Steps for working with City (Concord, NH) to add two more units

[Renee R.]

I'm in discussions with a seller to buy a duplex in Concord NH that has great space on the second and third floor of an attached double-bay over-sized garage to add two 1BR units. I'm looking for guidance to the steps to take BEFORE I buy to ensure that I would be able to do those additions. I don't want to get into a situation where I've bought the property and the city won't allow me to add the units. It's zoned RN. I own a 4-unit next door in IS zone. Any guidance is much appreciated.