Here in Texas we are having what is locally known as cold weather at 27F degrees. (I'm not from around here).
I had to take special precautions for my chickens. They already let me know they do not approve of exposed roosts during cool weather. I corrected that once I realized the entire flock had spent the night crammed into one nest box.
The coop is a masterpiece of opportunistic construction from salvaged materials. It is half plywood and half farm fence. This is great for the Texas summer, but it is as useless as something colorful on a bull when it is cold enough to freeze something colorful off a brass monkey.
To protect the birds from drafts I put 6 mil plastic sheets up with roofing nails. That, and a bit of clear duct tape, sealed things up on two sides. The narrow end with the pop door has no coverage. The long side with the people door has a three foot stretch of uncovered wire as well. All told, the coop has 35 square feet of ventilation. The rest is covered. Especially around the roost.
There is no insulation. The litter is not very deep. There is no water heater. There is no heat source.
The chickens are heated internally! They have a warm blooded metabolism. They have feathers. They have a roost that lets them keep their feet flat and settle their fluffy feathery bodies on them. And they get a double ration of insanely delicious Black Oil Sunflower Seeds at night.
Now there may be an issue with ice in the waterer by morning, but they really do not drink much water while they sleep. The big risk is that the moisture they emit while sleeping (and pooing) will build up in the coop and in their little chicken lungs.
So there is the strategy. Keep the chickens out of the wind. Keep them dry. Give them a little extra food.
Meanwhile, I am wearing a down jacket.
I lost a chicken to the cold because I failed to follow my plan. I failed to cover part of the coop where a horizontal rain could soak the birds and bedding, foiling my "keep them dry" concept. I have since put more effort into making sure the coop is dry and non-drafty. The chickens have been fine through multiple colder rainier weather events with no problems.
BackYardChickens.com member patandchickens has an excellent winter coop discussion posted there.