When keeping waterfowl indoors, a thick layer of bedding in pens and shelters reduces the penetration of cold from the ground. The deep litter also produces heat through decomposition of the litter and manure. Now for chickens - mature chickens can usually adapt to extreme weather if the exposure is gradual. Breed plays a role in weather tolerance. But cold weather adversely affects lightly feathered breeds and breeds with short close feathers.
Crested varieties are vulnerable to freezing if their crests get wet.
Single combed breeds are more susceptible to frostbite. Cocks are more susceptible to frostbite than females because they don't sleep with their head tucked under their wing. A well ventilated coop is a must year round and the more time your chickens spend indoors the more important ventilation becomes. Ventilation supplies fresh air, removes dust particles and harmful gases from the air, removes moisture, and dilutes disease causing organisms that build up in a closed house. Ventilation holes near the ceiling along the south and north walls promote adequate ventilation.