Relocating a plumbing vent in the attic

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Old 12-29-13, 03:06 PM
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Relocating a plumbing vent in the attic

Hello,

I'm about to re-route a plumbing vent on the front of my house for solar panels I'm installing (The things I do for my own house, that I would never bother with for my customers!). I plan on cutting it below the roof sheathing, putting a 45 on it, and bringing it up the roof and just beyond the ridge to install the flashing collar on the back roof. I have a few questions:

1 - Is there a special PVC glue that is used for plumbing, or can I use any PVC cement? Do I have to use the purple primer first?

2 - The vent has an outer circumference of ~11". I'm guessing this corresponds to a 3" PVC pipe? I just realized today that there is a 2" PVC pipe coming from somewhere else in the attic that tee's into it right where I need to cut it. I figured I'd cut it below that tee, and then I'll also end up rerouting the 2" pipe to tee into the new 3" section I'm going to add going up the roof. One thing I noticed, though, is that this 2" pipe has almost no grade to it, it tees into the existing 3" pipe almost perpendicular. My new route is going to give it a lot of slope. Is it possible that this smaller pipe serves a different purpose, and I may not want to change the grade.

3 - I was at Home Depot today looking for a 3" tee with a 2" outlet to fit this application, and couldn't find anything. Is there a better place to source this kind of stuff?

Thanks. I appreciate your time, and feedback on anything else I need to be mindful of would be most welcome.

Elie
 
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Old 12-29-13, 06:48 PM
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Your plan sounds reasonable. You generally want a 1/4" slope (1/4" rise for every 1' run). Though a steeper slope should be fine for a vent pipe (you wouldn't want it for a drain though).

You'll want to use PVC cement. While any kind may work, I wouldn't want to risk a leak using some odd-ball PVC glue. I'd spend the few dollars and get PVC plumbing glue and primer and do it right.

As for the primer, all plumbing codes require primer (usually purple primer specifically) on drain pipes. Everywhere I've done plumbing work, the inspectors have required it on vent piping as well, though I understand some locales allow vent pipes to be assembled without primer. A call to your local building office could probably get you an answer - or just use the purple primer first.

You should be able to get a 3x3x2 sanitary tee anywhere, they are very common. If you can't find one, a 3x3x3 sanitary tee with a 3x2 reducer could work too. Make sure the sweep of the tee is facing downwards... The way I remember is to picture rain coming in from the roof vent, you'd want it to slide down the tee gracefully and not have to go back 'uphill' to the tee.

One other suggestion, you may want to have your new vent come up out of the roof a few feet down the roof. If it's right near the top, you may see it from the front of the house and it may look funny. Dropping it a few feet down the roof it'll be hidden by the peak of the house.

-Mike
 
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Old 12-29-13, 07:05 PM
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Make sure the sweep of the tee is facing downwards...
Upwards on a vent san tee....
 
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Old 12-30-13, 03:51 AM
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Awesome, thanks for the help Mike. What would you guess that 2" pipe is? It runs flat for about 10', then takes a 90 turn to the right for about 10' (still flat), then tees into the 3" pipe. I can't figure out why there's no slope to it. I had heard the rule of thumb you mentioned about 1/4" rise for the vent pipe. Is it possible that this 2" pipe is a drain, and I want to keep the slope flat, or at least very low?
 
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Old 12-30-13, 06:48 AM
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That pipe is a vent.. It should have upward slope towards the 3" pipe........
 
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Old 12-31-13, 06:54 AM
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Upwards on a vent san tee....
Thanks Mike - it made sense in my head, maybe not so much after I typed it.

The sanitary tee used on a vent should be in this orientation:


-Mike
 
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Old 01-05-14, 12:20 PM
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I finally got my tyvek suit on to crawl up to this thing, and inserting the new elbow to reroute is going to be harder than I thought. I don't think there's room to do it above or below that existing tee. Is there any such thing as a chemical PVC glue solvent that would allow me to loosen those fittings? The only solution I can think of is to cut open the drywall in the bathroom below and start from scratch, but I figured I'd fish for solutions here first before I open too many cans of worms.

Thanks for your help.
 
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