It's not about giving them a warm place to sleep, it's about allowing them to keep themselves warm. To keep themselves they need two things, a way to get out of strong winds and they need good ventilation to avoid moisture build-up which can lead to frostbite. I don't know what your run looks like or how much wind protection it provides but it almost certainly provides great ventilation.
When I was a kid we had one stretch where the temperatures never got above zero Fahrenheit for several days and nights. I can't remember if it was 5 or 7 straight, it's rough getting old. We had a few chickens that slept in trees and were OK. Those trees were in a sheltered valley so the wind wasn't as strong as it could and they had the freedom to roost wherever they wanted to in those trees. They could hide behind the trunk. The way their feathers lay if they face into a breeze they can handle a lot more wind than if they are facing away from it. They tuck their head under a wing. Just like the wild birds that overwinter they can handle cold if given just a little help.
Sometimes when we build coops or runs we take away their ability to find good spots. We may create wind tunnels they can't get out of. If you consider your run predator proof then predators are not an issue. I prefer mine to sleep in the coop mainly because my run is not totally predator proof. My coop has great ventilation up high so moisture does not build up. Your cold by itself is not the issue. If your run offers reasonable wind protection they might be fine out there. If your coop does not have good ventilation they may be better off out there. I don't know which is best from here.
I took this photo when it was 4 degrees above zero F. I left the pop door open and let them decide what to do. As the wind was not blowing they chose to enjoy going outside. They can handle cold better than many people think.
When I was a kid we had one stretch where the temperatures never got above zero Fahrenheit for several days and nights. I can't remember if it was 5 or 7 straight, it's rough getting old. We had a few chickens that slept in trees and were OK. Those trees were in a sheltered valley so the wind wasn't as strong as it could and they had the freedom to roost wherever they wanted to in those trees. They could hide behind the trunk. The way their feathers lay if they face into a breeze they can handle a lot more wind than if they are facing away from it. They tuck their head under a wing. Just like the wild birds that overwinter they can handle cold if given just a little help.
Sometimes when we build coops or runs we take away their ability to find good spots. We may create wind tunnels they can't get out of. If you consider your run predator proof then predators are not an issue. I prefer mine to sleep in the coop mainly because my run is not totally predator proof. My coop has great ventilation up high so moisture does not build up. Your cold by itself is not the issue. If your run offers reasonable wind protection they might be fine out there. If your coop does not have good ventilation they may be better off out there. I don't know which is best from here.
I took this photo when it was 4 degrees above zero F. I left the pop door open and let them decide what to do. As the wind was not blowing they chose to enjoy going outside. They can handle cold better than many people think.
