Scroll to top gist

scroll-to-top.js

// calculating some values
var header_height = $('.header').outerHeight(),
  scroll_top_icon = $('#scroll-to-top'),
  scrollTop = $(window).scrollTop();

// Scroll to top function 1/2
$(function(){
  $(window).scroll(function(){
    if( scrollTop > header_height ){
        scroll_top_icon.fadeIn();
    } else {
        scroll_top_icon.fadeOut();
    }
  });   
});

// Scroll to top function 2/2
scroll_top_icon.click(function(){
  var body = $("html, body");
  body.animate({scrollTop:0}, '500', 'swing');
});

scroll-to-top.scss

#scroll-to-top{
	position: fixed;
	z-index: 100;
	bottom:15px;
	right:15px;
	display:none;
	background-color: rgba(255,255,255,0.8);
	@include transition();
	@include rotate( $val: 180deg );
	&:hover{
		cursor:pointer;
	}
	.icon-ajmn-download{
		display:block;
		padding:0;
		margin:0;
		color:$color-accent;
		font-size:2em;
		text-align:center;
		&:before{
			float: left; //this is a bit of a hack
			padding:5px;
		}
	}
}

srcoll-to-top.html

<div id="scroll-to-top"><span class="icon icon-ajmn-download"></span></div>