You have to understand before I even begin that I am being facetious when I say thank goodness for duct tape.
From outside this house we saw a rather large vent covering on the front of the house. It was rather ugly too, and damaged as if it had been hit by a fallen tree limb.
Of course my client asked me what it was. "A vent cap. Likely a bathroom vent, but we will see once we get into the attic."
Little did we know what we would run into in the attic!
It was an older house, and both bathrooms had new vents. And they both had new, wonderfully plastic vent tubes which met inside the one wide vent directing their air toward the attic penetration.
The smaller bathroom vent tubes each barely entered the wide tube. So how much air was actually exhausting outdoors is minimal.
But the wide tube is not even directing the air toward the hole!
Fortunately, though, the tube is held in place (not the right place mind you, but in place) with DUCT TAPE!
And not that fancy, schmancy aluminum tape.
Actual DUCT TAPE!
It is not going anywhere!
Well, actually, I'm not sure about that.
But I am sure that this is not a very effective vent.
The reason there is no mold on the sheathing is probably because not much air is actually getting to the roof!
In order to accommodate both bathroom vent tubes, he bottom of this wide tube is positioned such that for the rafter, and DUCT TAPE, to hold it in place, it cannot really be directing the air outside the house. So it is a failure in every respect. But to fix it into this incorrect position intentionally, and with DUCT TAPE, might not be the mark of a true professional. Who knows how long these sellers have lived with this installation.
My recommendation: be sure to check the attic space! You never know what you might find! When people ask me what in the world I could possibly be interested in when I go into the attic I say that there are more than a dozen things I want to look at, and only one of them is the underside of the roof!