var scrollTop;
var maxTop;
var bottom;

$(function(){
	maxTop = $('#banner_raum').offset().top;
	var timer = setInterval(elevate, 100);
});

function elevate(){
	bottom = $(document).height() - $('#banner_raum').outerHeight() - $('#ft').outerHeight();
	if ( scrollTop != $(document).scrollTop()) {
		scrollTop = $(document).scrollTop();
		destination = ( scrollTop > maxTop ) ? scrollTop : maxTop;
		destination = (destination < bottom) ? destination : bottom;
		$('#banner_raum').queue([]).animate({ top: destination + 'px' }, 500);
	}
}