There's been quite a bit of talk in my bee group about the importance of warm hives. There are some reasonable arguments. I haven't found an academic article to back up this view yet, but that may come in time.
The honey bee rears brood at 35C-36C. When the hive is cooler than that the nurse bees will warm the brood with their abdomens. This thermo-regulation assists the developing brood, presumably by enabling enzymatic reactions. Varroa are said to favour cooler brood conditions, but I have no evidence to offer for this.
What can be said is that an over-wintering colony requires stores to keep warm. Warmer hives will use less volume of stores and so be less likely to starve in the spring.
I offer 4 innovations to address the winter insulation issue:
1 An insulated roof
This is an idea borrowed from the Warre hives. I've taken a Nationa eke (dimensions 460mm x 460mm x 70mm) and stapled hessian to the inside so that it forms a pouch which sits on the frame tops. The cavity in the eke is filled with straw or sawdust. This sits on an optional queen excluder to ensure the bee space at the top. I hope that this insulation will reduce heat loss from the hive roof.
2. An extra wooden skin
Warre owners frequently comment about the thicker walls relative to the National box. My idea is to add external insulation using wood.
Take any thick plank - a scaffold board would be ideal. Cut it so that it forms a square jacket around the hive. Now drill through the ends and bolt through (images to follow when I get round to making this). Tighten it all up and... you have a thick walled hive.
3. A cardboard skin
As for the wooden skin, but using corrugated cardboard. The outer would have to be coated to make it waterproof. I suspect that Linseed Oil would do, but I haven't tried this.
4. A cylinder hive using National box
This is a relatively simple construction but needs a more complete blog post.
My aim is to try 1, 2 and 4 this winter. I'll only be trying this on 1 hive for each idea so I'll only be able to comment on aspects of construction, weathering, cost etc.