I have noticed condensation on a few ceilings in our house. In the bathroom it is at all times, not just when someone is using the shower. It is butting up against an outside wall. I have also noticed wet ceilings in two bedrooms, again, butting up against an outside wall. I don't believe our roof is leaking as it is only 4 years old. We live in Wisconsin where the weather is currently below zero. Would this be an attic problem? We blew in insulation a few years ago. We run the bathroom fan when we shower. What do we need to look for?