The short answer is YES. You are required to have a 2 Unit License as well as a valid Certificate of Occupancy stating the use as a 2 Family Flat.
If you do not have a Certificate of Occupancy or are unsure whether one exists, contact us so we can research whether or not there is a previous Certificate of Occupancy on file for your property. Should a previous Certificate of Occupancy be on file, you may apply for a change of ownership.
If a Certificate does not exist and assuming the property zoning allows for it, you would need to go through the formal conversion process. For this, we would recommend reading our article on How to Obtain A Certificate of Occupancy.