You don't know what a draft is, in a coop. A draft is a cross breeze, that will ruffle the bird's feathers. This coop is built tight. No cracks in the corners, no gaps up by the roof. When the coop is in winter mode, with all the windows, and the entry door shut, there is no pathway in the coop for the wind to blow through. Even with the wide open front wall. I've had 35mph+ winter winds blow directly at the open front. You go inside the coop, and shut the door, it's as calm as it is in your living room watching TV. In the book, that is described as the air cushion effect. I get snow down here too, and no matter what it does, it never amounts to anything in the coop. Nothing ever worth worrying about.
If you were to have say, the eaves open, all the way around the coop, plus a ridge vent, I would bet that you would have more felt air movement in that coop, then mine. I'd bet $$$ on it. You would be providing that pathway through the coop. Could get drafty.
You keep chickens in a poorly ventilated box, with the misguided idea that by trapping "BodyHeat" you are doing them a favor. You are setting up a high humidity environment, combined with the cold, you will have frostbite, and probably respiratory issues. I've had winter temps to just below zero, not including any windchill, and I've ( Really, my chickens) NEVER had any problems what so ever, NONE.
Again, read the book
This is correct. In order for wind to move through, it must be replaced by more air. If there is no opening at the back of the coop, there is no way that air can move to the back of the coop where the roosts are because their is already a cushion, or pocket of air, there. The way a Woods coop is designed is to allow air movement through the front of the coop, therefore effectively displacing humidity, which is the bigger culprit for frostbite. Ask anyone who is a survivalist. Cold and wet equals disaster. There was a man on the news a couple years ago who was found wandering in freezing temps in the nude. He had gotten soaked and discarded his wet clothes in order to survive.
Air will flow in the path of least resistance. A woods coop and many other largely ventilated coops are well designed so that the uptake in wind never hit the roosting birds. Similarly in old houses, attic ventilation helps aid in removal of humidity without disturbing the air which resides in your living space. But if you've got a bad door fitting on one side of your house and a bad window jamb on the other, the air pulls through, creating an undesired draft. Completely different from the intended and well thought out ventilation system.