Much like humans and all other animals, chicken coop chickens need to have plenty of breathing room to stay in optimal health. The problem is compounded for chickens because, unlike most humans, you also have to worry about the droppings which your birds excrete.
These droppings are high in ammonia, which is just as toxic to poultry as it is to us. Chickens also do not like stiflingly enclosed spaces or the heat which can accrue within them.
For these reasons and more, it is important to ensure that any chicken coop you design and build has plenty of room for adequate ventilation. The most common ways to account for this need are to include some kind of window in your chicken coop design.
There are also methods which involve using a wire mesh instead of solid walls for the entire coop, but these are generally not a good idea unless you live in a very temperate climate with few predators. Wire mesh will not protect your birds from drafts and rain, which they do not care for, and will also not give them a “safe” feeling place to hide from any predators.
In addition to just getting fresh air in from the outside, you want to make sure that there is good air-flow within the coop itself. You can use the natural way that airflow moves to your own advantage when doing this part of your design, and avoid having to pay for expensive mechanical airflow systems.
Remember that warm air rises, so that by putting a window towards the top of your coop, you will allow it to escape and keep the air near the bottom more fresh. A low-lying door or window on the side of your coop which the winds usually blow from will help the process considerably by providing more cool and fresh air to push the stale, warmer air up through the higher window.
While it is true that chickens generally prefer cooler temperatures, they do not like it to be too cold. If you live in a climate where the weather gets cold during the winter months, you may wish to consider installing windows that allow you to change how much they are open.
This will enable you to leave the windows open only a small crack during the cold season, just enough to let out the stale air without making your birds too cold. Hens who are too cold will not lay nearly as many eggs, so it’s generally a good idea to monitor the temperature when you ventilate your coop.
You can get electronic systems which will monitor it for you, or you can just keep a close eye on it yourself.
During the warmer seasons of the year, ventilation is important because it will keep your chickens cool. It also, throughout the year, keeps moisture levels down, which helps to decrease the risk of disease from ammonia or carbon monoxide, the unchecked build-up of which can even lead to death in extreme cases.
If you have money to spend, it is possible to purchase a mechanical ventilation system for your chicken coop, but for smaller setups, this is usually not necessary. Large poultry farms which have hundreds of chickens in one gigantic barn structure often use these systems, which differ surprisingly little from the air conditioning units used in people’s homes.