Fixing leaking PVC pipe joint

danielj_2009January 15, 2012

Hi. I've got a 2" white pvc vent pipe running through my attic. I started noticing water building up behind the paint near the ceiling, so I went to the attic and cut away some spray foam insulation to see what the problem was. It turns out the pvc joint is dripping water. (at least it wasn't a roof leak). The problem is that the piping is in a difficult spot to reach and I'm trying to find an alternative to cutting away all the piping and redoing it. Is there a product out there that can be smeared on the leaking connection that will be a permanent fix? When the problem is fixed, I have to close up the area and spray with foam insulation again, so it isn't something I want to come back to in a few years.

Any suggestions?

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If it is difficult to get to and you can not replace it, you might want to try the stuff they advertise on TV. It is a spray rubber coating that water proofs gutters, doors etc. I can't recall the name and I dont even know if it works but it might be a worth a try

    Bookmark   January 15, 2012 at 1:14PM
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The way to not have to worry about it in the future is to re-glue it properly. Do you know if the joint the leak is coming from is actually glued? Sometimes installers fit piping together and miss a glue joint in the process.

It may not be that much work to do it right. Can you post a picture?

    Bookmark   January 15, 2012 at 5:02PM
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You might try that spray on stuff they advertise on TV for $19 a can, and when that don't work you might try duct tape, followed by bubble gum, elmers glue and whatever other fly by night fix you can come up with, but I seriously doubt if any of those will address the real problem. I fact, I have very serious doubts if the joint in question is the real cause of your problem.

First off, its a vent pipe and there is no appreciable amount of water present in a vent save for some condensate that forms on the inner walls of the pipe as the air exits. If the pipe is vertical that condensate will cling to the inner walls of the pipe by surface tension and when it comes to a joint it simply continues on down the inside of the pipe. (There is absolutely no pressure that would force the liquid through the tight tolerances in the joint).

On the other hand, if condensate is forming on the exterior walls of the pipe it will also cling to the pipe by surface tension as almost an invisible film until it comes to the raised edges of a fitting, then it will form droplets on the top of the fitting giving the illusion that the joint is leaking.

On the other hand, if the pipe is a horizontal pipe it could have an improper pitch and water is being trapped in a puddle at a low spot, then leaking through an unglued or improperly glued joint. If that is the case the joint in itself is not the whole problem. You must correct the pitch or water will continue to condensate and eventually obstruct the vent.

However, if you have an appreciable amount of water dripping so that it is causing a mark on the ceiling below, the problem most likely is a roof leak, only it is concealed from underneath by the foam insulation and it is migrating across the insulation and down through where the pipe penetrates the insulation.

    Bookmark   January 15, 2012 at 9:10PM
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Thanks for all the replies. After further consideration I'm going to try and cut out the pipe with either a small hacksaw or one or those wires that cuts through PVC. I'd sleep better knowing the pipe was replaced properly.

lazypup: It is definitely a PVC leak. The vent pipe comes down from through the roof and then makes a horizontal run. The leak is at the end of the horizontal run just before it goes vertical again. I don't think it is a coincidence that the leak started when we started getting some cold weather. It'll be a simple fix if I can manage to cut out the existing pipe.

Thanks again for the comments!

    Bookmark   January 16, 2012 at 1:49AM
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It still sounds like a roof leak, to me. Before you cut any pipes, test the roof jack with the garden hose.

From inside the attic, can you see the pipe go through the roof? Is any daylight visible around the roof jack seal?

Wrap some paper towels around the top of the pipe, as close as you can get to where it goes up through the roof jack. Then go up on the roof and spray the roof jack and pipe real good with the hose. Then go back and check for water on the paper towels. If it is the roof jack, that is an easy fix.

I spend a great deal of time chasing leaks. Roof leaks are the most elusive. The water never just drips straight down. The surface tension property of water allows it to travel horizontally for great distances, especially when there are things like pipes, ceilings, and insulation for it to work with.

    Bookmark   January 16, 2012 at 10:37AM
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aidan - Thank you very much for the warnings about water moving around unexpectedly. I can say definitively this is not a roof leak. The biggest clue is that the leak continues even when there is no rain. I have checked the pipe around the roof opening and it was dry while at the same time the pipe was dripping. I can see the actual drip coming out of the pipe.

On another note, I had a leak from rain above our French doors awhile back, but then it stopped. I think it stopped after I hydroblasted the windows and saw a bunch of debris/leaves coming out from around the door weep holes. I never pursued why the doors were leaking (from above the door frame) but have to think something was backed up. Something tells me I'll have more opportunities in the future to track that one down. :)

    Bookmark   January 16, 2012 at 11:18AM
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"The biggest clue is that the leak continues even when there is no rain."

You should keep looking very carefully.

Vents do not normally have any liquid in them.

The warm moist air can cause condensation to form when it get to the cold end of the vent outside the attic, but that should be a very small amount.

The only time a roof vent should have any water in it is when it rains and a tiny amount is collected in the open vent.
Other than that vents are normally dry, especially in an attic with no other bathrooms above them.

    Bookmark   January 16, 2012 at 3:58PM
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You have a bigger problem than a poorly glued joint. If you insist that it is the pipe leaking then the pipe is not properly pitched. There should never be enough water in a vent pipe to cause a leak as you describe. It sounds like the pipe is pitched to collect water which could eventually lead to a non-working vent if it collects enough water. Can you get a level on the pipe? The bubble should go to the roof side of the vent line...

    Bookmark   January 16, 2012 at 9:39PM
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I went to make the repair and realized I have 1.5" pipe, not 2" (stupid). I was originally surprised at the amount of water accumulation, but I'm not well versed on how much condensate to expect. I have a cup underneath the drip right now, and collected maybe a few ounces in a 24 hour period.

I can tell you this: After coming down from the roof, the line goes horizontal and from visual inspection appears to be pitched in the right direction. After maybe 8' of horizontal run there is a short 90 elbow, also horizontal. Then there is a short, say 1" section of pipe connected to this 90. This 1" section is mated up with a pvc coupling ring. This coupling is mated with about another 4" section of pipe until it meets a 90 oriented vertically. The drip is between the coupling and the 4" section of pipe. It appears they glued the wrong length pipe and then used a coupling to fix the problem. There must be a small gap between the coupling and the 4" section of pipe where the water finds a low spot.

My plan was to cut the long 8' run of pipe just upstream of the horizontal 90, and also cut the 4" section of pipe after the leak. Then put new couplings on the existing pipe and connect a new horizontal 90 with new 1.5" pipe.

I've done a number of pvc glue jobs and one thing that always bothered me: When I dry fit the pieces to check spacing, I can only twist the various parts together so much. When I apply glue the pieces then slide together tighter due to the lubrication, and then my spacing is off a little. I'm reluctant to push the pieces together less than the full amount when lubricated for fear of getting a leak. Do you oversize your piping sections a little to account for this, or just leave a little slack with plenty of glue? I haven't had any pvc leak on me yet, but always struggled with this. I thought maybe to glue everything together except the last coupling, and then dry fit that last connection and cut down the pipe as needed to make the final fit.

    Bookmark   January 17, 2012 at 2:23AM
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If a vent line is pitched correctly it should never have more than a light film of condensate on the inside of the pipe wall as a worst case scenario. The fact that you have collected a few ounces in 24hrs confirms that the line is pitched incorrectly and that condensate is forming a puddle at the low part of the line.

All horizontal portions of a vent line MUST HAVE a minimum of a 1/4" per ft pitch downwards from the roof opening to the vertical riser dropping down to the drain so that any condensate that forms in the line will quickly flow down to the drain.

    Bookmark   January 17, 2012 at 10:36AM
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I use a tape measure to get the exact measurement and then I usually subtract 1/8" just to be sure it is not too long.

Is it raining while you are doing this? If not you should have negligable condensate, not a few ounces....

    Bookmark   January 17, 2012 at 10:37AM
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I'm thinking whether there is a pitch or not, there will still be a little standing water and a drip in that spot if the coupling isn't pushed together completely. The short section I'm looking at doesn't look pitched horribly wrong, but I suppose there could be a little standing water there before the pipe goes vertical again. I'll know more when I cut the old section out tonight.

    Bookmark   January 17, 2012 at 11:36AM
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"an alternative to cutting away all the piping and redoing it"

Cut the pipe in straight sections that are large enough to be glued back together using a 'no stop' coupling.

You should be able to re-use the pieces, and the additional coupling will help provide some extra length for the uncemented joint so it can come up tight.

A good thick application of cement can also ensure the joints are sealed even if the pipes do not fully bottom out in the hubs (not the best technique, but it is just a vent line).

    Bookmark   January 17, 2012 at 3:34PM
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Smear some PVC glue over the leak and let dry,then repeat and youll be fine.

Here is a link that might be useful: flexible bellows

    Bookmark   September 17, 2012 at 12:41AM
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Adding aditional glue to the joint does absolutely nothing but waste glue and the flexible elbows you suggest are not even made for PVC.

I suggest you use your time to study how to do the job, rather than sit here trying to convince us you have any inkling as to what should be done.

    Bookmark   September 17, 2012 at 9:59AM
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This is a pretty old post. For the record, I ended up cutting out the bad section and replacing it with new PVC. Problem seems to be solved.

Thanks for the suggestions in this forum!


    Bookmark   September 17, 2012 at 10:20AM
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Glad to hear it was solved. I know I don't sleep well til I do a proper fix.

I was curious, I'd seen a leak stopping kit in a wholesaler, but I also came across this link: I don't know how effective it would be, since you're relying on the solvent to soften everything enough to re-form the joint, but with the suction on it, you never know. Mind you, if you can get to the pipe to block one end, and apply suction to the other, you might was well replace the pipe, as you did. Mind you, you can't always get to the pipe to do it.

When I was at a plumbing wholesalers, I saw a thin collar designed to stop leaks, it was pressed up against the joint or fitting and cemented into place. Interesting idea but for the truly desperate, if water's getting that far. You'd be better with a ring of JB water-weld, the plastic putty stuff.

Still no substitute for remaking the joint. For the record, the issue of not getting the pipe properly pushed up to the stop is often caused by failure to de-burr the cut pipe end - you need to remove any residue left from cutting the pipe, burrs etc.

Here is a link that might be useful: Fixing leaking pvc joint

    Bookmark   September 23, 2012 at 2:29AM
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