jQueryでサイドバーの一部を固定をしたい

以下のようにしたら固定はできたのですが、ヘッダを固定しているため、その分上の方が隠れてしまいます。
どこを変えたら良いのでしょうか？

javascript
1(function(jquery) {
2  jquery(document).ready(function() {
3    var main = jQuery('#main'); 
4    var side = jQuery('#side'); 
5    var wrapper = jQuery('#scrollbox');
6 
7if (main.length === 0 || side.length === 0 || wrapper.length === 0) {
8return;
9}
10 
11    var w = jquery(window);
12    var wrapperHeight = wrapper.outerHeight();
13    var wrapperTop = wrapper.offset().top;
14    var sideLeft = side.offset().left;
15 
16    var sideMargin = {
17      top: side.css('margin-top') ? side.css('margin-top') : 0,
18      right: side.css('margin-right') ? side.css('margin-right') : 0,
19      bottom: side.css('margin-bottom') ? side.css('margin-bottom') : 0,
20      left: side.css('margin-left') ? side.css('margin-left') : 0
21    };
22 
23    var winLeft;
24    var pos;
25 
26    var scrollAdjust = function() {
27      sideHeight = side.outerHeight();
28      mainHeight = main.outerHeight();
29      mainAbs = main.offset().top + mainHeight;
30      var winTop = w.scrollTop();
31      winLeft = w.scrollLeft();
32      var winHeight = w.height();
33      var nf = (winTop > wrapperTop) && (mainHeight > sideHeight) ? true : false;
34      pos = !nf ? 'static' : (winTop + wrapperHeight) > mainAbs ? 'absolute' : 'fixed';
35      if (pos === 'fixed') {
36        side.css({
37          position: pos,
38          top: '',
39          bottom: winHeight - wrapperHeight,
40          left: sideLeft - winLeft,
41          margin: 0
42        });
43 
44      } else if (pos === 'absolute') {
45        side.css({
46          position: pos,
47          top: mainAbs - sideHeight,
48          bottom: '',
49          left: sideLeft,
50          margin: 0
51        });
52 
53      } else {
54        side.css({
55          position: pos,
56          marginTop: sideMargin.top,
57          marginRight: sideMargin.right,
58          marginBottom: sideMargin.bottom,
59          marginLeft: sideMargin.left
60        });
61      }
62    };
63 
64    var resizeAdjust = function() {
65      side.css({
66        position:'static',
67        marginTop: sideMargin.top,
68        marginRight: sideMargin.right,
69        marginBottom: sideMargin.bottom,
70        marginLeft: sideMargin.left
71      });
72      sideLeft = side.offset().left;
73      winLeft = w.scrollLeft();
74      if (pos === 'fixed') {
75        side.css({
76          position: pos,
77          left: sideLeft - winLeft,
78          margin: 0
79        });
80 
81      } else if (pos === 'absolute') {
82        side.css({
83          position: pos,
84          left: sideLeft,
85          margin: 0
86        });
87      }
88    };
89    w.on('load', scrollAdjust);
90    w.on('scroll', scrollAdjust);
91    w.on('resize', resizeAdjust);
92  });
93})(jQuery);
94