Vent stack leak advice

Old 11-27-16, 12:41 PM
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Vent stack leak advice

Please give me some advice on an intermittent slow ceiling leak. Drips at night, no rain for days.

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I've tracked it down to a plumbing vent stack in the attic. As you'll see in the picture, the previous homeowners also tried to address this problem. It appears to me that this is condensation leaking at the pipe joint from inside the vent stack. Someone has used clear silicone or something in an attempt to seal that joint in the past. The red circle in the photo indicates where the moisture/dripping seems to be localized.

One thing I noticed is that the horizontal pipe is sloped toward the elbow joint, not toward the sewer side. Wouldn't this cause condensation or rain water to collect at that elbow and eventually leak out?

If so, the stack has some play in it to push it up through the roof and force the horizontal pipe to slope away toward the sewer. I thought a simple fix might be to push the stack up through the roof opening an inch or two and place a block of wood between the joist and the pipe to hold it in place. However, when I push the stack up by hand, some daylight shown in around the boot/roof opening. Do I risk damaging the roof or boot around the vent stack by doing this?

Any advice? Thanks!
Old 11-27-16, 12:52 PM
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Yes, the vent needs to drain, and it needs to be sloped properly. Can't see the condition of your roof boot but they commonly deteriorate, leak and need to be replaced from time to time. You could easily cut out and repair the leaking elbow. You "could" try to repair it by slopping glue around the outside... if it is pitched properly it might work, might not. Probably won't work if they already tried to caulk it. You "could" also clean all that goop off and patch around it with jb waterweld, but cutting out and replacing it is the right thing to do.
Old 11-27-16, 01:09 PM
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100% sure it was even glued in the first place?
I'm not seeing any primer stains on the pipe.
Old 11-27-16, 06:28 PM
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I agree with Joe. I have a feeling it was likely not glued. I wouldn't try to glue it in place, it may work, but may not. I would take the whole section apart and re-pipe, use purple primer, and cement to put it all back together.

As XSleeper mentioned, you should definitely check the boot on the roof and ensure that you're not getting any leaking dripping down the pipe too.
Old 11-27-16, 07:37 PM
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Good advice, thanks folks.

The boot is new and the exterior of the pipe from the roof down is completely dry. I also noticed the lack of primer stains but the joints are indeed welded. The horizontal section sloped down toward the leaky joint nearly two inches; pretty sloppy.

I just cut it out and replaced with a proper slope. It was easy enough. No dripping so far. We're supposed to get a couple inches of rain tomorrow. I'll watch it for a couple days before repairing the drywall.
Old 12-12-16, 01:10 AM
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try to do something like this:
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