Side forms shall be of lumber of not less than two (2) inches nominal thickness or steel of equal rigidity. The minimum depth of the side forms shall be equal to the sidewalk thickness. No two (2) inch by four (4) inch lumber forms shall be permitted. Forms shall be held securely in place by stakes or braces with the top edge true to line and grade. The forms for sidewalk shall be set so that the slab will have a fall of one (1) inch vertical to four (4) feet horizontal from the edge nearest the property line toward the edge farthest from the property line, except as may be otherwise directed by the Department of Code Enforcement.