Zoning and Building permit

[Paris Naberschnig]

Looking into buying a property thats zoned A4 general residential. The property is currently a single family home but could easily be converted into a 3/1 duplex. Who with the city do I need to check with before making an offer or starting construction to make sure this is allowed? Basically what renovations require a building permit? I dont plan to add on to the house; simply build out a kitchen on one side.