With a vertical hive, you can increase volume by adding space above (supering) or below (nadiring). Conventionally, supers are added when the hive is crowded and ready to store honey in earnest, which they always do above their brood, to make use of the warm air rising to evaporate water from their nectar. Multiple supers can be added in a productive season, with various systems on offer for shuffling the filled and empty boxes for maximum yield. Nadiring is used mostly in the Warré system, which uses a single box size for both brood and honey, to allow downward expansion of the brood nest, which in turns gives bees the opportunity to back-fill the space that becomes vacant above them as adult bees emerge from their cells. Because nadiring requires all the boxes in a hive to be lifted simultaneously - in order to maintain nest atmosphere - some form of mechanical lift is generally used for the purpose, to avoid hernias and slipped discs. To avoid excessive lifting, most Warré beekeepers will nadir in spring with the number of boxes they expect to be filled by the end of the season. Some Warré beekeepers use a combination of nadiring and supering: nadiring in spring for downward expansion, while supering at the beginning of a flow to maximize honey crops.