Our house, built in 1988, has a leak in its vent stack where one vent line tees into the vertical "main" vent before the main vent goes through the roof. The leaking tee is about 6 to 8 feet below the roof.

Normally there is no problem with the vent stack (no smells, etc.), but when we get a heavy rain, there is water leaking through a seam in the drywall in the upstairs hallway. During a recent rain, I went into the attic, found the leaky tee and wrapped it in electrical tape. This stopped the leak, and the hallway wall dried up.

After the weather turned nice again, I ventured onto the roof and ran a 20 foot snake down the vent stack but didn't encounter any obstruction.

What are your thoughts on putting a couple of 90 degree street elbows together to form an inverted U on the vent stack outside to keep rain and other debris from getting in the vent?

I know I should find the root cause of the water build-up in the vent stack but, other than the leaky tee, there don't seem to be any problems with the vent stack.

I appreciate your help.

Knowing the material the pipes are made of would have helped. I would have sugested recaulking the lead joint or a metal epoxy if the pipes were cast iron or grouting the leaky joint with epoxy if PVC or ABS but your idea is unique and would work just fine. Congratulations for coming up with it. Regards and have a happy forth. Tom

Thank you for your quick reply.

You're right, I should have mentioned the vent stack is made up of black ABS (?) pipe.

Actually, the rooftop is a lot easier to get to than the leaky tee in the attic, so I'll try the inverted U and see what happens.

Thanks again.

A rooftop U is not the correct way to repair a broken pipe or joint in your attic.
What you are forgetting is that if water can leak out , so can sewer gases.
This is extremely unhealthy and potentially damaging to your attic.
Fix the joint by either replacing the pipe section or re-sealing the joint where the leak exists.