Where off-street parking, loading or service areas are to be located adjacent to a lot in any residential zoning district and where such parking, loading or service areas are not entirely screened visually from such lot by an intervening building or structure, there shall be provided along the lot line a continuous planting screen at least six (6) feet in height. No such screen shall extend nearer to a street right-of-way line than the established building line of the adjoining residential lot.