While not getting all fancy with building wrap, vapour barriers etc works for some, those of us in cold climates up north need to realize that many months of sub zero temps can provide breeding grounds for mould if not detailed properly.
Up here in canada, we have a motto. Seal tight and vent right. Which means continuous vapour barrier on the inner third of the insulation (or better yet, on the inner face), and yes, mechanical ventilation. I live in a war time story and a half, and the first year I lived in it, I replaced all windows and sealed up all outlets, switches etc. as well as replacing the old chimney furnace with a high efficiency furnace, thus eliminating the air exchange in the house.The second winter we all fell sick as I had made my house simlar to placing your head in a plastic bag. Third winter , I had installed an HRV, and we all breathed better. The HRV was 1500 bucks installed, but now with our sealed tight vented right house, the natural gas bills are around 400 bucks a heating season.
Those who want to tell me I'm wrong, hey,, how cold is your winter? It is an issue.
hope this helps. Cold climate building is another thing.