DWV Vent Near Bathroom Skylight

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Doug Henningsen

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If I understand the code (UPC in CA), my choices are:
  1. Run vent line >3' above the height of the (opened?) skylight. If I do this, from what I've read, it's advisable to paint ABS pipe to protect it from UV rays - correct? A 3' pipe would seem to need a brace but properly secured below the roof, it should be secure - correct? Is there any code on these items?
  2. Run the vent line >10' away from the skylight. The DWV is for a single bath with 8' ceilings in a house with a flat roof. Can I run the 2" vent line 10' horizontally before it goes through the roof as long as the pipe is slightly sloped toward the drain?
Related to the bathroom DWV - if #2 is not permitted for some reason, is it possible to run the DWV 20"+/- horizontally before going through the roof to properly align it with an existing roof penetration?

Thanks!
 
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wwhitney

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Agreed that those are your two choices per https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/9/vents#906.2

1) Yes, paint the ABS, or my preference, use a different material above the roof, e.g. 3" copper DWV, transitioning just below the roof deck. Although 4' of 3" copper DWV might be pricey.

Not sure on bracing/securing.

2) Sure. If running through solid sawn joists/rafters, they would need to be a minimum depth of 7.5" to accommodate the 2-1/2" hole required for a 2-3/8" OD pipe. That would exclude modern 2x8s (7.25" in depth).

Cheers, Wayne
 

Doug Henningsen

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Agreed that those are your two choices per https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/9/vents#906.2

1) Yes, paint the ABS, or my preference, use a different material above the roof, e.g. 3" copper DWV, transitioning just below the roof deck. Although 4' of 3" copper DWV might be pricey.

Not sure on bracing/securing.

2) Sure. If running through solid sawn joists/rafters, they would need to be a minimum depth of 7.5" to accommodate the 2-1/2" hole required for a 2-3/8" OD pipe. That would exclude modern 2x8s (7.25" in depth).

Cheers, Wayne


Thanks Wayne. Regarding the joists (#2) - and I should have addressed that in my question. I lucked out...the joists run from front to back of the house, so I'll run the vent between the joists. And I think #2 is preferable - more distance between a vent and skylight is better. Under option #1, on a warm calm day with skylight open, I fear parfums de sewer slowly spilling out of the vent and directly into the skylight.

Just curious - for educational purposes - is there a limit to how far I could run the vent horizontally as long as there's an appropriate slope?

Thanks again!
Doug
 

wwhitney

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Jadnashua

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You don't want rain, snow melt, or condensation to block your vent line, or accumulate, so appropriate slope is a good idea. In an unheated attic, any accumulation could also freeze, but that's unlikely where you live. In places where freeze is a normal occurrence, using a larger pipe through the roof is often called for to prevent hoar frost from closing it off.
 

Doug Henningsen

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If I'm reading Table 703.2 correctly (I just glanced at it), a required 2" vent can be 120 feet long, of which 40 feet can be horizontal.

https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/7/sanitary-drainage#703.2

As to vent grade, apparently level is allowed, but 1/4" per foot back towards the drain is better.

https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/9/vents#905.1

Cheers, Wayne

Huge thanks Wayne and Jim for your insight. Wayne, thanks for the references to the code.... I need to get friendly with Mr. Code, and that helps.
Doug
 
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