When I inspected this townhouse it was 12 years old. For twelve years the ducts from the two upper bathrooms have been venting into the attic. These vents had never been terminated to the exterior at caps with back-draft dampers. This installation can result in considerable moisture being vented into attic space. The staining at the ends of these ducts are evidence of such moisture.
Under the right conditions, this moisture can condense on the roof sheathing and lead to mold/fungal growth—-as can be seen in this next picture—-in a different house.
All exhaust fans should be terminated to the exterior of the home, at a proper vent cap with a back draft damper. The ducts are required to be insulated by current regulations as well—just like the ones in the first picture that are improperly terminated. These two vents could go to termination points at either the side wall or through the roof. On homes like this, that are 3 stories tall with very steep roofs, it is preferable (for maintenance purposes) to terminate at the side wall.
Charles Buell, Seattle Home Inspector
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