Leaking Waste Drain Stack

I've been trying to locate a leak that originates in the attic when it rains. I finally found the problem. The waste drain stack comes out of an interior wall, runs horizontally for about 20 feet, then turns vertical again up through the roof. The problem is that the horizontal run is slightly sloped away from the interior wall. Rain enters the vertical and has no where to go. The pipe is leaking from the joint of the 90 degree ewhere it connects to the vertical pipe.

Can I simply raise the horizontal pipe with a piece of wood so that it drains back to the drain system ?

I assume it would be better to replace the leaking elbow but there is no flooring, lots of insulation, and tight work space so I would rather not get that involved.

The vertical pipe seems to be loose at the top where it goes through the roof. From outside the house the pipe is metal so I assume there is some sort of a fitting. Is it supposed to be loose ?

Thank you for your help.

This sounds horrible. I doubt the elbow is leaking but that the flashing for the stack has deteriorated (or is missing) from the roof. Are you sure rain is not dripping down the outside of the pipe?

I just checked it again. There is no sign of leaking at the roof. No water stains. The vertical pipe is not wet. It only leaks when it rains really, really hard. That makes it really hard to track down.

Normally there is only air in this pipe so that's why I thought I could change the slope slightly.

leak

If the fitting is leaking but you change the slope, you will eliminate the symptom, but the pipe can still leak.

So... what is the remedy for this? I lately have the same exact problem. Short of tearing up the floor above where pipe passes through to basement ceiling? Or is that the next step? I have had the roof checked. The water that drips around pipe is clear , not waste.

Remove the 90. Fix the slope on the horizontal run so that the water drains back to the stack. Shorten the vertical piece that protrudes the roof, then reinstall the 90.

Don't like uncomfortable work environments? Call a plumber, we eat tight spaces for breakfast. Sounds like a 2-hour job.