Mine are outside and if you look at my BYC page you will see that i use a tarp for part of the wall covering. It is 5 degrees with -18 windchill. I did put 2 heat lamps and made a cookie tine heater for the water plus I put some yard furniture cushions around the chicken wire portion of the coop. they seem to be doing fine and even started laying. I also put some cayeene in the water and gave them a bit of whole and cracked corn and some Black oil sunflower and scratch to build up body temp.