It's supposed to hit 19 or 20 below zero tomorrow. (29 below Celsius). My Coumbian Wyandottes are very cold hardy, and they play outside when it is 5 below, but this is getting downright severe. It hasn't been that cold here for 40 years, so I figure the past 30 or so generations of their evolution has not been exposed to such cold weather. Also, my flock is small, just 5 of them, so they don't generate the shared body heat of a larger flock.
In additon, I can't keep their water from freezing when it gets below about 10 degrees below.
Others on BYC would advise I ignore it and let them deal with the cold, but I spent a few hours today building a contained run with perches, food and water down in the basement. Moved them down there this afternoon. They were pretty agitated at first (strange new environment is never easy for chooks), but eventually they settled in on the perch and went to sleep.