Patio fences may be erected in rear yards only, to a height of six feet (or average of six feet for stepped fencing) extending a maximum of 10 feet from the rear wall of the original building parallel to and along the party lot line of duplex houses. Such fence may be of wood materials, pierced masonry or ornamental iron providing not less than 10% daylight openings. In the case of a stepped fence, no portion shall be higher than the bottom of the facia board of original construction and the highest point will be adjacent to the building.