Yes, I was not trying to say people further north never have frostbite. Anytime you have freezing weather there is a risk for frostbite. People in pretty warm climates where it barely gets below freezing can create conditions they can cause frostbite. People in Canada and Alaska can create conditions where single combed chickens do not or practically never suffer from frostbite. Anytime and anywhere it gets below freezing there is a risk.
As with anything else it’s not one simple thing, it’s a combination of things. Comb and wattle size and shape can make a difference. Roosters are normally more at risk than hens because combs and especially wattles can get pretty large comparatively. There are some modifiers that can make a single comb fairly small. There are modifiers that can make even pea and rose combs weird-shaped, the Vee shape gene for example. My mixed breed EE’s with one pea comb gene can get some pretty funky shaped combs. Thin pointed parts of the comb are more at risk than thicker or more rounded parts. In general comb type can affect the risk of frostbite to the comb. It doesn’t help the wattles risk. All in all my personal opinion is that comb type is a fairly small factor but it is a factor and some people need all the help they can get because of other factors.
Moisture is a big factor. You will practically never get the moisture level inside the coop lower than the moisture level in the air outside. I say practically because here are always exceptions to what anyone says on here. For most of us the cold snaps that concern us normally come with drier air, which helps. That’s why it’s often too cold to snow, the cold air just doesn’t have the moisture to make snow. But there are conditions where the outside moisture is fairly high and it is below freezing. The best you can do is provide enough ventilation to get the moisture content inside to approximate the moisture level outside.
In addition to their breathing water that is not frozen, such as heated water, can be a big moisture source. They need to drink water so what are you going to do? If it’s cold enough, their poop will soon freeze so that’s not a big moisture source until it thaws. Hopefully by then it’s above freezing so the danger from frostbite is past, but the ammonia smell may crank up.
Condensation from the moisture in the air usually isn’t a big problem once it gets well below freezing, it just freezes on the wall and stays frozen until it warms up. Right at or above freezing when the coop material, especially metal, cools off faster than the air you can get a lot of moisture in the coop. One way that can thaw and release a lot of moisture while the air is still below freezing is if the wall is hit by the sun and warms up. Using wood instead of metal can really help with condensation. Some people insulate their roof because of condensation.
You often see on here to keep drafts away from the chickens. When people see the word “draft” they think of holding a candle near a house window or door to see I there is any air coming in. That’s not the type of draft that’s a concern. You need some air movement to exchange good air for bad. That kind of air movement is good. What you want to avoid is a breeze hitting them. Wind chill is a real effect as far as frostbite goes. The higher the moisture in the air and the faster the wind the more effect it has. Gentle air movement is good, a breeze is bad. Another reason you don’t want a breeze hitting them is that they keep themselves warm by trapping tiny pockets of air in their down and feathers. Those tiny pockets of air provide great insulation. If a breeze strong enough to ruffle their feathers hits them, those tiny air pockets can be released and they lose that insulating effect. That can lead to dead chickens.
Frostbite doesn’t just affect their comb and wattles, it can affect their feet. There is a lot of debate on this forum about what shape of roosts to use, 2x4’s flat, 2x4’s on edge, or round roosts like tree limbs. I’ve experimented with all three and found that height and location in the coop are the determining factors where they will sleep, not the shape of the roost. The chickens just don’t care. And when mine squat down on the roosts to sleep and fluff their feathers to keep themselves warm when it is really cold, their feet disappear under those feathers. Their feet are covered no matter what the roost shape is. You can get some pretty passionate people on here telling you why one way is better than the other on all sides of that question. I’m like my chickens, I just don’t care which you use, they all work for me.
What is much more important to me than shape of the roost is the material it is made from. Metal and most plastics are really good conductors, they can conduct heat away from the bird’s feet and lead to frostbite. Wood is a good insulator, it is pretty lousy when it comes to conducting heat. The chickens can quickly warm that area of the roost so it stays warm. To me roosts need to be made from wood.
To me there are several different ways to get the small air movement you need to get moisture out of the coop. What you are trying to achieve is enough movement to get the air out but not hit them with a breeze. The Woods Coop is one design that works well. There are different factors involved with that. I have not looked at the design in detail since I manage mine a different way. I don’t know how important that bump-out is but I suspect it is important since it adds some complexity to the build. Why make the build harder if there is no benefit. Maybe putting a droppings board under the roosts and pretty close to the roosts will help deflect any breezes that might make their way inside. Vertical baffles can help as long as it doesn’t create new roosting spots.
To me the simplest way in winter to get good winter ventilation without having a breeze hit them on the roosts is to have openings above their heads. Any breeze will pass over them but still cause a bit of turbulence to get the bad air moving outside. If it is dead calm outside you won’t get that turbulence but warm air rises and holds more moisture. It is usually warmer in the coop than the air outside from the birds’ body heat and breathing, from any thawed water when it is really cold out, poop before it freezes, and if the coop is on the ground the ground is usually warmer than the air in a cold snap. Gravity will push warm air up and force cool air in even with the openings up high. In summer those high openings along with another opening down low and on the shady side of the coop where the air is cooler will help keep the coop cool. I open a window also in summer. I used to have a link that showed sketches of air flow (passive conditions, no fans) for various designs for animal housing that showed the Woods concept and the concept of openings above their heads but that link no longer works and I haven’t been able to find what I want on another link.
A long post and there is certainly some opinion in here, but these are my thoughts if someone wants to greatly overthink this. I’m good at overthinking. Providing sufficient ventilation while preventing breezes hitting them doesn’t have to be all that complicated if you are building from scratch. Retrofitting can be more challenging. Building something tiny instead of providing adequate room can also complicate the design. I’m always in favor of providing more room for different reasons.
