Make sure that all exhaust vents are vented to the outside of your house, not into the attic space. Although your attic space may be a cold zone, isolated from the warm interior of your house, it cannot efficiently rid itself of moisture without the assistance of exhaust vents.
Steamy showers can be a relaxing way to unwind, however, without an exhaust fan to eliminate the hot air, mold can begin to accumulate. If the bathroom is vented into the attic space itself, the moisture will buildup and decrease the life of your shingles as well as rot the roof deck and trusses.
How to Prevent Condensation in Your Attic
Not only do you need the roof itself ventilated, all exhaust hoses need to lead outside. All vents need to be separate from one another, this means you cannot bring more than one vent into a common vent stack because one may overpower the other and feed the moist air back through the weaker intake.