Change from 1 Family to 2 Family

We’re thinking of purchasing a brownstone in Park Slope and, after lurking here, I feel so much better educated about the whole process. I do, though, still have a few questions and I’m hoping some of you may be able to provide some guidance. Several of the properties we are considering are either 1 family homes or are “currently being used as a 2 family” or “currently being used as a 1 family with a professional office/tenant on the garden level.” We need a two family house, though we won’t be formally renting the garden level (there will be family living there). How difficult/costly (from a permit perspective, not a renovation perspective) is it to change from any of the above to a legal 2 family residence? If we are not formally renting the garden level apartment do we need to legally change to a 2 family (all the work will be done above board and permitted)?

By 1stitchwonder |