"is it ok to run vent pipe in exterior walls? "

Yes. Does that mean you can, in your situation? If money is no object, yes.

You need to verify whether the change conforms with good practice, and AHJ.

If you're in a freezing climate, you need to insulate. Not for the vent's sake.

i am planning on replacing vanity which butts up against wall. this is the time to address the vent pipe. i am not moving vent cuz i am bored. i will need to patch sheetrock for wall and ceiling so it is a bit of effort. 1st floor bath is 1/2. sink/toilet. 2nd floor bath is 3/4. so all 5 devices use vent. perhaps vent is bigger than 2"? outside wall is 2x4. so maybe thats why vent is inside this stub wall.

Hey Joe mn,
I have the exact same situation where i need to vent my sinks through the outside wall. I moved my sink from one wall where it's already vented to an adjacent wall (exterior). I replaced the single sink with a double sink vanity. My question is do you run the vent inside the wall and through the roof (STRAIGHT)?
The only possible problem I see with this is that it may be hard to flash the vent since it's too close to the edge of the roof. If this is commonly done, I'll probably do the same.
If it's not common, then I was thinking of running it through the wall up to the ceiling/horizontal studs, then do a 90degree and come horizontally a few feet back towards the center of the house (where I have more room to work), then vent it through the roof.

anyone has ideas?
thanks,
Max

You may run the vent in the outside wall and the eaves should extend out far enough to permit flashing the vent without problems,BUT;

Before you move the vent there are a number of code issues that must be considered.

It is assumed that the vent met code at the time of original installation however if you change the original configuration in any manner that constitutes "New Work" and the entire vent must then conform to the code that is in effect at the time of the change.

It then depends upon which code you are under;

Under the UPC if the horizontal offset is equal to or greater than 3' the entire length of the vent must be increase by one nominal trade size.

Under the IRC if the TDL (total developed length) of the vent line exceeds 40' you must increase the entire vent by one nominal trade size.

In regions subject to frost the vent line MUST BE increased to 3" at least 1' inside the structure. (some local codes require 4"). This could be problamatic when running up the outside wall and through the roof.

Under both codes unvented fixture arms may not be connected to a vertical stack below the point where a watercloset is attached. This means that if your current stack is serving bathrooms on both the 1st & 2nd floors you would be required to install sparate venting for the first floor or a separate waste stack for the second floor.