Beespace is the gap between any two components inside a bee hive that is not either filled with wax comb or sealed with propolis to provide no access. All modern hives recognise the importance of beespace in their design. The normal figure given for beespace is between 6mm and 8mm and the frames in every hive are designed so that this gap exists all around the frame.
The sides of the frame are one beespace from the side of the hive and there is one beespace between the top of any box and the next box above it. Beespace is an essential component in the design of any removable frame hive. If this is not maintained between every part of the hive the bees will stick the components with propolis and build wild comb in gaps that make it difficult to inspect the colony without damaging the comb and annoying the bees.
When considering various hive designs it will become apparent that some are described as 'top beespace' and others as 'bottom beespace'. This is because the internal components of the hive must retain beespace whilst the outer box must be 'bee tight' with no gaps.
Top beespace designs result in a 6-8mm gap between the frames in the box and the top edge of the box, whereas bottom beespace designs have the frames and the top of the box flush, with beespace provided at the bottom of the box. The many debates about which is best that suggests that there is little difference between the two. For a new beekeeper it is better to use top or bottom beespace as dictated by the hive design chosen.
Beespace is approximately the height of an adult bee. By preserving beespace throughout the hive bees are able to visit all areas and ensure the colony is kept clean and that any predators are unable to find a safe haven in odd corners. It is interesting to note that there is one place were the gap between two components is twice beespace and this is between adjacent frames holding brood. This is because the workers need to tend the brood and it is necessary for workers to work 'back to back' in this area
Excerpt from the book: The bbka guide to beekeeping