I agree with Fred, if you insulate you end up having moisture issues in the winter if you don't have ventilation...I had a bird bath heater in my chicken's water, and at 0 to -10, it vaporized and got my chickens all wet. I took the water out, put in dry bedding, and started just giving them fresh cold water twice a day. We have just a plywood coop, out of the wind, and other than that vaporized water episode, we have never lost a banty polish, game, or Leghorn, or any standard Red Stars or Polish. I use Christmas tree lights in a jar to heat the coop - it is just a little heat, not warm in any way. We live in the "mitten" above you, about 25 miles west of Lake Michigan and 30 minutes from Milwaukee..