All of the roosters in the large coop have signs of frostbite again. I left the windows open this year since only 3 birds out there are bantams. The standards and guinea fowl handle even the negative temperatures fine so in an attempt to lessen humidity this year I kept it open. They still all ended up with black combs. It's an old grain bin. 170 sq ft with a top vent, all wood, and definitely no bottom drafts. It's built so well that despite nearly 50 years of use when I rinsed it out the first summer it held water for the first 10". I had to drain it back out and dry the wooden floor. I would say it's just our weather but all the bantams I moved to the new little coop are fine despite some spilled water and no windows just a top vent. Proof that coop design not weather results in frostbite. Although I don't know the exact reason the large coop gets frostbite. The small coop doesn't stay warmer unless I run a space heater and I would think the humidity would be higher with the same amount of water in a smaller space. My humidity gauge in the large coop got lost so I can't confirm that. The grain bin works great in summer and looked like a great potential coop when I set it up but for one reason or another it just doesn't work in winter. This is the 2nd year they've all gotten frostbite and the biggest rooster has a swollen toe.