listen(window,'load',stretchLayout);

function stretchLayout() {
   var header = elemById('header');
   var content = elemById('contentcolumn');

   var winHeight = measure('window').y;
   var siteHeight = elemById('site').offsetHeight;

   if (siteHeight < winHeight) {
      content.style.height = winHeight - header.offsetHeight + 'px';
   }
}