Slatted racks can serve several purposes:

• Ventilation - In the summer, bees will gather in the space provided by the slatted rack and fan their wings, providing air movement to ventilate the hive, some claim this allows them to dry honey faster and easier. In the winter, it provides an insulating dead air space below.
• Swarm Reduction - Provides extra space for bees to hang out in, reducing congestion in the hive potentially delaying swarming.
• Draft Reduction - The 3" wide plank at the front helps to reduce drafts and chilled brood.
• Reduces Bearding - The extra space and ventilation naturally reduce the need for bees to beard.

These are about 1 7/8" tall with a 3/4" void on the bottom, 3/4" thick slats, and then a 3/8" void on top.