It is an ongoing discussion point or battle with those officials and builders who choose “not” to vent to the building envelope exterior.
Here is an image of some ‘mold’ coming back on the roof deck with a bath exhaust vent to the soffit.
The common thing here in TN allows bathroom venting to attic. That I have seen. Once vent penetrates attic floor the duct is bent, U shape, back down to the insulation.
That’s because the insulation will suck up any moisture and hold it so it won’t drip onto the ceiling!!! Don’t you guys get it??? 
:roll: :mrgreen:
Dryer vents are one of my picky items. Have personally seen one of my inspections after the fire. Home owner did not follow my recommendation.
If in a 2 story with dryer on 1st floor or basement vent must go out horizontal. Dryer manufactures wont honor warranty if vertical run is 12’ or more (some not all). Fan isn’t capable of pushing any farther. Longer runs create lint dams in the pipe that can cause fire.
This creates a damned if you do and damned if you don’t situation.
I see it out here now and then and it is allowed.
Kiind of like this…
And there were two.
I also like the one in the basement.