I have a short parapet wall which I do not know how to detail. The wall is 12″ tall and above a double top plate. The flat roof is covered with 3/4″ advantech, the parapet wall with 1/2″ advantech. The roof WRB (vapor permeable) is continuous with parapet wall WRB and then with external wall WRB. I will place 4″ rockwool (top rock DD) on the flat roof that will then go up the parapet wall and be continuous with the insulation on the external surface of the wall. 

When I think about it now, however, that parapet wall cavity is not connected to anything. Should I leave it be (as suggested by the building science website) or create ventilation holes to the outside (as suggested by hammer&hand website)? 

I attached a photo prior to the placement of the sheathing and WRB. Thank you very much for your help.