Hi everyone, hoping to find some advice.

Here’s a link to a video, which shows the situation of the PVC (edit: it actually appears to be ABS, see link to pic added below) vent pipe sweating and dripping.
[imgur.com]

We bought this house this past summer, so it's our first winter here. There was an indentation in the insulation that looked like the prior occupants may have had a bucket or something to catch water, so this may have been an existing problem that never got addressed.

(1) My understanding is that since this is a vent pipe, it shouldn’t contain any water—unless there’s a leak around the roof exit. I don’t think it’s a roof leak, though, because as far as I can tell there’s only a leak at this particular arm, and the stack also includes the vertical section that goes straight down, so I figure water would follow that route instead of running over to this elbow. (As far as I can see the other arm, it looks dry over there.)

Also, the dripping doesn’t look like it’s coming from inside the pipe. Though it is dripping at the joint, it’s also dripping from the body of the pipe itself. (I’ll note that this arm is not well supported and appears to have sagged below horizontal, so the slope runs towards this elbow. Is this arm supposed to be horizontal?)

(2) If it’s not water from inside the pipe, it’s condensation. In which case, the solution is either insulating the pipe to keep it from getting so cold, or cutting off the source of the hot/moist air, and I think the second makes more sense for me.

The big suspect for hot/moist air is: The attic access is from a poorly sealed piece of wood that’s located right next to the shower. [i.imgur.com]

Like many people, we had a cold snap the past several days. When I first went up into the attic this morning, that pipe had a bit of frost on the top, and the dripping was slower.

The shower hasn't run today, but best guess is that the showers over the past couple of days sent humidity up to the attic, some of which froze on the bitter cold pipe. Temperatures are well over 32 now, so the frost and humidity on the pipe is unfreezing and dripping from the lowest point on this arm.

(3) Short-term plan is to keep an eye on the dripping; if I'm right, it should slow down as the frozen moisture drips off.
Long-term plan is to put a plastic seal over the attic entry so that moist shower air can no longer freely get up there. I’ll put a zipper on it so I can have access to the attic.

Hoping to hear any thoughts and see if this is something I need to call a professional for.

Thanks a bunch. Happy holidays and happy new year!

Edit: picture of the pipe [i.imgur.com]



Edited 2 times.

you have a COPPER vent pipe

said pipe should be pitched downwards towards the interior fixtures served so no water can accumulate internally

the el from which the drip is occuring 'seems' to be a 'low spot' possibly leaking from a 'puddle' within the pipe


copper WILL sweat more than PVC


the vent piping 'should' contain warm moist air which is condensing internally and running back to and draining into the fixture piping


IMO: fix the pitch issue, insulate the copper VAPOR TIGHT, fix the access panel air leakage

==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

Thanks bernabeu.

When I lifted the el by hand, I heard a decent amount of water slide back down. So it seems like maybe the pitch is the big problem. I didn't realize so much water could 'sweat' through if it pools there.

The slope seems pretty negative right now... I'll see if I can at least get it horizontal.

Also, I was wrong about it being PVC; turns out "ABS" is written right on it. If it is ABS rather than copper, would you still insulate it?

it is not sweating thru, it is leaking.
take care of the leaking el and no insulation is needed.

so for now put the pan back under it and deal with it when the weather is nicer.

yes, it IS ABS - at first glance it was shiny like copper

packy is correct, seems to be an actual leak


fix the leak and the pitch

==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

Thanks so much fellas, I appreciate your help. Happy new year!



Edited 1 times.