I thought that might be it. They don’t understand how chickens (or wild birds that overwinter) stay warm. They wear a down coat, those things are extremely warm.
I don’t know where you are across the state line from me, but we don’t get winters all that cold as far as chickens go. I occasionally get a bit below zero Fahrenheit, but only by a few degrees. Some chickens sleep in trees in our climate during the winter and do fine as long as they are fairly sheltered from the wind.
What chickens in our climate need to keep themselves warm is good ventilation and protection from direct winds. An easy way to do that in a tall coop is to have openings in winter above their heads when on the roost. That way any breezes are over their heads. Some people get fancy with roof vents or gable vents but I just have overhang and leave the top of the walls open (covered with hardware cloth against predators). That keeps the worse of the rain and snow out and lets bad air be exchanged for good air.
Chickens trap air in their feathers and down. Those tiny pockets of air provide great natural insulation. If a wind strong enough to ruffle their feathers hits them, they can lose those pockets of air. Light drafts of air are fine, it’s a breeze that ruffles feathers that needs to be avoided.
Your heat in summer is going to be much more dangerous to your birds than cold in your winter. Heat kills a lot more chickens than cold. If your chickens are relatively healthy and have a minimum of protection that can handle cold. In our summers you can’t have too much ventilation. Open windows with wire coverings for predator protection are very helpful. I have an area down at the bottom on the cool side of my coop that I open during summer. I can block that in winter.
To me the only reason to insulate a coop in our climate is to provide some protection against heat in the summer. I don’t have it in my coop, it’s not necessary, summer or winter. But it won’t hurt as long as you have good ventilation and it’s not a kind they can eat. They will eat ventilation and it is not good for them. Depending on what kind it is you may need to cover it.
I took this photo when it was four degrees above zero Fahrenheit a few years back. I left the pop door open and they decided to come out. If a cold wind had been blowing they would not be out like this. They really can handle cold weather quite well.
