Heat and water
Like Lnorris, I too insulated my coop slightly when it was built. I added a thin layer of insulation and some tar paper to prevent wind getting in. My coop's door for the chickens is at the lowest level of the coop so that any cold air that enters stays below the chicken roosts higher placed higher up.
An IR heat bulb is placed high in the coop for heat. I don't bother with a thermostat control. I have a heating plate that keeps their water in a liquid state. During the day, the chickens will walk to the hoop house/green house where they can scratch and 'dirt bath' when the sun is out. I almost always throw some scratch grain in the hoop house along with any table scraps in there as well. A hand full of sand or two helps with digestion.
One more thing. The door to the hoop house is removed for Winter. I then cover most of the entry with a large piece of carpet leaving a chicken crawl space below. When the chickens want in, they just duck under that carpet and then hop up about 3 inches into the hoop house, Works like a treat as they say.
I have the 'ribs' reinforced via 2×4 center support stretched from one end to the other with a 4×4 post in the center for any snow/ice load. I brush that off when I get to it after clearing the driveway and house.
This is just what I've done for my New England chicks having experienced -25 degF for two weeks ages ago. Those cold fronts do come down hard, and when they do they have a tendency to overstay their welcome.