Garage conversion rules in Honolulu County, HI — sometimes called garage-to-ADU or accessory living unit conversions — govern permits, ceiling height, egress, and parking replacement.
Converting a garage into living space on Oahu is typically treated as creating an ADU under ROH Sec. 21-5.720, requiring a building permit under Sec. 18-3.2 and compliance with parking, setback, and occupancy rules.
Honolulu County regulates garage-to-living-space conversions under the accessory dwelling unit framework in ROH Sec. 21-5.720 when the converted space includes kitchen and bathroom facilities. A separate building permit under ROH Sec. 18-3.2 is required for the structural and occupancy change. Parking lost to conversion must usually be replaced elsewhere on the lot. For conversions built without permits before September 14, 2015, after-the-fact permit provisions allow legalization if standards are met. The conversion counts as the one ADU allowed per zoning lot and must satisfy rental-term and advertising restrictions.
Unpermitted conversions, missing replacement parking, or operating a second unit beyond the one-ADU limit may trigger stop-work orders, civil fines, and required restoration.
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See how Honolulu County's garage conversions rules stack up against other locations.
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