Plumbing Vent Problems in Your House

Your house's plumbing vent's purpose is to remove sewer gases from the drainage system and equalize its atmospheric pressure. Without the vents, our toilets and all other home plumbing fixtures might not be draining properly, can cause unusual noises (like gurgling or belching as and after they discharge), and could be responsible for an unpleasant sewer gas smell inside the house.

A house plumbing system vent is one of those features that may easily become compromised. Some of the most common reasons for the plumbing vent to lose its performance is our lack of knowledge during remodeling, the house age, and / or miscellaneous stuff (including bad luck).

Lets go outside and look at your house's roof; you should be able to see a plumbing vent stack a piece of pipe penetrating the roof surface (if your plumbing fixtures have been located far away from each other, there could be more that one plumbing vent visible above the roof, but at least one should be 3 or 4 in diameter).

It's usually the same material as the rest of your plumbing drain system, but in older homes, there might be 2, 3, or even more types of pipes connected together. If you have a flat roof, you will most likely have to get up there to check your plumbing vents be careful (or even have a professional do it for you!).

If you can see the roof surface and you can't see the plumbing vent pipe you're not alone.

The most common reasons for this scenario are:

  • The main plumbing vent stack starts at the lowest part of your house structure. Decades ago, in older homes, the most common type of the plumbing vent pipe was cast iron - it could settle, shift under its own weight and along the entire length
  • It could have corroded and separated sliding under the roof surface
  • Another possibility is that your old roof has several layers of roofing material, and the vent is still there but its top edge level is the same as the roof surface.
  • Sometimes it may also be blamed on the roofer - if it was too short, he could just go over it with new roofing material; or the plumber just stopped it in the attic or forgot to install it at all

Plumbing vents should be at least 6" above the roof surface. For cold climates, it should be 6" above the snow line (10" above the roof).

So if it's not above the roof, and you do have plumbing in your house, something is wrong and the best place to start searching for the plumbing vent is in the attic. Look for a pipe that penetrates the floor - the area usually corresponds to the toilets locations, kitchens, and other plumbing fixtures in your house. Sometimes it might be hidden under the insulation or simply laying on the attic floor.

You should consider yourself lucky if you can locate it in the attic because sometimes it's just a mystery, and could be an expensive one.

If your vent pipe is where it supposed to be, check the attic periodically anyway; the plumbing vent sometimes cracks, separates at connections, or it could be leaking around the roof surface penetration because of the improperly installed, missing or damaged flashing. If you spot the problem early, it might save you a ceiling repair.

Besides all the common plumbing fixtures, you may also have an ejector pump installed in your house. It might look just like a regular sump pump, but it serves your plumbing fixtures located below the main drain line. The ejector pump well also requires a plumbing vent. The well, its cover and all penetration points should be sealed to prevent sewer gases from penetrating it.

More about plumbing problems in Cast Iron Drain Lines

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Comments 5 comments

Richard Drips 6 years ago

Good info thank!

I also find that it sometimes helps to really flush out any drains - if lightly used it's like sewer water and gas backs up into the trap

- Richard


flash 6 years ago

When sinks or tub in the upstairs guest bath is not used for a week or two there is a sewer smell in this area. The sinks and tub have a gurgling sound when one of the up stairs toilets is flushed. I obviously have a vent problem but don't know what it is. I had a problem one time with squirrels dropping acorns down the pipes on the roof, might have stopped the pipe up.


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Home Maintenance 6 years ago from Illinois, USA Author

If plumbing fixtures are unused for some period of time, water evaporates from p-traps and sewer gases escape into the house. If there's some water left, it might be gurgling when you flush the toilet because of the changing pressure inside the vent stack. However, gurgling is usually a result of a clogged vent stack - you have to check if it's open. Also, run some water through the plumbing fixtures every few days to keep the p-traps sealed.


pat haldane 4 years ago

About 3 years ago the city came into the neighborhood and flushed the sewer system. They said to keep toilet lids down. I had one bathroom where the water was splashed onto the floor. The bathroom that has the odor is cleaned 4 times a week. We came home from a weekend away and the odor was particlarly bad when the heat was on. It is a main floor bathroom. We have 3 vent stacks on the roof. The one bath on the second floor has a toilet that does drain slowly and has had a problem in the unused shower with that pink mold. We did notice a slight drip from the shower head and will fix that but the other problem seems more serious. There is antother bath which is rarely used that has no problems but the water in the toilet seems to evaporate quickly.


Johnf108 2 years ago

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