All sidewalks shall be under the direction of the Service Director. The space between the property line and the curb line on each side of the paved roadway or curbed streets shall constitute the sidewalk. Upon unpaved streets, the sidewalk shall be the portion adjoining the property line on each side and shall have a width equal to one-fifth of the distance between property lines, but in no case shall the sidewalks be less than four feet in width except in streets or alleys of sixteen feet or less in width, where the sidewalk shall be two and one-half feet in width.