1 family converted into 2 family

[Lillian Arroyo]

Hi!! 
I’m a new investor currently  looking to buy a house that is a one family but the previous owner converted it into a two family so his mother could live downstairs.  The first floor needs some updating but the upstairs needs to be gutted because they had a roof leak years ago.  So my question , do I have to file an application with zoning for it to pass inspection bc the owners never filed anything pertaining to converting it or will it pass and be  grandfathered in as a two family?