@aart I've had the same questions regarding ventilation. I know I'm not doing something right because the first winter we had some frostbitten combs. Last winter was better, but I still don't think I'm getting it right. Would you be willing to take a look at my coop, (I'm pretty sure you can see the photos from my profile page or whatever it's called.) The windows are at the level of the chickens' heads. Other than the door and cracks along the top, bottom and edges of the rear doors, there is no other ventilation. The roosts are about a foot away from the wall but I'm not sure their heads are low enough below the roof. Thanks in advance.