What temps do you guys feel are ok for chickens without a heat source? I'm from up north, but now live in GA and I never really consider it too cold here. My pups don't even come in because they think it's more comfortable outside on the patio than in the house! But my coop is going to be very 'open' so do you guys think I need to board it up a little when it gets a little chilly here (maybe just under freezing)? thanks.