Our coop has 1/2 inch insulation board between the walls. It's quite comfortable in there even on hot days. It also has two windows (covered with hardware cloth). One window faces north and is approx. 7 ft. long. The other window faces south and is approx. 4 1/2 ft. long. There's also a window over the door (south side) that we'll need to cover with a board if it gets really cold. I have 18 LF brahma, 6 months old today. I'm trying to decide at what nighttime temp. I should start putting down the shutters that cover the windows. So far they've done fine with all that air circulation. Thanks.