3 year old house. There was dripping through the ceiling of the 1st floor. Turns out there is water along one side of a toilet PVC vent stack, but only within the 2nd floor wall (not sure how far up because I haven't torn up all the drywall). In the attic there is 4 ft of uninsulated PVC vent pipe which goes out the roof. Also ruining in the attic and tied in to the stack is a smaller PVC which seems to come from the shower. These pipes on the attic are always dry. Even where the toilet stack goes through the 2d floor ceiling all the insulation around it was dry. So is there condensation occurring along the PVC stack at some point under the ceiling? If so why, and what can I do? I thought about insulating the pipes in the attic. I am in Chicago so it is very cold. The attic is unheated. There us no correlation with rain. Thanks!

Hi Alexakos

I'm afraid that it sounds like you have a leaker there somewhere in the vent stack going further up. Here, there is always some kind of moisture in vent pipes, but it is on the inside of the pipe... if you have water outside the pipe then it's a leak in the pipe/fitting for sure!

If you had moisture showing up on a PVC pipe between floors for any reason then you could be sure that everyone would have similar issues and PVC pipe wouldn't be allowed to be used as drain/vent materials!

Open the wall up some more and see what you find...

Good luck!

Mark

Mass, just asking a question for my own clarification. The water that would be leaking in the vent stack would, I guess, be rainwater from the roof? Is that what you are referring to? I might have misunderstood the post, but it sounded like a second floor problem in the wall which would place it above drain pipes. Is that right, or am I missing something?

Hi John

Alex was very specific when he said, "There us no correlation with rain", so I ruled that out as a contributor... ;)

Water vapor, especially from hot water is almost always present in some form along vent pipes. Here, water vapors rise and then condense on the inner walls of the pipes/vents all day long as plumbing fixtures are used. This condensation, along with the fact that rain water and snow enter the vents is why all vents are pitched back toward the drain system.

In Alexakos's case, a leaker showing up in a 2nd floor vent with no leaker found above in the attic suggests that condensation on the inner vent pipe is showing up at a cracked/uncemented/broken part of the vent system. I have seen it many times over the years.

Hope that made sense!

It did. Thanks. Certainly would make sense that there would be no reason to have condensation on the outside of the pipe.

Yeah, condensation on the outside of PVC or ABS pipe would pretty much negate anyone using the stuff, for sure!

Alex here. Yes, the portion of the pipe in the attic is always dry, even when it rains, so we ruled out leaking from, the flashing. I also forgot to mention that when I cut a small piece of drywall behind the baseboard to expose the sweaty pipe, I took a photo of the pipe looking up, thinking there might be some other supply pipes that were leaking onto it. But there do not appear to be any other pipes of any kind (including of sprinkler system). I was stumped because I considered a crack or hole but I didn't think even a crack in the stack, or a unsealed fitting, would cause a bowlful of drip-water per day. I guess there actually is that much condensation inside the pipes. Also, I had a plumber out before I cut the 2nd floor drywall and he did not mention that possibility. Then I spoke to him before this post and he did not mention it. I will let you know when I do some more cutting. Thanks for the help!

Once the pipe is exposed, wrap some toilet paper around the seams of the fittings and down along the pipe in 1 foot increments. In this manner the leak and its location should be revealed pretty quickly... ;)

Thanks for the update!

Also ruining in the attic and tied in to the stack is a smaller PVC which seems to come from the shower.
How small is smaller?

Do you have a furnace in the attic?

Hi all. Found the leak; slow drip from a pipe fitting near the attic penetration. There does seem to be some purple glue around there but it's definitely not sealed well enough. Can I repair with silicone or what? Do I need an expert for this? Of course because of the location there's no way to remove it and redo it... THANKS ALL! Mystery solved!

Hi Alexos

I don't think silicone will work for you here as there is always water present in the pipe/seam/joint, so the silicone wouldn't cure and the leak would probably just show up again, surely after all repairs were made, too!!

One thing you could try would be to clean the seam at the joint up real well with a PVC primer/cleaner and then push some PVC cement up into the joint seam... that would probably work pretty good.

However, if you want the best result here, I would suggest that you clean the seam at the fitting real well (isopropyl alcohol) and then use some sand cloth to rough up the pipe and seam area a bit, and then apply some PLASTIC EPOXY in the joint seam using water to smooth the putty out! Here, the water in the pipe will not stop the chemical reaction from taking place in the plastic epoxy and it will set off and cure to a really good repair!

Good luck!

Mark