M Brennen
Songster
It may have been that cold when the frost bite occurred. It wasn’t all of them, just a few. It doesn’t seem to get moist in the coop In the coldest winter months. I have the worst time during the spring thaw and trying to clean the coop.Floor height nests are fine but I wouldn't have them right under the roost unless you're putting poop boards overhead to protect from... splatter.
Frostbite is moisture + cold. By "closing it up tight" you're causing moisture to build up in the coop, which can worsen frostbite. Hence why it's important in most climates to have ample ventilation available year round.
Obviously if you're talking -25F or more then yes the cold itself becomes a concern.