chickens can handle pretty extreme cold if they are given protection from drafts, while at the same time provided ventilation and water that isn't frozen. with the hopes of keeping egg production up during winter, I provided insulation to the inner coop and made the door in the floor of the roosting area that is off the ground. I'm not sure how much it helps but if figure at the very least provides some comfort and helps them adjust to the wild swings in temperature we get here, crammed between two mountain ranges at sea level. the most significant thing I've found so far to effect egg production and I think overall quality of life for them is light. in the north here, the days get really short come December. I added three windows to the side of the roosting area and when I extended a run off the side, I covered it with translucent roofing. The girls seem to love having more light and their egg laying nearly doubled with in a few days.