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I'm installing a closetmaid shelf in my closet in a 2nd floor bedroom. I was drilling behind drywall and on one of the holes I marked I hit some kind of plastic. I'm not sure if its a wall or pipe, but it is white in color (I've already shaved off pieces of it with the drill). I'm confused because I used a high quality stud finder and it shows nothing there. Well, the plastic is technically 1/2 inch behind the drywall so the stud finder possibly missed it (maybe).

This hole I drilled into is close to the edge of another wall (a wall of one side of the house). The plastic is adjacent to another stud, though. Doubtful that it might be plumbing (subjective) since the side of this wall is not shared by any walls of a bathroom. The wall is directly below an attic and the floor below are just regular living rooms.

Any idea what I drilled into? and whatever that may be, would it be safe to drill into ?

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    It's never safe to drill into an unidentified object. Stud finder will not detect PVC pipe, which is possibly what you drilled into behind the drywall. I'm finding it difficult to envision the layout you describe, but PVC can also be used for plumbing your A/C's evaporator drain pan and conveying the water outside the home. – user56530 Aug 28 '16 at 3:27
  • How do you know its PVC and not (vapor barrier for example)? – Narcotixs Aug 28 '16 at 3:38
  • I don't. Would it make a difference? Puncture a vapor barrier and you could create a path for mold growth. Same if you punctured PVC pipe containing A/C condensate. – user56530 Aug 28 '16 at 3:44
  • Well from what I've been reading, it's very rare for a building to have a problem caused by vapor diffusion and very little gets diffused through drywall almost where many arguments support that a vapor barrier isn't needed. – Narcotixs Aug 28 '16 at 3:58
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    I'd guess a PVC plumbing vent, but without seeing the layout of the home it's difficult to say. At any rate, I definitely wouldn't keep drilling, until I knew exactly what it was. – Tester101 Aug 28 '16 at 12:22
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No, it's not safe to drill into something unidentified.

White PVC is most commonly used for waste water (and vents, which are connected to the waste water lines but carry sewer gas to a vent the roof) and central vac. Schedule 20 is used for central vac and is much thinner than the Schedule 40 used for plumbing

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It's also possible it's a conduit run for future use, eg running wires from the basement to the attic -- which may or may not have something in it now.

Now that you've hit it, you really need to open up the drywall there and figure out what you're dealing with, repair it, and then patch up the drywall. I'd suggest just opening a relatively small hole first to inspect it, then cut a bigger one if needed once you know what you need to do.

If it's central vac or plumbing, you'll have cut out the damaged section and replace it. If it's small hole, you may just be able to cut just that tiny bit out and replace it with a single coupling. For a bigger hole you'll have to replace with two couplings.

You can probably post back with a picture of the damage and describe what you see inside and we can provide better insight into what it is and how to fix it.

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