No permit to erect or maintain an elevated sidewalk shall be granted except where a railroad switch or spur track is situated along and adjacent to the curb line of a sidewalk and within five (5) feet thereof, or upon or along the portion of a cul-de-sac between the closed end thereof and the first street intersecting such cul-de-sac on the same side thereof on which it is desired to construct such elevated sidewalk. No such elevated sidewalk shall be more than three (3) feet in height, and before any work or construction of any elevated sidewalk is done the complete plans and specifications thereof shall be submitted to the Board for approval.