I suggest you read this article. It's a sticky and was written by a lady in Ontario so she should have some credibility when it comes to cold weather. I'll throw in her ventilation article too as lagniappe.
Pat’s Big Ol' Ventilation Page
https://www.backyardchickens.com/web/viewblog.php?id=1642-VENTILATION
Pat’s Cold Coop (winter design) page:
https://www.backyardchickens.com/web/viewblog.php?id=1642-winter-coop-temperatures
A few things I'd like to add. We all have different conditions, different coops, different birds, and different management techniques. There is seldom one and only one right answer for each and every one of us. A large walk-in coop built on the ground is a lot different than a small elevated coop.
The biggest danger from cold is frostbite, not them freezing to death. Frostbite can occur at any temperature below freezing, but moisture in the air is a huge factor. The more moist the air, the higher the danger of frostbite. Wind chill is a factor too. You need a well-ventilated coop to get the moisture out. There have been many posts on here where people have solved frostbite problems by providing more ventilation in the cold weather. You don't want a small tight coop that keeps the moisture in. You want a well-ventilated coop to get the moisture out.
There is also an ammonia issue. Ammonia is generated from their poop and is really hard on their respiratory system. If the poop is frozen or dry you are not going to get much ammonia, but if it thaws and is wet, it can generate a bunch. Ammonia is quite a bit lighter than air. You need a good vent over their heads when they are sleeping to get rid of the ammonia.
Something to consider on the size of the coop. In really cold climates there are going to be days that the chickens don't want to leave the coop. It might be snow on the ground or it might be a blowing blizzard. With them stuck in too small a coop for days on end, they can get bored and develop real behavioral problems, sometimes fatal behavioral problems.
It is really rare for a chicken to freeze to death. It can happen, but I really believe that chicken was weak to start with: sick, injured, infected something that made her susceptible and the stress from the extreme cold pushed her over the edge.
I really worry about providing heat in the coop for a couple of reasons. One is the fire danger. The other is them not being used to the cold so a power failure can be a real bad problem, maybe even fatal to them. I really don’t think I’d be doing my chickens any favors by getting them used to the extra heat. But if you feel you must provide heat, there are less risky ways to do it.
Instead of something that gets hot enough to start a fire, use a heat source that does not get hot enough to start a fire. Most of us have a lot of really flammable material in the coop. Use a ceramic heater or maybe an oil filled radiator set on low. There are still risks with the electricity in the coop, but a lot less than with a heat lamp.
I really think Pat’s articles should be required reading for anybody building a coop in colder weather. They are really good.
On the insulation issue. To me the big advantage of insulation is in the summer. Insulation can really reduce the heat in the coop if it is under the roof or on the sunny side. In the winter to protect against the cold the advantage is less obvious and less effective. But even with really good ventilation, good insulation can greatly reduce the rate of cooldown, especially if you have thermal mass in there providing some warming.
Pat’s Big Ol' Ventilation Page
https://www.backyardchickens.com/web/viewblog.php?id=1642-VENTILATION
Pat’s Cold Coop (winter design) page:
https://www.backyardchickens.com/web/viewblog.php?id=1642-winter-coop-temperatures
A few things I'd like to add. We all have different conditions, different coops, different birds, and different management techniques. There is seldom one and only one right answer for each and every one of us. A large walk-in coop built on the ground is a lot different than a small elevated coop.
The biggest danger from cold is frostbite, not them freezing to death. Frostbite can occur at any temperature below freezing, but moisture in the air is a huge factor. The more moist the air, the higher the danger of frostbite. Wind chill is a factor too. You need a well-ventilated coop to get the moisture out. There have been many posts on here where people have solved frostbite problems by providing more ventilation in the cold weather. You don't want a small tight coop that keeps the moisture in. You want a well-ventilated coop to get the moisture out.
There is also an ammonia issue. Ammonia is generated from their poop and is really hard on their respiratory system. If the poop is frozen or dry you are not going to get much ammonia, but if it thaws and is wet, it can generate a bunch. Ammonia is quite a bit lighter than air. You need a good vent over their heads when they are sleeping to get rid of the ammonia.
Something to consider on the size of the coop. In really cold climates there are going to be days that the chickens don't want to leave the coop. It might be snow on the ground or it might be a blowing blizzard. With them stuck in too small a coop for days on end, they can get bored and develop real behavioral problems, sometimes fatal behavioral problems.
It is really rare for a chicken to freeze to death. It can happen, but I really believe that chicken was weak to start with: sick, injured, infected something that made her susceptible and the stress from the extreme cold pushed her over the edge.
I really worry about providing heat in the coop for a couple of reasons. One is the fire danger. The other is them not being used to the cold so a power failure can be a real bad problem, maybe even fatal to them. I really don’t think I’d be doing my chickens any favors by getting them used to the extra heat. But if you feel you must provide heat, there are less risky ways to do it.
Instead of something that gets hot enough to start a fire, use a heat source that does not get hot enough to start a fire. Most of us have a lot of really flammable material in the coop. Use a ceramic heater or maybe an oil filled radiator set on low. There are still risks with the electricity in the coop, but a lot less than with a heat lamp.
I really think Pat’s articles should be required reading for anybody building a coop in colder weather. They are really good.
On the insulation issue. To me the big advantage of insulation is in the summer. Insulation can really reduce the heat in the coop if it is under the roof or on the sunny side. In the winter to protect against the cold the advantage is less obvious and less effective. But even with really good ventilation, good insulation can greatly reduce the rate of cooldown, especially if you have thermal mass in there providing some warming.
