How cold can they stand?

OH, I remember I was so worried for my hens when they had their first winter. If your chickens have small combs, that's a good thing because the combs can freeze. The main thing is keeping them out of the wind and keeping them from getting wet. Also, if they can roost on a 2x4 board (broad side up), then they can sit on their feet to keep them warm. I'm in Ohio, and we get some extremely cold temps, like you do.

If you can keep a heat lamp in your coop, thats great because those really help.....and it can help keep their water from freezing too. And if you use the deep litter method, you can go through the winter without cleaning out the coop entirely....but good ventilation is important.

Using the garage is up to you......if you've got a good coop, maybe you can just use a heavy duty outdoor extension cord to put a heat lamp in it.....

 

The standards can take a lot of cold as long as they aren't in a draft. I agree with chicmom about the roosting board set up. If they can keep their feet flat, they can keep them warmer. The chickens will produce a lot of moisture so even in the winter, you have to think about ventilation. More than you think you will need. Moist air can lead to frostbite so inspect your chicken's feet, combs, etc. often during winter.

 

We are on our fourth South Dakota winter with chickens. As the other have said, keep various perches available for them to roost and hang out on. They will sit where they are most comfortable. Drafts need to be eliminated and at the same time have steady ventilation. I use natural ventilation...an opening down low at floor level that is louvered and also two up high, also louvered. These have screens to keep the bad guys out.

Chickens are tough animals. The cold weather breeds we keep sometimes get their combs and waddles nipped by frostbite. In the spring they always heal up with no ill effects.
The last two winters have seen our coop inside temps at around 20 below zero. We turn on the heat lamps for their comfort on the nights below zero. Even with them on they usually choose just to stay fluffed up and away from the lamps. As long as no wind is going through your coop they will be comfy.