Thread: Capped pipe in attic

Wasn't sure where to post this thread, so it seemed what I was looking at was a capped PVC pipe in the attic on a newer constructed house (7 yo) so plumbing seemed appropriate.
It appears to be a plumbing vent intended to exit the roof, but is capped.
Has anyone come across this before? Why would they run the pipe & cap it?

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Although I would have expected to see it through the roof, it could possibly be a future for a radon mitigation system.

Plumber capped the pipe to pass the pressure test. There is a chance that there is a mechanical vent that takes the place of this vent (if that is what it is) under a sink. Don't go on the idea that the plumbing will drain slow or there will be a lot of gurgling if it is not vented. I have sealed every vent in my roof as a test and no difference was noted when flushing or emptying sinks and tubs. That said, code requires every trap to have venting, but not every vent has to go through the roof.

Originally Posted by Steven Turetsky

Although I would have expected to see it through the roof, it could possibly be a future for a radon mitigation system.

I agree. They typically install passive radon systems in new houses. If it's for a passive system, even though there is not a fan installed, the pipe should extend through the roof.

But normally, the passive system pipes would pass through the attic in a way that would provide adequate room for a fan to be installed if deemed needed at some point in the future.

The location of that pipe hardly has enough room to install a fan. I suppose you could put a 90 on it and bring the pipe horizontally towards the center of the attic and then turn it up through the roof. That would give you room for the fan is needed.

Originally Posted by Vern Heiler

Plumber capped the pipe to pass the pressure test.

Agreed.

There is a chance that there is a mechanical vent that takes the place of this vent (if that is what it is) under a sink.

Yep ... a *slim chance* ...

Most likely it was just forgotten about and needs to go through the roof.

Just a thought. A roughed-in radon system wouldn't need a cap installed with glue, would it?
I see PVC central vac pipes installed and never used as well. Sometimes they are run thru the attic to the garage.

But I vote with Vern and Jerry, it's a plumbing vent that was forgotten or not needed.

Sometimes original purchasers contract with developer, for example, unfinished basement, or walkout, with roughed in waste, drain, and vent plumbing capped off, (so they don't have to bust the slab later, and open walls above) when the purchasers plan to finish area and install bathroom or half-bath themselves (or act as own GC hiring contractors themselves)at a later date (when they can afford to) - quite common before the bubble. Due to freezing issues the vent may require increasing trade size a foot or so before it emerges the roof to prevent frost or freezing.

Question is, was the bathroom group finished and this step overlooked, or was it never installed.

In my area new construction requires a rough in for radon system. They are supposed to be marked Radon, and capped.
When I have seen them uncapped, there has been a lot of moisture staining on the roof sheathing.

Was there a pipe that actually went thru the roof? If not, then I think you have your answer. The plumber forgot to take it out the roof after they did the pressure check.

Thanks for your input guys, was helpful.

it could also be for running "future" wires from basement to attic. A pre-chased pipe.. look in the basement and you might find the bottom of it. I know of 2 builders in the east coast that offered this as an option to make it easier to add music / data systems after closing.

kurt

Thanks Kurt, nothing was visible in the basement as it was finished. The pipe looked like 6", maybe 4" at least. A little big for wires as well.

Around here the plumbing vents are always black ABS. The size and color looks more like a vent flue for high efficiency furnace but that doesn't make sense. Let us know what you find out.

Originally Posted by kurt jensen

it could also be for running "future" wires from basement to attic. A pre-chased pipe.. look in the basement and you might find the bottom of it. I know of 2 builders in the east coast that offered this as an option to make it easier to add music / data systems after closing.

kurt

Better not "be for running "future" wires from basement to attic." as that plumbing PVC is not listed for use as a raceway for electrical wiring.

Originally Posted by Scot Asher

Thanks Kurt, nothing was visible in the basement as it was finished. The pipe looked like 6", maybe 4" at least. A little big for wires as well.

Too big for residential plumbing vent.
Perhaps a chase for a future swamp cooler or solar panel lines?

waste line for future upstairs bath. remove cap and see if you smell sewer gas.

Originally Posted by Dennis Webber

Too big for residential plumbing vent.
Perhaps a chase for a future swamp cooler or solar panel lines?

I don't agree. A future stack or a future planned auxilliary vent stack from a bathroom group would be increased to at least 3" or two trade sizes (whichever is greater) before penetrating the insulation blanket and at least 12-18" below the roof deck before penetrating the roof for a cold attic in New York (original poster), a far "colder zone" than you are from in mid-Indiana (Indianapolis). For a pre-fit capped off potentially future use (not yet connected to the DWV system) I would expect at least a 4" where it is shown in the photo. A primary stack vent minimum 4" possibly more depending configuration, and increased as necessary to prevent freezing/frost over issues below the roof deck.