Adding that if a bird has impaired circulation as my late Delaware rooster, Isaac, did, from severe arthritis, they are more prone to frostbite in their feet, even if their combs are fine. He would occasionally fall off the roost because of his stiff hock joints, just lost his balance, and would not make it back up and would sleep on the floor. One winter, I was not aware he had fallen and he slept on the floor at 2* with wind chills way in the negative numbers. We had good bedding, but the coop was raised and air could blow under the coop. Isaac got frostbitten feet, though his comb was perfectly fine. That made me not think it was frostbite at first, never saw frostbitten feet on a bird of mine, and no one else had any issues. The coops were very dry with good high up ventilation. I know it was because of his bad circulation. He lost two toe ends though we doctored him up and took care of him, but he did okay after that.
Our barn now is directly on the ground with raised floor inside, so no wind underneath at all. We have five windows, two on the high weather side and three on the opposite side that are always cracked, plus a roll up door on one end that has a 2" x 6' gap at the top that, of course, is always open due to the structure of the door.