I'm not sure what kind of vent this is for, but I'm wondering if its supposed to have a cap to protect from rain.

Sorry for lack of description. I'm completely ignorant to whatever this is.

If it helps at all, I have two turbines on my house plus this pipe. So I know it's not for venting the attic. My guess is its for the bathroom vents maybe?

enter image description here

  • What do you mean by "turbines"? If there is a fan in this pipeline somewhere in the attic, it could be part of a radon mitigation system.
    – Matt
    Commented Apr 11, 2020 at 16:24
  • If you net over the top you may stop mosquitoes. Commented Apr 12, 2020 at 4:57
  • 1
    @Matt By "turbines", I'm 99% positive they're referring to one of these to vent the attic: homedepot.com/p/…
    – Tristan
    Commented Apr 13, 2020 at 15:34

9 Answers 9


Almost certainly a vent for plumbing. It connects to the sewer, so it doesn't need a cap. It's highly likely there's a sink or other fixture nearly below it.

  • 7
    It provides air to the waste pipe so that a vacuum isn't created that would mess with the waste flow and cause air to be sucked through the water traps which would make a gurgling sound.
    – Ack
    Commented Apr 10, 2020 at 23:14
  • 5
    Each house is required to have at least one 3” vent for a toilet. If it’s located above a bathroom, then it’s certainly a plumbing vent and does not require a cover or cap over the pipe. If its not near a bathroom and there’s another 3” vent elsewhere, then it could be a “radon” vent, especially if you live in a radon area.
    – Lee Sam
    Commented Apr 10, 2020 at 23:40
  • 1
    If not required to have a cap, a hood that allow air flow would prevent debris, bird nest, etc to enter and possible block the air vent. Commented Apr 10, 2020 at 23:56
  • 12
    Until I put some 1/4" hardware cloth over our vent pipes, we were getting huge tree frogs in the toilet bowls!
    – fred_dot_u
    Commented Apr 11, 2020 at 1:42
  • 4
    A quick sniff near the pipe should tell you whether it is sewer or radon in a jiffy. Commented Apr 11, 2020 at 12:18

It's a vent pipe for the plumbing it connects eventually to the sewer.

It will catch a small amount of rain but the rain will stay inside the pipe and eventually reach the sewer.

You're probably not supposed to put rain into the sewer but this pipe catches such a small amount of rain that nobody cares.


Actually there is a better chance that it is a Radon discharge pipe roughed in at construction. That pipe is schedule 40 PVC. Nobody uses that pipe for sewer vents. Try to trace it down through the structure a d see where it goes.


They are plumbing Exhaust pipes
You need to leave the end open to allow the air to escape

  • 1
    I reckon it's the opposite - it allows air to be drawn in, when the toilet etc is used. Otherwise the stuff in the pipes would 'hydraulic'.
    – Tim
    Commented Apr 12, 2020 at 15:47
  • @tim Actually, it's both. When a drain is in use, it allows air to come in so that the draining water does not create a partial vacuum and pull water out of the trap at the sink. If the water in the trap was pulled out, any sewer gas would be able to vent directly into the building. When no drain is in use, any sewer gas present in the drain pipes is able to be freely vented to the outside where it can dispurse well above the level where it would be bothersome.
    – user689
    Commented Apr 12, 2020 at 23:43
  • @UnconditionallyReinstateMonica - I'd have thought any pipework tat was directly connected to the sewer would have its own water trap, so sewer gases shouldn't come back through that pipework and into the vent pipe.
    – Tim
    Commented Apr 13, 2020 at 13:16
  • @tim Every fixture - kitchen sink, bathroom sink, tub, toilet - has its own trap. A vent is necessarily downstream of a trap, and a vent may, and typically does, serve more than one fixture. The drain system as a whole will have at least one vent, which will be connected directly to the sewer, but it may not require more than one. The vent itself cannot also have a trap, that would defeat one of its functions. Sewer gas can build up, must be able to be freely vented to the atmosphere.
    – user689
    Commented Apr 13, 2020 at 18:42

Get your ear near to it, and ask someone to flush the toilet. if you hear sound of flush, then its what @Ack said in the comments (it prevents vacuum in your wastewater plumbing).


In my area plumbing vents don't have caps in the sense that they close the end of the pipe. But they do have lead flashing that goes over the pipe and is then worked in with the shingles or other roofing material. Finally a cap is installed on top. The cap is something like an upside down cup with a a sleeve that runs down the inside of the vent. See examples of these products here 1

In your case I would worry about UV/weather damage to the bare pipe. I'm also concerned about the seal between the roofing and the pipe. It looks like there's a black rubber seal but it's hard to tell in the picture.


It's a bathroom vent , connected directly to your plumbing . It does not need a cap to protect from rain however it could use a mesh metal cap to prevent critters from entering inside .


Not a clue where your house is, but in U.K. we attach an air admittance valve, which allows air in to aid draining of baths, toilets, etc. An open tube would do much the same job, but with a one way valve, there's no chance of it getting clogged eventually, or of any smells coming out. So much so, that they are often mounted inside the house, making the plumbing of them so much easier.

  • 1
    You're allowed to air admittance valves in North America too, but only in certain situations (like for a sink in an island counter in a kitchen). Commented Apr 13, 2020 at 12:07
  • This answer is more-so a comment since it does not address the original question. That said, with an air admittance valve, there is a likelihood that the mechanical parts of the valve will eventually wear out (i.e. chance for smells) Vent stacks have no moving parts and they are a great option in areas with no overhanging trees since they are unlikely to clog or wear out over time. Basically, there are trade-offs to both solutions. Commented Apr 16, 2020 at 2:23

This is a plumbing vent. All of the drains in your home have a P-trap immediately under them. When you look under a sink, this is the U-shaped pipe straight under the drain (it looks like a "P" if you tip it on its side). Each of these P-traps "traps" a chunk of water that totally blocks the drain pipe so that gases from the sewer cannot enter your home. Without a vent for every P-trap, water flushing through the drain system can create suction that pulls the water out of a P-trap somewhere in your home, where that empty P-trap will then allow sewer gases to enter your home.

Since these plumbing vents all tie into your drain system, rain water falling down a plumbing vent roof opening enters the drain system and harmlessly travels through to the sewer. Squirrels have been known to occasionally drop delicious treats down these pipes, so that and insects would be reasons to somehow protect a plumbing vent opening.

Your "turbines" cap off HVAC vents, where water falling down these vents wouldn't be so harmless.

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