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Getting right down to it:

  1. I have an add-on space under a second story roof deck
  2. I want to turn it into a bathroom
  3. I cannot use AAV, has to have actual venting (I'm challenging this currently)
  4. I'm looking for proposals to place venting

As I see it, the simplest answer is to tie the washer, shower, and toilet into a wet vent. From there, I have two options:

  1. run the vent up the inside of the exterior wall of the house. I'll have to tear out the interior side of the wall all the way up to the attic crawl space and go through the top plate and second story bottom plate. This will place the vent very close to the roof edge
  2. the second option is punching into an interior second story wall you can see under option 2, this will set the vent back from the roof edge, but I may need to go through multiple floor joists. See the picture of the wall below.

Any thoughts or feedback on these two proposals? Probably looking at 1.5" vent pipe from the lav, then 2" pipe from the washer all the way to the roof.

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Here's the space:

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Option 1:

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Option 2:

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Addendum 1:

Main stack location:

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  • when you say crawl space, is this an attic crawl space? Your drawing doesn't really show the assembly thicknesses for the floors/ceilings but I can see plaster/lath so I'll assume this is 2x4 rafter tails notched and sit directly on the top plate of the top floor walls such that there really is no interface between the exterior 2x4 wall and the ceiling assembly. Oct 3, 2022 at 5:07
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    Correct, attic crawl space. I believe you are correct about the rafters. I think I can punch a vent pipe up through the exterior wall and into the attic with minimal trouble. Worst case, I can go with option 2 and put it into the interior wall up to the attic.
    – Justin C
    Oct 3, 2022 at 5:25

1 Answer 1

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Why not vent it out the small roof section of the deck? The vent would be quite small.

If you are really opposed to seeing the little vent pipe on the small roof piece then you'd just have to tie in horizontally to your main stack. Where is your main stack that already penetrates the roof?

I tend try really hard to minimize the number or roof penetrations. I only have one on my 4000 sq ft roof. It took a lot more work from the plumber but this make re-roofing easier and the vent boots are often sources of leak and need to be replaced every 10 years instead of every 30.

I like option 2 better but I'd take the vent and run it inside the attic closer to the peak of the roof. The lower the vent flashing the more water is going to have a chance to get into the roof penetration. The lower the vent the more crap that accumulates on your roof has a chance to get hung up on the vent. The farther from the edge of the roof the less impact it will have to your roof aesthetic. I also don't like the idea of a roof penetration that leads into an exterior wall, if it starts to leak it will take longer to know about it. If you vent it in the attic and can go into the attic and visually inspect the pipe you'll know it isn't causing any issues.

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  • Great question, main stack is located here, so I can't feasibly get to it.
    – Justin C
    Oct 3, 2022 at 4:20
  • I've updated the main post with where the main stack is. I can't feasibly get to it in the first story, and of course getting to it in the second story is out of the question because there is no second story. I wouldn't put it out through the small section of roof if at all possible. I don't care to smell sewer on the deck if possible.
    – Justin C
    Oct 3, 2022 at 4:26
  • There would likely be a code issue with terminating the vent in the small roof at the deck, as it would be too close to a habitable space.
    – pdd
    Oct 3, 2022 at 23:30
  • only if the deck is less than 10'. inspectapedia.com/plumbing/Plumbing-Vent-Distance-Codes.php Oct 4, 2022 at 0:14

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