Just as humans need fresh air, chickens also require an abundance of breathing space in order to be comfortable and healthy. However, in contrast to humans, you will also have to take care of the dropping that your birds excrete.
Chicken droppings have a high content of ammonia, and this is as toxic to them as it is for us. Also, chickens prefer open spaces to closed, stuffy ones and need their coop to be adequately ventilated.
The most common and easiest way to ensure this is to add windows or vents in the walls of the coop. you can also consider constructing the entire coop out of wire mesh, but this is not a viable option except for when you live in a temperate climate where the risk of predators is low.
Using wire mesh will certainly not shield the chickens from extreme weather conditions and they will not be able to feel safe from predators.
Remember, the only purpose is not to just let fresh air enter the coop, but air needs to go out as well to ensure proper ventilation in the coop. For this, you can incorporate the natural movement of the airflow as a part of the design, and consequently avoid paying for costly mechanical airflow systems.
Warm air rises, therefore it is best to place the vents at the top of the walls of your coop. Add a door placed low on the wall facing the direction where the winds usually blow from, and you will considerably improve the ventilation inside the coop.
Even though chickens generally prefer cool temperatures, they never appreciate the cold. If the weather in your area gets very chilly during winter months, you should add sliding windows to your design, so that you can control how much they open.
This way you can have the windows open just a crack during the winters so that you don’t block out ventilation completely. If your hens are feeling too cold, they will not lay so many eggs, so it is best to keep the temperature monitored inside the coop.
Ventilation is important during the summer months as well because it will allow your chickens to remain cool. It will also keep the moisture levels low, and your chickens will be less likely to fall ill. It is not a bad idea to invest in a mechanical ventilation system, but this is not needed for smaller setups.