Ah mold. It is such a hot button. I know just by putting the word MOLD into my title this post will get attention.
People are interested, but I am still surprised at the lack of knowledge or the inaccuracy of knowledge (even you agents who need to know the basics).
This is not intended to be a general knowledge post. (go here for that) This is a heads up for everyone on the issues concerning acurrently accepted means of exhausting bathroom vents. It is acceptable, by International building codes to duct bathroom vents to an attic vent (any vent). This is usually a good thing and definitely better than venting directly into the attic. Recently I came across a very new home (only four years old) that had some mold growth in the attic. Not really a huge amount, however mold spores are microscopic and you cannot determine if it is affecting Indoor Air Quality without getting a lab involved. With closer investigation it could be noted the exhaust fan for the shower and toilet area was ducted to the nearby soffit vent. This is currently acceptable by building standanrds however in this case it was the root of the issue.
The way an attic vent system works is like a chimney, as the roof heats cool air is pulled into the soffit vents and hot air is exhausted out the ridge vents. So as the diligent home owners ran their exhaust fans during the steamy shower all of the warm steam was pointed at an intake vent!! All the moisture exhausted toward the vent and promptly turned around and was able to condense on the cool attic surfaces as the soffit vent did its job.