Adding a unit (and address) to a multi in Jax FL

[Garrett Masiulis]

I am under contract to purchase a multi in Jax. The property currently has two units, each in its own building, and each separately metered. I am looking to convert a 3 car garage to another unit in one of the buildings (already has extra kitchen and bathroom). I walked the property with a contractor and understand a permit will need to be pulled for the work but one thing we weren't completely sure about was adding an address to the building. Do I do this through the post office or the city?