You really do have to guard against high humidity, so even if it's very very cold, you must have holes (covered against predators) high up above their heads so they won't get the draft . Chickens produce a lot of humidity via their breathing....and they still drink lots of water, too.
I am pretty new, too, and loving BYC. Welcome from northern-northern Minnesota!
When my coop was built I had a large vent cap put on the roof. Like a vent cap for a house. We never had any problems last year, the girls did well and no humid conditions inside the coop. We have ten birds now, the coop was enlarged so I hope the vent cap does well this winter.