Ventilated gabled cover or “vestibule box” with slotted inner cover is one piece of beekeeping equipment over looked and is needed to effectively deal with excessive moisture found in more temperate climates. Warm air holds moisture, and the warmer the air, the more moisture it can hold. Since a beehive is loaded with moisture from both bee respiration or drying nectar, the hive can quickly become a damp, mold-infested environment that is not healthy for bees.
Winter is particularly problematic in a cold hive where the bees’ activity warms the air immediately around the cluster. This warmer air rises until it reaches the cold inner cover where the moisture condenses, often dripping back down on the bees. In either case—winter or summer—the faster you can get rid of moist air, the better.
The ventilated gabled roofs or vestibule boxes with slotted inner cover provides a double whammy to moisture-laden air. First, the ventilated space provides a place for this air to collect that is well above the supers. Secondly, the vented space gives the air a way to escape. The extra height provided by the gable or vestibule is important because the greater the distance between the inlet and the outlet, the better the draft.
You can forget about follower boards for ventilation unless the hive cluster needs to be reduced. If you need additional ventilation during the summer months just stagger back the supers as per our cover picture. You get better ventilation, a second defensible entry for busy foragers, and you have one less piece of non-productive equipment in your hive. The vestibule box also becomes a “capping s’ feeding station” after you have extracted the surplus honey supers.
The other benefit of the slotted inner cover, in of itself , is you can use the slots to “peek” into your hive on those days when everyone tells you “your bees will turn to stone” if you observe your bees after “Labor Day and before Valentines Day”… white pants and formal attire not required.