The county of Kauai requires two off-street parking spaces for a single family home. The county zoning ordinance (CZO) regulates such matters, there are circumstances that modify this requirement (such as with elderly housing projects), but generally speaking, a single family detached dwelling unit is required to have two parking spaces off-street.
When off-street parking serves more than one dwelling unit, the parking spaces are to be paved. That brings us to ARU and ADU and their respective parking requirements.
Before purchasing a property with “ADU potential” or “ARU potential”, as often represented by seller’s or their agents, consider the parking.
If indeed, an ADU is permitted and built, it is to have two additional off-street parking spaces. If together with the original two spaces, and serving both units, then they are all to be paved. (Consult with the county directly to confirm if you are indeed facing such a situation.)
An ARU, whether detached or not, will require an additional parking space. The county will request a description of the existing two parking spaces and the additional off-street space to serve the ARU.
Always, check with the appropriate government agency to know clearly what requirements there are to develop your property, or the property of your desire.