Except for permitted driveways and walkways, all parts of any front yard or side yard which abut the street shall be landscaped with grass or plant material and shall not be covered by concrete, bituminous macadam or similar or artificial nonporous substances. The grass or planting area must be maintained in front side yards for a minimum distance of eight feet from the back line of a sidewalk, with the exception that one side yard may have a driveway with a width not to exceed eight feet leading to the back yard parking area or garage(s).