Our winters are rather mild. Perhaps 2 weeks of total freeze, and maybe a week of nights in the teens?
Through all that time, my birds sleep outside in their run under tarps.... I can certainly say that it is drafty if there are winds, but I've never had them frost bit. However, others I know with enclosed walls on their coops did end up with frost bite. This will be my first winter with my new coop with walls. But the entire top edge under the roof is open, we'll see how the birds do.
We don't get -20's, we probably have not had even single digit temps in a long time, so if that is the case where you are, I don't think you can have too much ventilation.
Through all that time, my birds sleep outside in their run under tarps.... I can certainly say that it is drafty if there are winds, but I've never had them frost bit. However, others I know with enclosed walls on their coops did end up with frost bite. This will be my first winter with my new coop with walls. But the entire top edge under the roof is open, we'll see how the birds do.
We don't get -20's, we probably have not had even single digit temps in a long time, so if that is the case where you are, I don't think you can have too much ventilation.