Hi
I have a 3 inch copper wet vent stack in a 1960s bungalow with a basement. Live in Canada, was -10c over night last night
I’m redoing the basement, and noticed that there’s condensation on the pipe in the basement right below the floor above. It’s about 6 inches down the pipe where the arrow is on the photo
From there down it hits a Wye for the bathroom toilet and it’s fine
I’m insulating the the rim joist and walls with 2 inch XPS, sealed around the edges with spray foam, and the drain vent passes from the inside of the basement wall into the wall above, so behind the drywall
Should I be insulating the vent stack all the way down to the floor? I was going to box in the pipe on the warm side of the basement wall
The basement walls are having r14 batts in steel stud after the XPS is on
Thanks
Mark
Replies
Seems the vent pipe is loosing heat inside the wall above to the point that the surface temperature under the floor above is under the dew point. (in winter conditions)
The larger pipe has enough heat to remain at a temperature above the dew point.
I would wrap the smaller diameter vent pipe with a product designed to address pipe sweating, but leave the larger pipe on the inside of your new insulation envelope.