A slatted rack is not considered an essential component of a standard hive, however, we do favor these and think that they will help with your hive tremendously especially if your hives are located in northern regions where the weather tends to go from extreme cold to extreme warm throughout the seasons.
The basic functions of a slatted rack are to add additional cluster space for less congestion at the bottom of the hive and also to help with extra ventilation. Generally, bees will gnaw on the bottom portion of the wax comb of the frames nearest to the bottom board which makes it impossible for the queen to lay eggs there. They do this to protect the health of the cluster from extreme temperature variations. In the winter, a slatted rack keeps the brood chamber warmer so that the queen can lay eggs all the way to the bottom of the lowest frames. In spring and summer when the colony populations are the largest, a slatted rack provides extra cluster space again by allowing the queen to lay eggs lower which in turn can reduce swarming. They are placed in between the bottom board and the bottom brood box and can be left in the hive all year long. The slats run perpendicular to the entrance of the hive.
Our slatted racks are made of strong, sturdy pine. They come unassembled with complete instructions and nails. We recommend painting the exterior for added protection from the weather. They measure 20” long by 16.25” wide and can only be used on 10-frame hives.