you don't have to use fiberglass insulation, they make curogated plastic insulation that is as thick as a curogated cardboard boxes. One layer right on top of the coop, 6 inches above that make another layer possibly with a roofing material over top of that. ?Thank you!! We had talked about that when building the coop... But didn't do it... I should have raised the roof so air could go underneath..... I'm pretty sure I can isolate it to where they won't eat it.....