We can get down to -15° here too, so I understand your concern. We found out after we purchased this farm that we are in the coldest, windiest spot in Ohio.
Our hen house is a portion of our old (1880's) barn. We used rubber horse stall mats over dirt for flooring, which we cover with wood chips and straw for bedding. During summer, we only have about an inch or two of bedding on the floor.
We use deep litter in the hen house all winter long, adding an inch or two of straw and wood chips every week beginning in autumn. Turn it once a week and it will help heat the area for the birds.
Like I said, we save the corn for winter feeding. For the past two years, we dried 12 1/2 dozen and 15 dozen ears of sweet corn for them. We still ending up supplementing with cracked corn from the feed mill. This year our corn got flooded out, so we have been purchasing corn.
We only insulated the walls with the biggest drafts and the ones by their roosts. Even putting sheet plastic up to block some of the wind helps, if you don't want to or can't afford to insulate the entire barn.
We put alfafa, clover and timothy hay bales in there for the flock when there is no green showing in the farmyard or pasture. I also have hanging wire baskets that we fill with fresh veggies for them. They have to jump to reach the veggies so it gives them some exercise and helps keep them from getting bored when they are stuck in the barn for days at a time.
Occasionally, I've used a small space heater in the barn, but that was more for my comfort than their's.
If you have cold hardy breeds, they should do fine. You could also put some straw bales in the barn along the walls to help block the wind. We found piling snow up on the north side of the barn also helped.
We have a water pump in the barn and have it wrapped with heat tape, so we have water all winter long. However, we have had to change the water out as much as four times a day when the weather is at its worst. We tried a heated dog bowl for water, but the flock seemed too interested in sitting on the cord, so we removed it. So we use heat lamps in winter. We usually put the waterers in the area of the heat lamps.
We keep feed out 24/7 for our flock, along with fresh water year round. We keep all the feed in the barn and hen house. I fill up the feeders in the morning and check them at night. Our ladies have found out that if they twirl the feeder often enough, the wingnut underneath flies off and all the feed falls to the floor.
We've changed out the nut four times, and are hoping that this new one will hold. If they dump the feed, I don't fill the feeder until the feed has been eaten.
Purina has a (non-organic) Flock Block, which is kind of like a wild bird seed block, which our flock loves in the winter. It is 8% protein, with corn, wheat, milo, barley, sunflower seeds, oyster shell, grit, vitamins and minerals in it. It is also made with molasses. Between that and the hay, the barn smells great. (At least I think so)
My folks raised chickens too. Ours are definitely spoiled pets in comparison!
edited: now if I could just type!
