Latest Discussions : Plumbing


07:46AM | 02/24/07
Member Since: 02/23/07
5 lifetime posts
Sorry in advance for this long scenario for a hopefully simple question. The main one is: can there be an almost-steady leak from a PVC vent pipe in a bathroom that's not operational?

We are building a new bathroom on our first floor partially below the footprint of a second-floor bathroom. We had assembled the exhaust/vent pipes using PVC pipe that goes up through the ceiling and on into the attic, where it connects via a Y-pipe to the main vent pipe going out to the roof.

After we had finished installing the ceiling and started work on the finishes, I noticed discoloration in one area. I broke away the ceiling and found extensive dampness at a point just underneath one of the PVC pipe joints. (There are five elbow joints or connections in this area - it's where the exhaust from the shower and sink meet up and then bend upwards to go into the attic). The dampness deeply saturated two pieces of wood - a joist through which we had put a hole that the PVC pipe runs through, and a 2x4 acting as a cat brace between two joists (and which ran directly beneath the PVC pipe, both parallel to the ceiling). I assume some white stuff now on the wood is mold.

Here's the problem: It was really wet - at one point I placed a plate on the floor below because it was collecting a steady drip. But it was intermittent and there was no clear pattern.

Here's a twist: I got up there and wrapped some plumbing pipe tape around the joint just above the cat brace - not cleanly. The cat brace was so close to the pipe that the wrap wasn't tight at all. But since then, I haven't had the leak come back.

Here's the mystery - the bathroom was not yet operational. No fixtures had been attached. I can't figure out how the vent pipe for a bathroom that isn't being used can cause that much condensation or excessive wetness. (This was in December/January). Is that possible?

I wondered if it was possible that there was a leak from the upstairs bathroom but there is no sign of it from the floorboards above nor any pattern I could re-create (leaving the faucets upstairs running or dripping - none of it led to the leak). We even had big rainstorms before and after (rain coming down the vent pipe opening?) - but no pattern.

I think the easy solution is to remove the cat brace, really tightly wrap the pipe, replace the brace, and then move on. But I want to be sure before I close up the ceiling that the leak was coming from the vent pipe, because I don't want it to return after we have all the fixtures in, etc.

So the questions are – (again) can there be an almost-steady leak from a PVC vent pipe in a bathroom that's not operational? Will I be safe if I just wrap up those PVC pipe connections/joints or do I need to re-glue them? Should I keep looking for a leak from the upstairs bathroom?

Thanks for any help you can offer.


11:02AM | 02/24/07
Member Since: 04/25/05
1915 lifetime posts
It is not clear to me where the condensation is.

Normal condensation in a plumbing vent pipe should stay within the pipe.

The other possibility is that a large amount of air is leaking around the holes in the DW and depending on the house contruction from the basement/crawlspace through the plumbing chase into the attic and condensing on the OUTSIDE of the vent pipe.

If that is what is happening you need to seal those air leaks.


12:23PM | 02/25/07
Member Since: 02/23/07
5 lifetime posts
Thanks for your reply - it's a relief to know it is probably not a leak from elsewhere (and now makes more sense).

I will bother you for two small questions based on your reply.

First - when you say pitched away, I want to make sure you are talking up/down angle and not proximity to the fixtures. The pipe joint that is causing me trouble is basically in the center of the room between the shower and sink, where we connected the vent pipes before the stem heads up toward the attic - in parallel/horizontal terms it's not going away from the fixtures. (If by pitched you mean angled upward, I think there is a slight upward slant already that hopefully covers us).

Secondly, I am pretty sure that the plumber who helped us install the vent replaced our cast iron pipe that went through the roof with a PVC pipe, and I am sure that it is exposed to direct sunlight. Is there anything I should do to replace it or cover it?

Thanks again for your help. This problem was driving me crazy.


11:47AM | 04/15/16
I also have moisture on my vent pipe which is leaking into a basement ceiling. I had roofers plumbers out and no one can tell me why I am getting this water. Any help please let me know.


10:27AM | 02/07/17
I recently discovered that I have this same thing happening. This has been going on for years, but it was so intermittent and I was not living in the house for a few years, so I wasn't sure where it was coming from. It is a ranch style home and the leak showed up on the tile in the basement. I took out the tile & noticed the water dripping from the drain pipe in the master bath. I quit using that sink, but it didn't stop. I didn't use the shower in there either. Long story short, I finally found the water was coming down the vent pipe from the ceiling. The vent pipes join together in the attic from two bathrooms. They vent thru a turbine attic vent. This is near the east end of my home that faces south. The vent comes up on the north side of the roof peak. It is so intermittent, only happening in the winter. I have a make-shift water catcher to redirect the water from the outside of the pipe to fall into a plastic bag and then into a bucket under the sink in my vanity on the main floor. I have a fan that constantly blows up from the basement to help keep the floor joist & floor dry. I do not want, nor can I afford costly damage and repairs. Please help me...Thanks!


07:45PM | 09/23/18
Hey guys I been roofing for 17 years ready for the most simple fix. Go into the roof to the pipe flange that’s taking in water from the opening buy an pvc elbow attachment so the pipe opening will now face down so it’s not gonna let water in anymore this will stop any rain water going into pvc pipe and leaking in the attick some times the elbows aren’t glued right so to avoid messing with any of that crap just put a elbow on outside opening of pipe it stops water infiltration completely. Your all welcome


05:07PM | 11/15/19
So I had this problem as well apparently for a lot longer than I realized until I saw the discoloration along a sheet rock seam. After a lot of ghost hunting I found that I had installed a towel bar in the upstairs bathroom and drilled right into the vent pipe going to the attic. Just enough internal condensation and rain found its way to the screw holes and then down the outside of the pipe through the floor cutout and onto the ceiling. Duh.


05:43PM | 11/16/19
I'm a day late and q dollar short but, either snow or ice on roof is leaking in and along side of vent pipe.
Also keep in mind a slow pipe may back up enough to cause vent to be an exit, depending on height.


11:30AM | 12/09/19
have your same problem. never thought about before, but i did know this could . And it happen to me. Have the elbow joints not properly glued and condensation in fining its way through the floor of bathroom. I was furious ,but accepted it as defeat. have to track the water leak and fix it . Its obvious the condensation water will continue. It find itself in the drain system. I hope. End of problem. I hope.

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