No building or part of building, other than the steps, eaves, and similar fixtures, shall extend nearer to the center line of the street or road than the distance specified. Where a front yard is required under this Ordinance, the depth of the required front yard shall be measured from the setback from center line so specified, instead of from the side line (property line) of the street or road. However, in no instance shall the above require placing a main building more than ten (10) feet back of the front main wall of an adjacent building already existing within (50) feet of, and on the same side of the street with, the building or part of the building to be erected.