Every single vent spot in my coop is adjustable. That means the windows on the south, west, and east sides. That means the vent on the north side. That means the vents at the top of the walls. That means the mobile home exhaust fan above the people door. That means the pop door between the coop and the run. That means every opening in my uninsulated, unheated coop can be closed against the high winds we get with our winter storms but left open on the downwind sides. Nothing is ever closed completely. In fact, the only time anything is closed is when we get our howling winter winds, usually from the north. Then only that side is closed, but even then it's left open a crack unless snow is blowing in. The hardware cloth covered openings between the rafters and the walls, up at the tippy top of the coop are the exception. They are left open all year round.
We do cover our hoop style run with greenhouse plastic in the winter. The chickens can't be left confined in a coop during those long, dark days of winter. Their entrance into the run is a covered "tunnel" - basically a three sided box. This is great for air flow without draft. Because it has a 90 degree angle they have to navigate to get in and out, winds can't blow directly into it but air from the slightly warmer run can flow through it. And they aren't stuck in the coop waiting for me to let them out in the morning. The run is usually several degrees warmer than the coop and it has a lot of boredom busters in it. The result is that we have had no frostbite issues*, no humidity or ammonia buildup, and no feather picking or gang wars.
I got into a bit of an exchange with JackE regarding insulation last year when we were at the beginning of the coop build. He was right and I was wrong. If I'd insulated that coop as heavily as I planned to initially, we'd have had so much humidity built up in there that I would have been the cause of problems for my chickens, not the solution.
* A clarification is necessary here. We did have a broody hatched chick who got frostbite. The week he was hatched it was in the upper 60s. Kids were out in their Halloween costumes with no jackets! Within 26 hours we had plummeted to 17 below during the day and even colder at night. Scout got frostbitten feet from a little bit of water that leaked out of the waterer nipples, probably as he was drinking, and his feet froze. No amount of insulation, no diligence by mom, nothing would have prevented what happened to him, nor healed him. As it is he lived to become the stumpy footed king of the coop!
