There is a good article in Back Yard Poultry about winter and chickens. It would be good for all to check it out. The author says even in the coldest times a roost is the only way to go. Just keep the coop draft free. I have a thermometer in my coop and as soon as I close the door at dark the temp raises 20+ degrees. The coldest it has ever gotten is 29 when it was 12 outside. Only 12 birds in a 6x8 coop.