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I'm helping a friend install a sink in a workshop that was added onto his house. A previous owner installed a water line and a drain by boring through what appears to be the rim joist of the original house into the workshop but they did not vent it. I am reusing the holes they bored and want to vent the drain properly. My original plan was to install an AAV in the wall above the drain but after removing some of the stucco, it appears there is a stud directly above the drain pipe. The stud cavity to the right does not have enough room to fit the AAV box I picked out. I opened the stud cavity to the left and found that the drain goes through the end of the rim joist and has a sizeable amount of sill plate and framing above it. I am worried about notching/drilling through this part of the framing to accommodate a vent pipe.

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What should I do? As far as I can tell, my options are:

  1. Notch/drill through the sill plate and remaining part of the rim joist to install the vent pipe/AAV + box in the left stud cavity.
  2. Install the AAV in front of the wall. Is this even legal?
  3. Install the AAV in the crawlspace behind the wall. This would almost certainly be at a height below the P-trap its venting and several feet away. Would this still be effective?

Do I have any other options?

  • Is the trap under this sink currently being sucked dry by other drainage? What is happening that causes you to want to install a vent? Could you just install an air admittance valve beside the sink? – Jim Stewart Nov 25 '17 at 16:22
  • There is no sink there currently. We plan to install a utility sink so it’s ok if it’s a little ugly. I’m just looking for effective and legal so installing it in front of the wall might be an option – Thaumaturgic Nov 25 '17 at 18:10
  • I would assume that code specifies that an AAV must not be closed up inside a wall. – Jim Stewart Nov 25 '17 at 19:18
  • If you would install a vent that goes up into the attic I presume you would connect it to an existing vent pipe since taking it through the roof would involve installing another penetration in an existing roof. Still this is a lot of work compared to an AAV. Is the horizontal black drain pipe in the picture what you are installing or was it previously installed? – Jim Stewart Nov 25 '17 at 19:30
  • Correct, I wouldnt seal the AAV in the wall, the idea was to put it in a box like this at an appropriate height: homedepot.com/p/… The pipe sticking out of the wall is illustrating the hole that was previously installed. I think my plan is to try and drill through the sill plate and try to get a short 22 1/2" bend to offset the pipe to the left cavity – Thaumaturgic Nov 26 '17 at 0:02
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Option 1 is fine. There's nothing load-bearing about the rim and plate at that location. I'd bring the wye up at 22-1/2 from plumb to move away from the stud.

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An AAV can be installed as long as it is 4" above the trap. Just add a vertical to that run and put the AAV above the line.

That would be your easiest solution anyway.

Otherwise, as Isherwood points out you could add a vent to the run but that looks like a lot of work for what it's worth.

Good luck!

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