I am not sure why but it seems to be every Manhattanites’ (myself included)dream to buy their neighbor’s apartment and combine the two. According to NYTimes, there may be some basic considerations to mull over. I would add that it’s a good idea to do an analysis with the costs to combine of your contractor/architect and see if it might not make more sense to just sell your current Manhattan pad and buy a bigger apartment given the inconvenience of either moving out or living through construction.