sharepoint resize verticle scroll

I am going to add a custom div in b/w ribbon and workspace div. I find the scrolling bug

HTML

<!-- ribbon -->
<div class="s4-pr s4-ribbonrowhidetitle" id="s4-ribbonrow" style="height: 44px;">
</div>
<!-- ribbon end -->

<!-- ribbon -->
<div id="s4-header">
  custom header
</div>
<!-- ribbon -->

<!-- ribbon -->
<div id="s4-workspace" style="height: 1045px; width: 1600px;">
</div>
<!-- ribbon -->

this is the structure of masterpage.

and I m using the following jquery script.

function FixWorkspace() {
  // if you are using a header that is affixed to the top (i.e. SharePoint Ribbon) put the ID or class here to change the workspace height accordingly.
  var header = '#s4-header';
  var width = $(window).width();
  var height;
  if ($(header).length) {
    height = $(window).height() - ($(header).height()+90);
  } else {
    height = $(window).height();
  }
  $('#s4-workspace').width(width).height(height);
}

$(document).ready(function() {
   FixWorkspace();
});

$(window).resize(function() {
   FixWorkspace();
});

on page load, this script works and set the height value but suddenly after some seconds it revert to default height value (i.e 1045px ). any help in this regards.