The front yard shall be a minimum of twenty-five (25') feet provided, however, that where an established building line exists closer than twenty-five (25') feet to the street line, then the front yard can conform to the established front yard setback within the same block. In those blocks where the established front yard is greater than twenty-five (25') feet, new construction within the fifty (50') feet of an existing building may be placed no more than five (5') feet closer to the front property line than the existing building, but in no event shall any new construction under this provision be nearer to the twenty-five (25') feet from the street line.