This is a view of the inside of my girls' coop. They have been in it since October, and last winter was brutal. I really need to insulate the single steel panel sides. As you can see there are 2x4 supporting structures that as of now I'm using to support the roosts and a (not shown) feeding table. There are 3 windows plus a roof ridge vent the length of the coop, and it really vents well. I don't want to interfere with the ventilation, but I have to do something about the cold walls. My tentative plan is to use 1" blue styrofoam insulation between the studs and then cover the walls between the studs with something. I looked at 3/8" plywood (and 1/4" plywood) yesterday, and as we were wandering around Lowes, my husband spotted the wall paneling that is used to panel below chair rails -- little grooves every 2 or 3 inches that run vertically. It has a vinyl finish that might be more resistant to poop stains. I'm still leaning toward the plywood (painted with glossy outdoor paint of course), but my DH is lobbying for the lighter weight stuff. It appears to be only 1/8" thick or so and looks like it is some sort of pressed board under the coating. My plan is not to insulate the ceiling completely since a good deal of the ventilation is up there. Too much sometimes, I had some snow in the coop that had come in through the ceiling vent, but that was only once and during a blizzard. There are gaps between the metal siding and the framing lumber at floor level, and I've worried about rodents getting in, so that is also where some of the ventilation was coming from, I'm just not sure how to handle that either. I toyed with the idea of stuffing the holes with crumbled up chicken wire so that it wouldn't interfere with the air flow and would keep the undesirables out, but my insulation will mess with the ventilation anyway so maybe a more permanent filler is in order. I'm going to get a Sweeter Heater for overhead so I don't have to use the red heat lamp (made me nervous all winter) hooked into a thermocube. I just want the girls to be more comfortable, and -10 isn't comfortable by any standards. Does anyone have any better ideas? I have to do something better for the girls this winter.