barra fixa quando a rolagem escondê-la

fix-header.css

body.fixed-header .header-container{
  position: fixed;
  /*... Outros Css para barra fixa aqui*/
}

fix-header.js

jQuery(function($){
        var targetSelector = '.header-container';//use your class or selector heare
        var fixedClassName = 'fixed-header';//nome da classe que será adicionada no body, ver css abaixo
        var $header = $(targetSelector);
             
        var wrapperClass = $header.attr('class').replace(/\s/,'_') + '-wrapper';

        var $wraper = $('<div/>').addClass(wrapperClass);
        $header.wrap($wraper);
        var barSize = $header.height();
        $wraper = $('.' + wrapperClass);
        
        
        var $window = $(window);        

        
        $window.scroll(function(evt){
            var breakpoint = $window.scrollTop() - (barSize  + 100);
            if (breakpoint > 0){                
                if(! $(document.body).hasClass(fixedClassName)){
                    $wraper.css('height',barSize);
                    $(document.body).addClass(fixedClassName);
                }               
            } else {
                if( $(document.body).hasClass(fixedClassName)){
                    $wraper.css('height','auto')
                    $(document.body).removeClass(fixedClassName);
                }
            }
        });
    });