Compare ADU zoning rules across 1 Hawaii cities. Average ADU score: 7.0/10.
Gathered from the 1 city below, with the bill or ordinance each one names. Statewide measures are listed once with the cities they reached, rather than repeated for each.
Statewide law sets a floor; the numbers that decide your project are local. Here is the spread across the 1 Hawaii city covered here, taken from each city's own ordinance rather than a state summary.
| Question | Across Hawaii |
|---|---|
| Are ADUs permitted? | 1 of 1 permit them. |
| Detached size cap | Median 500 sq ft, from 500 to 500 sq ft across the 1 cities publishing a numeric cap. |
| Owner-occupancy | Required in none of them. |
| Build cost | $150,000 to $450,000 depending on city and unit type. |
Recomputed whenever a city page changes, so this and the city pages below cannot disagree.
| City | Max Size | Setbacks | Permit Fees | Build Cost | 1BR Rent | Score |
|---|---|---|---|---|---|---|
| Honolulu | 1,000 sq ft of floor area on zoning lots of 5,000 sq ft or more; 500 sq ft on lots up to 4,999 sq ft (ROH § 21-5.50-3(a)(1)(B), Ordinance 25-2, effective September 30, 2025). A legally built accessory structure that predates September 14, 2015 may be converted and exceed the cap by zoning adjustment if the director finds the floor area cannot practicably be reduced (§ 21-2.140-1(n)) | 5 ft in R-3.5 through R-20 for a single-unit, two-unit or duplex dwelling and the ADU that shares its lot (Table 21-3.2); 8 ft in R-3.5 and 11 ft in R-5 to R-20 when the lot's floor area ratio exceeds 0.6 (§ 21-3.70-1(c)(3)(H)); 10 ft in the Country district (Table 21-3.1) | $0 for the ADU's plan review and building permit: ROH § 18-6.5 waives both fees for the creation of an accessory dwelling unit, extended through June 30, 2030 by Ordinance 25-12 (no waiver if work started without a permit). For scale, ROH 18-6.2 would otherwise charge $700 plus $10 per $1,000 of value above $100,000 (about $2,200 on a $250,000 job) plus a 20 percent plan-review fee. Grading, grubbing and stockpiling permit fees processed with an ADU permit are waived too (§ 18A-2.4). A zoning adjustment, if needed, costs $200 initial review plus $400 processing (DPP, November 2025) | $150,000-$450,000 | $2,000-$2,800/mo | 7/10 |
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