Roof leak that's not in the roofing: watch out for galvanized plumbing vent elbows

Home built 1938.
Flat roof.
Galvanized plumbing vents go up the exterior walls, make a 90 degree turn, then another 90 and exit the flat roof, pretty typical design.

The problem turns out a bit subtle. The vents are open up top, and rainwater and dew is expected to enter and drain into the sewer. But if you imagine a galvanized elbow in cutaway (I can’t post images), you’ll see it always has a little shelf the depth of the connecting pipe wall. It’s inherent in the design.

Thus, for 77 years a little bit of water sat in each elbow, until maybe it dried out in summer. That elbow got thinner every year until finally… a slow drip perfect for attracting termites but not a big enough leak to call attention to itself.

As for what to do about it, I open that to the forum.

Keywords: old house plumbing DWV drain waste valve leaks inspection.

The average life expectancy of galvanized iron piping under normal conditions is 70 years you have 7 years of grace on your 77 year home replace it and be thankful for the 7 years:mrgreen::smiley:

It’s one of those subsystems that’s either hideously expensive to retrofit, or as cheap as a $20 Air Admittance Valve.