Ill try to stay as far away from the science as possible. LOL Ill also preface by saying that in normal circumstances (lower 48) you don't need to insulate.
In your situation I would strongly advise on insulation though. Part of the reason being that you will def. need a small heat source when it stays below freezing for that long of a period of time. If you do add a heat source (no matter how small) you will create a great deal of condensation inside if you are not insulated. We usually say that it is not the cold that is the enemy, but the moisture combined with the cold. You unfortunately have both problems and will amplify one problem when you try to solve the other. You therefore are going to be forced to deal with both at the same time. My advice would be to heavily insulate and very strategically place ventilation as high as possible so the warmer air in the coop carries out the moisture without sacrificing too much heat. Basically get your heat source low and below the roost and keep your vents as high and away from the roost as possible.
This way the only air movement you have moving past the hens is warm, but yet it should still carry the moisture up and away. As long as you stay with electric heat (convection and infrared) it is a dry heat. Versus gas heat which is moist (besides the safety concerns in a coop)
Edited by bairo - 4/7/12 at 7:47pm