P,E,I, Canada, yeah you can get some pretty nasty weather this time of year. I suggest you read this article from a lady in sunny subtropical Ontario. I’ll include three articles, more bang for the buck. I think Pat is pretty good.
Pat’s Big Ol' Ventilation Page
Pat’s Cold Coop (winter design) page:
Pat’s Big Ol' Mud Page (fixing muddy runs):
The biggest danger to chickens in cold weather is frost bite, not freezing to death as long as they are in good health to start with. A huge danger to cause frost bite is lack of good ventilation. You really don’t want to lock them up tight. That puts them at risk. But you don’t want a direct cold breeze blowing on them either. Wind chill is real. The ideal is to have openings above their head when they are roosting to get the moist and stale air out so they can breathe decent air and let their down coat keep them from freezing.
I know your weather gets a lot colder than this but I’ll share a picture I took a few years back when it was 4 degrees Fahrenheit above zero, which is about (-)15 C. I left the pop door open and let then decide what to do. They went outside. If a cold wind had been hitting them they would not have stayed outside. They really don’t like cold wind hitting them but they don’t mind the cold.