This time of year, many poultry keepers drag out the heaters, cover the coop in plastic, and batten down the hatches with the goal of keeping their chickens warm and preventing frostbite. However, the effect is just the opposite. By not allowing the chickens to become naturally accustomed to the dropping temperatures, we undermine the chickens’ health. Becoming gradually accustomed is preferable to the shock of going from warm, inside air to cold, outside air. Chickens do not sweat or pee: A huge amount of water is expelled in their breath and through their moist droppings. Frostbite, along with respiratory illness which is so common in chickens, most frequently results from cold, damp air trapped in the coop.
Chickens do not actually need protection from the cold except in the most extreme of climates. Birds are better at adapting to cold than mammals. “Birds have more resistance to the cold weather than mammals. Their bodies are covered with feathers which insulate them by trapping warmed air. One technique that conserves heat is puffing out these feathers to act as an insulating coat,” (Pendergast, 2009). Their legs have only a thin layer of flesh which actually allows less heat to escape, and their beaks are horn. Birds can warm their legs by sitting upon them or pulling them up into their feathers and often roost together for warmth. During cold weather, birds keep their metabolism high to stay warm and may need to eat more.
Chickens do need protection from drafts and damp. These can be provided by careful planning. Make sure that you have one square foot of ventilation per chicken preferably above the roost level. If you keep the winter ventilation on one side of the coop and close down the other sides for winter, then the warm, moist air will rise out of the coop and the air within the coop will be fresh, dry, still, and warmer than the outside air.
Open-air poultry coops were designed in the 1800s and popularized by Prince T. Woods’ 1912 “Open-Air Poultry Houses for All Climates: A Practical Book on Modern Common Sense Poultry Housing for Beginners and Veterans in Poultry Keeping. What to Build and How to Do It. Houses That Will Promote Heath, Vigor, and Vitality in Breeding and Laying Stock,” which is available on Internet Archive. Then, as now, chicken keepers recognized the benefits of fresh air but were concerned about frostbite and precipitation.
We all know the difference between working in an open shed in winter and working in a cold, tightly closed building. The open shed is by far the most comfortable, for the cold is “drier,” the air is purer and more wholesome, and there is none of the depressing effect of the cold and chilling, stale, damp air. For the same reasons the open-front house is more comfortable for poultry than a closed house.
Admitting that the open-front house is more comfortable than a closed one, some poultrymen are still afraid to use it without curtains for fear of frosted combs and that storms will drive snow and rain into the building. These fears are not sustained by the facts shown in actual experience. Where cold, driving storms prevail, if the house is made tight as to roof, rear and side walls, if the open front is covered with 1/4-inch mesh galvanized wire netting, and if the house is made sufficiently deep in proportion to the expanse of open front, storms will not drive in to any troublesome extent; there will be no danger of frosted combs under all ordinary conditions, and at all times less danger than in a closed house; and curtains in the front of the house or in front of the roosts are both unnecessary and undesirable. (Woods, 1912, p. 12)
Open-air coops are designed to be deep which allows a large area of still, dry air that is warmer than outside temperatures. Because the windows are closed for winter but the screened front of the coop remains open, moist air escapes and is replaced by dry air, but there is no discernible air current in the back of the coop where the chickens roost.
Woods recommends plenty of head room above the roosts. The open side of the coop should face south and gather as much winter sun as possible. An overhang and a ¼-inch wire mesh over the windows will keep put the weather. The coop is ideally located on a gentle southern slope with sandy loam and plenty of grass. Positioning the coop with a windbreak of evergreens on the north and west and where the winds will hit the walls on an angle and not straight on will reduce drafts. Also, the water should drain away from the coop, and water falling from the roof should also run away downhill.
Woods’ book contains detailed plans for several different housing designs and materials lists as well as testimonials. Some used his open air houses in Quebec, Canada, upstate New York, and Massachusetts. One testimonial explained that his winter temperatures ranged from zero to negative eighteen degrees Fahrenheit and his flock of large, single-combed chickens thrived through the winter.
The experience of hundreds of users in extremely cold, temperate and warm climates, has demonstrated beyond question that open-front housing for poultry insures constitutional vigor, better health, better egg yield, better fertility, and more hatchable eggs, more and better chicks, greater vitality and better growth in young stock, less danger from disease germs and comparative freedom from disease, therefore assuring greater profits. (Woods, 1912, p. 21)
In warm climates, even this level of housing is unnecessary. This open air “bower” with wire to provide protection from predators is all that was necessary in the Southwest.
Open air coops are also mentioned in “Egg Farming in California” by Charles Weeks (1920) and “Profitable Poultry Production” by M. G. Kains (1910) which says, “Fresh-air houses mean cheaper construction, more comfort, no ventilation to worry about, warmth in winter and coolness in summer, more eggs, better chicks and better profits. They are believed to be the best and most practical houses that farmers can use, since they save both in labor and money.”
You can see some modern versions of these coops over on the Backyard Chickens Forum. See this thread with beautiful pictures of an open air coop in Maryland, another in upstate New York, and the beginnings of a very open aviary in Texas. There is also a discussion of open air coops on this thread.
While I wish I had seen these open air coops before building my own, I did make an effort to maximize ventilation when building my 8’x8’ coop which has definitely paid off. There is a large vent, about 1.5’x7’, along the back of the coop and a window on the side, both of which are closed down in winter. The front three windows are usually propped open. When they are not, the windows do not sit flat against the wire and still allow air to rise out. The top, thin vent is always fully open. All of the windows and vents are covered in 1/4″ or 1/2″ hardware cloth and mosquito netting. In the winter, the air in the coop feels cozy, cold, still, and fresh, and my chickens have been comfortable and healthy through winter.
Resources: Fresh Air Poultry Houses thread on Backyard Chickens; Prince T. Woods’ 1912 “Open-Air Poultry Houses for All Climates: A Practical Book on Modern Common Sense Poultry Housing for Beginners and Veterans in Poultry Keeping. What to Build and How to Do It. Houses That Will Promote Heath, Vigor, and Vitality in Breeding and Laying Stock,” which is available on Internet Archive.