I recently went up into my attic to put away some items and noticed frost on the bottom side of some of the boards that make up my roof. It has been quite cold the last few nights (lows around zero). I also have a metal chimney, which also had frost built up around it. As the sun hit it during the course of the day it melted and dripped on the boards I have laying in the attic. The frost on the roof boards also melted as the day progressed. I have a ridge vent, gable vents and soffit vents. What else can I do to prevent this? Why is this happening? The bathroom vent is vented directly into the attic, so I DO NOT use it for this particular reason. How is the moisture getting up there?