Honolulu’s Department of Planning and Permitting FAQ describes a limited ADU path tied to zoning district and lot area. It does not provide one dimensional envelope for all residential properties.
Local standards
The selected local standards are summarized in the Frequently Asked Questions — Additional Dwelling Unit. The FAQ lists eligible Residential districts R-3.5, R-5, R-7.5, R-10, and R-20, plus Country District lots, with a 3,500-square-foot minimum. It states a 400-square-foot maximum for lots from 3,500 through 4,999 square feet and 800 square feet for lots over 5,000 square feet. Its wording does not assign the exact 5,000-square-foot case to either band.
Confirm the applicable rule
Only one ADU is allowed under this path, and the FAQ says some other dwelling types on a lot, including an Ohana unit or guest house, can make it ineligible. Underlying LUO rules still apply. Some pre-ordinance legal structures may have a discretionary adjustment route; that is not an entitlement. Confirm the current code, lot area, existing units, infrastructure, and restrictions. Zoning measurements do not by themselves establish fire separation, building-code compliance, utility capacity, or permit approval. For shared measurement methods, see the setback and separation guide and floor-area guide.
