My bad, I probably worded that completely wrong. I've always equated dry to be low humidity, I should have expounded on that a bit better when I stated "dry is key". Apologies for the confusion.
I'm a bit new to chicken keeping as I've only had my ladies for about a year, so I am no expert.
I have always been under the impression that having ventilation in your coop is a must, as it ensures that harmful ammonia from their droppings is able to escape. Chickens are little space heaters...