Oregon - Page 925
We put up plastic at the vent holes in the coop. Each hen produces 10 watts of heat that helps them out, not sure if that is all breeds or not, I would hope it would be. At the bottom of the door was a gap so we just stuck a blanket down to block out the cold/wind.
Up at the top of the coop the air vents where left open. So far this has helped, this will be their third fall/winter for seven of the ten.