In discussions with the ICC directly, their position is that a top railing is required. The reason is that the glass and its support system must meet a 200 lb concentrated or 50 lb/ft uniform load at the TOP by a safety factor of 4. This means that the bare edge of the tempered glass must be able to withstand an 800 lb concentrated load. 1/2″ monolithic tempered glass cannot withstand that load onedge.
You can view information on this at https://kb.wagnercompanies.com/?ht_kb=is-a-top-railing-required-for-glass-railinghttp://wagner.kayako.com/Knowledgebase/Article/View/159/22/is-a-top-railing-required
There was a change in the 2009 IBC which does allow for a glass railing without a top rail if laminated, tempered glass is used. You will need to confirm with local jurisdiction in Kentucky to see if they are on the 2009 code or if they will accept it for this job. We do have experience in this application. Most notably a glass railing for Amway Arena in Orlando which used 9/16″ laminated Sentry Glass in our PanelGrip system.
We can provide you with the test report on this if you would like.
We do also have a clear polycarbonate cap rail that you could use if 1/2″ monolithic is the way you need to go.