We Need a little more air!
The horizontal hive pictured here seemed to need more ventilation because the bees were heavily gathered at the entrance and were "bearding" on hot days. We decided to solve the problem by drilling a hole in the top on both the front and the back. Yes, my son wore a bee suit when he drilled the holes! He did use a handbrace though, so it was quieter and it didn't seem to bother the bees very much. We weren't sure if we would need to do this at some point, so my son had drilled holes inside before it was populated with bees in the rafter in the middle, so the air can flow all the way through. We put a metal disc over the hole, which can be turned to close the hole, or to ventilate it but with too small of holes for bees to fly through. We have it full open right now. The day we did it was hot, so it was a good test. It seemed to really help. This hive gets more sun than my other horizontal hive. The other hive also has a flat roof and is double walled. It has not had the problem with "bearding".