilo track close to the Hawaii state average.
Detached ADU (700 sq ft)
$208,000–$340,000
Garage conversion (400 sq ft)
$65,000–$119,000
Statewide protection
Local rules
What applies in Hilo
We do not yet publish a verified Hilo ordinance summary. Use this page for a planning-level cost estimate, then check Hilo's planning or building department for rules that apply to your parcel.
Estimate your Hilo ADU cost
Your property
ADU typeEstimated cost in Hawaii
$208,000 – $340,000
≈ $297–$486/sq ft turnkey · midpoint $274,000
- $186,300
- Construction
- $49,300
- Design & permits
- $38,400
- 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
8.3%
gross yield
12.9 yrs
payback
~$21,204/yr after a 7% vacancy allowance, before financing & maintenance.
Financed over 20 yrs at 7.5%, the build is about $2,207/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.