You can set position: fixed; on the div you want to have maximum height, and then set its height to 100%. I created a quick fiddle where you can see it in action.
HTML:
<div class="row"> <div class="small-4 columns" id="sidebar"> Fixed full height </div> <div class="small-8 columns"> Other Content </div> </div>
CSS:
#sidebar{ position: fixed; height: 100%; background: #222; color: #FFF; padding: 5px; }
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