The weather here may differ from yours, but when it gets into the negatives my chickens do fine. They have insulation in their shed, and they sleep in a pile to keep warm. I give them extra food and water, and if it's going to be extra cold or there's a blizzard coming, I give them a suet cake. I don't have a water heater so I refill their bowls with warm water throughout the day.
A problem that I encounter are my leghorns, because they get frostbite on their combs. Some nights I have to take them in if it's too cold. My other hens do not have much of a problem with the cold because they are cold hardy breeds like the Rhode Island red. My black and red sex links do well in the winter too. My friends have had some of their chickens die in the winter from cold, but I have had none die during the three years that I have kept chickens.
A tip that I would definitely recommend is not to buy plastic feeders/waterers/anythings for your hens. My hens are very clumsy and they broke all of their plastic things, lol.