Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

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Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by kurt333 » Tue Oct 16, 2018 9:12 pm

I have a 3 inch main stack vent pipe, and insulated it with pink insulation all the way up, accept for the final foot or so, where it is in the attic, but noticed when I removed the insulation and vapor barrier that the insulation was a bit wet, and moisture was on the abs pipe above where it was not insulated. And moisture was on the underside of the roof water barrier plastic stuff.
How do I prevent this?
What is the proper way to insulate the main vent stack 3 " abs pipe?
Wrap it with pink insulation and a garbage bag taped over top as vaper barrier?


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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by Shannon » Tue Oct 16, 2018 11:12 pm

Why are you insulating it? I have never seen that done and it may be causing the problem you are having ? They will sweat a little .
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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by kurt333 » Tue Oct 16, 2018 11:38 pm

I think before I did not have it insulated and it was sweating. Maybe I will try it without and see what happens. Warm air in the house hits the cold abs pipe and it sweats?
Warm shower air hits the pipe and condensates, I think.

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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by Shannon » Wed Oct 17, 2018 10:16 am

This is pretty normal for vent stacks to sweat a little when the outside temps get colder.
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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by kurt333 » Wed Oct 17, 2018 11:35 am

So maybe dont insulate it?
The insulation will just get wet anyways if I insulate it?
I have no wall framed around it, the abs pipe is right in the open bathroom showing, maybe why it sweats too because the moist bathroom shower air is hitting it?

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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by Shannon » Wed Oct 17, 2018 1:10 pm

The pipe painted will look better then the pipe wrapped in insulation as well IMO.
Wet insulation looses R value anyways also.
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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by kurt333 » Wed Oct 17, 2018 1:17 pm

Oh sorry, yea I am going to build a box or corner piece to cover the abs pipe, maybe I can show a picture.
I called the plumbing store, they sell a wrap foam for it. maybe I can use that or wrap it with pink.
Hey also, whats the best vent roof seal? Lead or rubber? Do the rubber ones eventually crack and fail?

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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by Shannon » Wed Oct 17, 2018 6:34 pm

Ya a foam cover would be better then batt insulation.
I have not seen a failed rubber one but I don't do much roofing so it may be just a case of not being around them.
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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by kurt333 » Wed Oct 17, 2018 10:03 pm

I ended up using a lead flashing roof cover for the vent stack. The abs pipe was glued in place and sticking out. So was not ideal to try and slip the lead under there after, as I had to bend it up pretty good and then bash it flat after, just barely got it tucked under the shingles, ripped em a bit.
I can see why guys may use the rubber floppy ones, they would flex fit under there easier.

What do you think is best or easiest. To do the interior of my bathroom with drywall or wood paneling and using the wood trim pieces?

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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by Shannon » Thu Oct 18, 2018 8:17 am

“Easiest” comes down to what is your skill level? Drywalling in my opinion is a better option and nicer finish unless you want that country /cottage feel?
Drywalling is not that difficult but does take some time to complete because of drying time beteewn coats. Paneling could be completed in a day and ready for paint.
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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by kurt333 » Fri Oct 19, 2018 3:21 pm

Thanks.
Hey so I wrapped pink insulation around the upper portion of the abs vent stack pipe, and over night, I check it today, and it is just soaked in water more towards the top. I may have had a little portion of pipe near top not wrapped, like an inch section. But I wonder if its still getting wet because I did not wrap it in vapor barrier? plastic garbage bag etc.
Not sure what to do. Dont really want to put all walls on and have it sweating and insulation getting all wet. Maybe that foam cover that wraps around the pipe is the best solution, and its sort of a water proof option.
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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by Shannon » Fri Oct 19, 2018 6:42 pm

So does this pipe sweat as much when not covered?
I ask because I don’t know why you want to insulate the pipe ? What about framing the walls around it and insulate then instead.
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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by kurt333 » Fri Oct 19, 2018 11:10 pm

I am going to try it tommorow without insulation wrap and vapor barrier wraped around it.
I think it did sweat. But I never had a wall built around it yet, and just had the vapor barrier over it. I will try it again and see.
The word on the street, seems to be not to insulate a vent main stack pipe. Most guys say leave it and never heard of someone insulating it. Google search sure does not turn up much...
I thought it was a good idea to insulate it, because I thought that cold air was inside that vent pipe from outside air. So it would be transfering cold to my inside of my house.
But sounds like when you have hot water going down the drains, heat rises up the vent pipe, and when you flush the toilet and stuff, then it sucks in cold air.
You are correct, to build a wall around it, or boxed in section, and then just maybe stick some hard foam insulation to the other side of the inside walls drywall would be good enough. And of course, vapor barrier in that wall too ?
I think anywhere I have pink insulation touching that abs pipe, Im asking for trouble with moisture to be soaked into it.

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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by Shannon » Sat Oct 20, 2018 11:02 am

So I would frame around it and maybe insulate the wall ,more for sound deadening then anything. Vapour barrier should not be on this wall unless it is an exterior wall.
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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by kurt333 » Sat Oct 20, 2018 12:00 pm

Ok sounds good. So insulate it with styrofoam boards? R3 or something.
I dont have much room to build a 2x4 wall, so want to keep it close to the pipe.
But do not insulate on either side of the abs pipe with pink?
No vapor barrier on the boxed section wall covering abs vent pipe? Why is that?

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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by Shannon » Sat Oct 20, 2018 2:12 pm

No if you have room to frame a 2/4 wall around the pipe I would just insulate the wall with batt to reduce the sound of water running. If that does not bother you then for get using any insulation . If that in insulated wall to the right in pictures is an exterior wall it should be insulated and vapour barriered.
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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by kurt333 » Sat Oct 20, 2018 2:57 pm

I dont really have much room to frame a 2/4 wall.
I may do a angled wall from corner to corner right over the pipe.
Maybe I can frame a 2/2 wall. And put foam on inside of drywall.
To the right of that in the pictures is not an outside wall, it is an inside wall. To the left of it is the outside wall.
So you mean, inside walls dont have to be vapor barriers on it? Even in moist bathroom?
I think if I did not vapor barrier all the inside bathroom walls, the moisture would build up especially near the tub surround walls above it. The vapor barrier gets pretty wet after showering.
I did insulate all the inside walls in my bathroom, I think it helps keep noise down, and had the insulation anyways to use up.
Is there a reason to not vapor barrier this wall that I will build covering the vent pipe?

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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by Shannon » Sat Oct 20, 2018 3:56 pm

Vapour barrier are used to stop air and moisture transfer in cold walls where the warm moist air condensates and causes conditions for mould. An interior wall does not function the same. Yes you have moisture in the bathroom but you need to control that by properly venting that moist air to the exterior of the house not trapping it inside the room. Your bathroom needs a properly sized bath fan and duct work to exhaust the moist air outside of your home .

Your feeling of having to insulate that pipe is not needed. If you can’t install insulation for sound reasons at that pipe location for get about it, it’s not that big of deal. For sure do not install a vapour barrier on interior walls.
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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by kurt333 » Sat Oct 20, 2018 4:57 pm

Ok, did not know that.
But i have had it at the insulated stage for a year and showering, so if i did not vapor barrier surrounding walls, moisture would be getting into pink insulation?
thanks i will for sure leave the vent stack un insulated. And just build the wall covering it and see, thanks

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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by Shannon » Sat Oct 20, 2018 6:32 pm

That was fine for the temp. Time but before drywalling you need to pull it off .
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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by kurt333 » Sat Oct 20, 2018 8:58 pm

Really, pull it off? I have insulation behind it on inside walls.
Why can I not leave the inside walls vapor barrier? I am surprised.

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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by Shannon » Sun Oct 21, 2018 9:09 am

No pull it off if it is a interior wall. The drywall painted will keep out the moisture that any bathroom will have. Moisture from bathrooms in an interior wall is a non issue.
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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by kurt333 » Sun Oct 21, 2018 12:00 pm

Is there any harm in leaving the vapor barrier on for my interior walls in my bathroom?
Is it true that vapor and moisture will penetrate wood paneling and get to the back side of the wood paneling and mold and warp it? Even if I have it primed and painted and trim installed.

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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by Shannon » Sun Oct 21, 2018 4:38 pm

No one in my trade leaves a vapour barrier under finished wall coverings on interior walls.
You don’t seem to want the advise I am trying to give . If you wanna leave it then do it, my recommendation is to remove it.
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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by kurt333 » Mon Oct 22, 2018 5:15 pm

Oh yes, sorry, I for sure will remove it. But just wondered why?
My buddy told me, the house has to breath. Is this why?
And the cold and warm rooms need to even out, and cant have a warm room hit a cold room and sweat. Is that why?
Sorry I wasnt trying to sound like I dont want the advise, that is why im here and asking. Just i want to know why, but i can google it, no worries. I will remove the interior vapor barrier, when I am ready to sheet it. Its been at this stage for a year or so, so thought it would get the insulation wet.

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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by Shannon » Mon Oct 22, 2018 7:00 pm

Yes basically interior walls need to breath and circulate.
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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by kurt333 » Mon Oct 22, 2018 9:56 pm

Ok got er.
I will cut the poly off, and tape it at top of ceiling where it comes down.
And behind the tub surround, I dont think I can pull that out. Unless I take the whole tub surround walls apart. Will that be a none issue behind the tub surround, the poly in behind the surround walls?

And also, do you think I should buy a couple sheets of water proof drywall and use the on the ceiling and above the tube surround? Or is that a non issue If i paint it good.
Bathroom is 5'5 x 6'9
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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by Shannon » Tue Oct 23, 2018 8:44 am

Cut the poly off about 3" below top plate and then use acoustical caulk to seal the plastic to the plates and staple in place. Tape will not hold long term when stuck to wood. (I assume this is unheated attic space above the bathroom?)

The entire bathroom should really be the moisture/mould resistant drywall.
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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by kurt333 » Tue Oct 23, 2018 11:46 am

Thanks.
Ok I will go buy some acoustical caulk. It made such a mess last time I used it on the bottom plate when I had to remove poly on floor, so cleaned it up and used tape. But will go ahead and use it if its better seal long term.
It is attic space above bathroom, where the vent pipe goes up. And if you look just to the right of the top of vent pipe, there is actually a small corner gap in insulation where its letting in cold air from the attic. I can feel the cold air being drawn in near top of vent pipe in attic space. I wonder if that is what is drawing in more moisture and cold air? Maybe I should block it off with insulation. And of course if I seal a wall off around pipe, it can then not draw in vacum of air from attic?

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Re: Main Vent Stack ABS Pipe Sweating Moisture Buildup-Insulate?

Post by kurt333 » Tue Oct 23, 2018 11:48 am

Also when I did remove that insulation that was wrapped around vent pipe and poly over it, the insulation still got a bit wet, so indeed its not a good idea.

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