My coop is old and the salvaged lumber doesn't really make a snug draft free fit so since 1989 I've been saving old feed bags and paper grocery bags to line the inside doors and walls. It works well at keeping the drafts out and gives the inside of the barn a kind of homey, nostalgic feel. I cover the windows in heavy duty plastic too. 4 mil to 6 mil when I can get it. Back door to the barn is made from slavaged kitchen cupboard doors and lined in feed bags and grocery store bags. the front entrance is Dutch doors also lined in old bags. I scribble notes about my birds on the lining with a crayon some years. This door gets so much use, I often change the lining when it tears. I don't need to heat this barn. Ever. The deep litter puts out a little heat and the chickens like to nestle into it after eating. I've never had water freeze in the buckets inside the barn in over ten years. Our winters are not as cold as they used to be.