We would call this phenomenon "winter". Or, at least, November. :D
My chickens would be digging their sweaters out of storage.
Sounds like a ventilation problem. Or roof leaks. Top-hinged nest boxes are notorious for leaking at the hinge.
I chose mainly heat-tolerant breeds.
I give them constant access to fresh water, weekly electrolytes (along with, not instead of plain water), access to dirt where they can dig down to a cooler layer, as much shade as I can provide, and have lots and lots of ventilation in the coops:
The...