Jquery Scrolling div - Prevent from entering site footer

Question

I have a side menu on my site that i would like always visible.
To accomplish this, I am using the following code sample from this page:

http://camwebdesign.com/

Answer 1

Demo

http://jsfiddle.net/NsfwM/

fullscreen http://jsfiddle.net/NsfwM/embedded/result/

JS

var $scrollingDiv = $("#scrollingDiv");

$(window).scroll(function(){            
    var y = $(this).scrollTop(),
        maxY = $('#footer').offset().top,
        scrollHeight = $scrollingDiv.height();

    if(y< maxY-scrollHeight ){
        $scrollingDiv
        .stop()
        .animate({"marginTop": ($(window).scrollTop()) + "px"}, "slow" );        
    }    
});

And another with your 30px offset in place http://jsfiddle.net/NsfwM/1/