Poly hive designs available in the U.K. and Ireland
Poly hives are available in a number of different national designs in Europe, but in the UK there are only really two types available - Langstroth and the British National. Within each type different frames sizes are available as they are with wooden hives, such as Jumbo Langstroth and National 14 x 12.
Langstroth shallow supers can catch out the unwary, as being mostly of European origin they are not made to the same standard as the most common shallow Langstroth in the UK. Poly Langstroth supers will often use frames 6.25" deep, which is a size known in the UK as Dadant Shallow, but elsewhere as Medium or Three Quarter Langstroth. This is not a major issue providing the right sized frames are purchased, as Dadant Shallow frames are widely available in the UK.
Poly hives are available from a number of different suppliers and their products differ in detail although there are also similarities. It is not the intention of this article to draw attention to specific features of any particular hive, as personal preference will play a part as much as practical considerations. The choice of hive design must be decided first, but from a financial point of view the beekeeper would be wise not to dismiss the Langstroth as quickly as they might if deciding only between wooden hives. This is because in poly terms the Langstroth is by far the most numerous and given the very high costs of tooling for a new poly hive, Langstroth hives do currently potentially offer significantly better value for money compared to the current British National designs - which cannot of course be sold anywhere outside the UK.
There is one other design feature which is worth mentioning, this is the compatibility or otherwise of a particular poly hive design with the equivalent wooden components. This is a subject where opinions can be strongly divided. Those with a significant number of wooden hives may wish to retain compatibility, but for those starting from the outset of their beekeeping with poly, or those with only a few wooden hives, compatibility is likely to be less significant compared to other factors. However, it is worth mentioning that all current designs (2012) of poly hive in the UK are sufficiently compatible for operations such as a Bailey frame change or the uniting of colonies with newspaper. It is only where the prolonged mixing of say wooden and poly supers is required on the same colony that issues can arrive with some designs. However, the main benefit of poly hives is the thermal insulation they offer the colony - so the addition of wooden components can only degrade this and this is why the beekeeper changing to poly is recommended not to mix wooden and poly components except for short periods.
A typical poly hive will have a varroa floor, brood and shallow supers with sides approximately 40mm thick and a flat roof. Crown boards of the type so common in wooden hives, normally consisting of a framed ply board, usually with holes for bee escapes, are not used with poly hives. For poly hives the use only of some sort of inner cover consisting either of a piece of clear rigid plastic or simply a piece of thick polythene sheeting (approx. 500+ microns thick) is most often encountered. Not all beekeepers use an inner cover but when they are used the purpose of it is simply to prevent the bees sticking the roof down with propolis which makes it hard to remove without overly disturbing the bees. With a plastic sheet the roof can be lifted off easily and then the sheet can simply be peeled back gently from one corner. With a rigid plastic inner cover the hive tool can be used to prise up a corner which is then grasped in the hand and lifted off.
Unlike with wooden hives, which normally have a heavy roof, the roof of poly hives is very light and needs to be held in place. This is usually done with a strap, weight on the roof or in some hive designs, metal clips. The advantage of a strap is it can go round the complete hive and even secure it to the hive stand for extra stability in strong winds. A large rock is quick to use but will mark the roof in time.