The area of Parking Districts, when put to use for the parking of vehicles, or the loading and unloading thereof, shall be paved, adequately drained and adequately screened from the view of surrounding residential areas by a closed cleft wooden fence or evergreen plants, either of which shall be at least six feet in height, which said paving, draining and screening shall be effectively maintained at all times; and if lighting is provided, the same shall be so arranged as not to be objectionable to adjoining residential areas.