I would like to fade my nav

I would like to fade my nav

Hi,

Since 1 hour i would like to fade my navbar when i scroll down but it doesnt work 

this is my root code:


<script type="text/javascript" charset="utf-8">
      $(function() {
          $('.navbar').hide();
      });

      $(window).scroll(function(){  
            posScroll = $(document).scrollTop();  
            if(posScroll >=1080)  
            $('.navbar').slideDown(450).fadeTo("slow", 0.5);  
          else  
            $('.navbar').slideUp(450);
                    
        });

    </script>


Thank you for your answers