Convert a single family into a duplex

[Wesley Clark]

Hello Everyone, I am analyzing my first deal and think I have a great opportunity. My seller has a four bedroom single family house that they desperately want to get rid of. New roof, new furnace, newer windows. The house looks and like a duplex, has two identical sides (2 br / 1 ba ea). They have been renting it out as a duplex but legally it is a single address. What is the process / cost to legally make this a side by side? Utilities are not sub metered. One half is vacant and needs new flooring, dry wall and paint. The other unit is occupied and renting for $750/m but could use similar upgrades and demand a higher rent. House was just appraised for $160k. Any advise on how to make it legally a duplex would be awesome!