I keep my coop sheltered from the winds, but have left the door open for them to decide. In reality, it's not too bad for them but that may also depend on age, and breed.
My birds only were kept in when the temps hit 20 degrees. I shoveled an area for them once the snow came, and they usually went out for a few min. throughout the day. I made sure they had perch to sun bake and keep feet of the ground. No health issues and they were happier when given the choice. We had a time of 10 degree temps. last winter for about 4-5 days there were left in and I ended up with a huge messy fight between them. That was not fun!
My birds only were kept in when the temps hit 20 degrees. I shoveled an area for them once the snow came, and they usually went out for a few min. throughout the day. I made sure they had perch to sun bake and keep feet of the ground. No health issues and they were happier when given the choice. We had a time of 10 degree temps. last winter for about 4-5 days there were left in and I ended up with a huge messy fight between them. That was not fun!