Our house has a 3 inch PVC pipe running from the basement to an unknown location in the house. It has no T or Y junctions connecting into it. It does NOT go into the attic. The only pipe into the attic is the sewage release one.

We had a company come out and check the attic and they said there is no continuation of the pipe to the attic so they are unsure what it is. They said the original builder could have built it up to the attic and it’s under the insulation but there’s no way to know without extensive checking of the attic. They told us to contact the home builder for the blue prints to verify what it is because they don’t want to cut anything without knowing. They also said that if they were to installed a new one along side the unknown pipe that it could suck air from the attic into it if it were a passive system.

I contacted our home builder for the blueprints but they are refusing to release them to us.

So what are we supposed to do? Radon guys said they won’t touch it until they know and there is no way for us to find out what it is.

Unknown pipe

  • 2
    what is your specific question?
    – jsotola
    Commented Jun 14, 2023 at 16:23
  • 3
    Your local building department might have a copy of the the blueprints. They needed them to issue the building permits.
    – crip659
    Commented Jun 14, 2023 at 16:53
  • 3
    The pipe is visible in the basement ceiling. It turns upward and goes through the subfloor at some point? Surely you could measure an offset from stairs, an exterior window, or other reference and use that to determine in which upstairs wall the pipe may lie. 3" pipe doesn't run horizontally in a normal-thickness wall, so if the indicated wall is "normal" thickness, look for signs of the pipe in the ceiling above that wall. No need for extensive searching in the attic; simply measure to the area where it could/should be.
    – Greg Hill
    Commented Jun 14, 2023 at 19:12
  • 1
    The homebuilder doesn't want to give you the blueprints, that's fair. Have you asked if they would they be open to answering a specific question about this pipe?
    – spuck
    Commented Jun 14, 2023 at 20:16
  • It certainly fits the profile of a passive radon vent, other than the part where it doesn't come out of the roof.
    – Ecnerwal
    Commented Jun 15, 2023 at 0:16

1 Answer 1


We can reasonably assume that it's not for drain plumbing since there's no cleanout near the slab. I assume that there are no branched pipes connecting to it, either. Therefore, it's a matter of locating the termination. Here are a few ideas.

  • Make a nice square cut in the pipe at the furthest upward accessible location. You can later repair this with a shielded no-hub connector (or two if you can't move the pipe enough to offset it for installation) and not sacrifice the integrity of the system.
  • Run either an electrician's fish tape or a borescope (or a borescope on a fish tape) up the pipe from the cut. This may tell you how far the pipe goes and you may see clues as to its path.
  • Have a helper or two listen at various points in the house while you do this. They'll probably be able to hear the clacking of the device as it travels the pipe. You could also send a sharp sound up the pipe to assist with this.
  • Attach a source of forced air, such as a shop vacuum in reverse, to the pipe. This will tell you whether it's capped or open. If it's open you may have audible clues as to the termination point, and if you have a helper observing the attic you may see it puff insulation out of the way.
  • Downvoter, I'd love to hear your thoughts on the subject. Where have I gone woefully astray here?
    – isherwood
    Commented Jun 14, 2023 at 18:15

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.