HOW TO HOUSE IN COLD AREAS
I'm here in the foothills of Maine and winter is not any more of an issue then over heating in the summer. I have a 4x8 chicken coop, one window that I plastic over, due to it being inside a shed, we tar paper the back side to prevent drafts, and shingled the front to insulate and protect it. Cover the window with plastic, it has a "porch" made from chicken wire, covered with clear plastic so on warm days its like a solar heater. Also we placed a 2 ft long plastic (used clear so light can make it through the door window, this plastic prevents the whole "heat" from wooshing out the door when you open it in the cold. Also, keep adding shavings to moist/dropping areas and let it build up in the winter months as this is insulation where its the coldest. With your roosts, make sure the girls middle toe does not stick out beneath their feathers (perch is wide/round enough), this is when toes get frozen. And last, feed "hot mash" each morning, feed corn, fatty foods (keeps their energy up and warm) and I give them warm water 2 and 3 times a day. (all you need of hot mash is 1 cup feed and equal hot (not boiling) helps them keep warm and laying. Oh ! we have 5 in the house and they faired exceptionally.
I am shocked at how many folks heat and insulate their coops. Chickens can dust up a place and can create a combustable area while using a heater of any kind (not saying you shouldn't, but its just one of my thoughts).