Thought I would add my $.02 here. I used to get all worried about the cold until I visited a flock in Western MA. Their "coop" was hardware cloth inside a barn. 3 sides were the walls of the (uninsulated) barn and the other side was completely open wire, and the barn was as cold as the outside. They had no heating lamps, no warm food, no blankets or Mozart. I realized then that I was being a helicopter parent and I could relax. Just give them an area that protects them from the wind, but doesn't build up moisture. And make sure their water doesn't freeze.
So sorry to hear about Diane's frostbitten chickens!
This is what I wrote in a different thread:
Every year we "winterize" the coop. I have an Eglu which opens onto a larger 10x10' run. We wrap the Eglu portion of the run in a plastic tarp to create a kind of hoop house. We cut vents in it so moisture doesn't build up and chill them. I also have a waterer that has a heating element in it so the water doesn't freeze. The chickens have access to the larger, open run if they want, or they can hunker down in the hoop house portion to stay warmer. The roosting part of the Eglu is insulated, so they keep warm through body heat. It's been about 6-7 years of keeping chickens this way and everyone seems fine.