Remember too, that insulated walls tend to hide pests in several forms, so the lighter you on the insulation the better! I've also seen poultry go to town on the foam insulation boards! If you decide they might be a good easy idea for the coop ceiling, just be sure they're out of reach. Don't know what's so tasty about it, but the way they go at it makes it look 10x more desirable than a warm mash with a meal worm topper!
My biggest worry in Niagara would be the damp days, so keep an eye on the moisture levels. I added an exhaust fan for those gloriously wet humid ontario summeìrs, to draw some of that moist air out for super easy cheap fix but it could easily work for the winter too (just watch for dust build up if you do)! But if you really want to get an idea of how warm those little ladies can be, snuggle a hen on a cold day!