Every building, other than a building on a corner lot, in a Residence C District shall set back from each side lot line at least 15 feet, if an apartment house or hotel, and at least 10 feet, if a one-family dwelling, two-family dwelling or other permitted use, except that, any accessory building, all part of which are over 60 feet from any street line, may set back not less than three feet from a side lot line other than a street line.