My home is a single story but with a full basement. The attic is a basic "A" roof. The home looks like a double wide but it's a frame home.

I have a drip problem in the basement directly under the only bathroom in the house. I had to tear out the entire vanity to get to what I thought was a spigot leak in the wall behind the vanity. I did not find a spigot leak. Instead, I found water and mold all around a joint in the 6" PVC vent pipe in the wall. The water appears to be coming from above, hitting the joint I just described, then continuing down the outside of the pipe into the basement where it then drips onto the floor.

I have traced the water from the basement below, up to the vent pipe joint in the bathroom, then further up into the attic. The pipe then makes a ninety degree turn in the attic and heads six feet towards another 90 degree turn and then out the vent in the roof. It is at the first 90 degree turn above the bathroom that water appears to be emanating.

No water is on the vertical vent pipe from the roof, nor on the six foot or so of PVC pipe leading over to the pipe coming up out of the bathroom. I see no leaks at the vent in the roof nor in the roof above the first 90 degree turn from the bathroom below where the water first appears. But at the joint above the bathroom, I see water appearing then running down through the bathroom wall along the outside of the pipe and into the basement. It is a direct line of water starting in the attic then dripping straight down, through the bathroom wall and into the basement. This is occurring when no rain is present.

I am beginning to think that this is all condensation. It's not rain, and there is no water in the vent pipe (unless rain water is getting in it and then getting stuck due to the horizontal pipe sloping incorrectly and then leaking out of the joint above the bathroom) but that's a lot of "ifs"...

I am considering moving the vent in the bathroom wall over closer to the center of the house so it is more accessible. Right now, you can hardly get to it because the roof slopes to a close in that area. By moving the entire vent pipe in the bathroom more to the center of the house (and to the attic access hatch), I could at least GET to it in the attic. I would also then be sure the pipes were all glued right and sloping correctly.

But what then? How do you stop condensation like that? I can't put the (only) bathroom back together again if water is still dripping down the brand new pipe, through the wall and into the basement. I forgot to mention that the basement is also an apartment, and the kitchen is directly below the drip. It's a mess.


Thanks in advance for reading this and trying to help me.



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You really can't stop internal condensation, that's why vent pipes need to be installed flat or pitched back, to drain out any accumulation. Sounds like just a bad glue joint or cracked pipe.

The water is not coming from inside a pipe. It's outside the pipe. How do you stop that?

Condensation on the outside of the pipe would indicate excessive moisture in the attic and you would see it along a large area of the pipe. Internal condensation is from hot water draining into the drain piping and the steam rising up inside the pipe. As the steam cools, it turns back into water and collects on the inside surface of the pipe. It then runs back down towards the drainage piping and a bad glue joint/cracked pipe can allow that water to exit and run down the exterior of the pipe.

You have taught me a ton. Thanks for the precise information. We have REALLY hot water (and I like that) but I'm sure it is causing this problem. I think you have nailed it with either one scenario or the other... because it's got to be condensation... and I think it's the second one. There is quite a bit of piping in the attic and water is only appearing at once spot, not all along the pipe, so your first scenario does not look like the culprit.
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I think the solution is going to be relocate the attic piping so it is easy to get to and will then have NEW plumbing. I will locate it off to the right of the vanity in the bathroom and put a panel there so I can see problems if they begin to reoccur. But I think you are right about the water running back towards the drain in the attic, then finding a cracked ninety where it appears to be leaking down the outside of that drain pipe and into the rest of the house.

I'll keep you posted on the final results. And thanks so much for your time !!



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Wrap some tissue paper around the two 90s in the attic then duct tape over. Wait a day and see which one is wet?

Will do !

I am assuming that it is normal for condensation to form inside the pipe during hot water events and cold days in the attic? Then that water just runs out the drain like it's supposed to, right?

But if there is a bad joint (which is what I think we have determined) the condensation water inside the pipe will leak to the outside of the pipe and do damage as it runs downhill (which I think we have now assumed is happening).

Everything points to that. It can't be rain. We haven't had any. So that discounts a leak in the roof too. And it can't be water lines. They are none in the attic where the water is emanating from. There are none in the attic period.

I'm moving the pipe in the attic to a more reachable location up there, and putting all new plumbing in place at that time. I'm also going to leave an access door in the bathroom that is not behind the vanity so we can keep an eye on this in the future.

Another thing I noticed is that ALL the insulation in that part of the attic has been moved to the side. There is NONE on the attic floor where all these pipes are located. I'll fix that too.

Regarding condensation INSIDE the pipe, that is how hot vapor in a vent pipe could rise up to condense and leak out above all waste connections.

Since you now have access to the entire pipe, try Sum's tissue paper suggestion at multiple points along the pipe all the way to the top. Sometimes it is difficult to see small amounts of water intermittently flowing down the outside of a pipe. If you can find the leak, you might be able to save some money and effort replacing everything.