Plumbing vent FAQs:

Frequently asked questions & answers about plumbing vents: what is a plumbing vent, how do we define the types of plumbing vents, how is a plumbing vent installed, what is an air admittance valve, what is a wet-vented drain, what are direct-vented fixtures & what are the distances from plumbing fixtures to plumbing vent stacks?

This article series defines plumbing vent system terms, distances, and functions, and other specifications and code requirements. We explain how plumbing vents work on buildings, why plumbing vent piping is needed, and what happens to the building drains when the vent piping is not working.

Plumbing Vent Questions & Answers, FAQs

These questions & answers about plumbing vents were posted originally at PLUMBING VENT CODES, DEFINITIONS, TYPES - topic home.

Our sketch of a plumbing stack vent was provided courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ].

On 2020-11-25 by (mod) - what's the purpose of a vent I see outside my house?

Lisa

I really want to help but I'm sorry to say I can't make out the situation from your text. You could try using the add image button to post a photo.

It's possible that you're discussing a crawl space vent that was blocked off. Venting crawl spaces usually doesn't work to keep the crawl space dry in the first place because the venting is too small and because seasonally we risk drawing moisture into the crawl space.

So current best building practice is to convert the crawl space to a conditioned space area, which means that it is kept dry and has a little bit of heat.

All of that is theory, because I can't see your building.

On 2020-11-25 1 by Lisa C

Prior to former owners “flipping” the 68 year old house where I currently live, laundry room was outside off of carport.

When remodeling to sell, owners had area enclosed between carport and laundry room and added stairs that lead to kitchen. Washer drains into pipe located in wall behind washer. Pipe goes into crawl space and water is removed via sump pump (I think).

There’s a vent to the outside of house on opposite wall of washer (near ceiling) that has been filled with insulation and closed off with plastic and duct tape.

What is this vent for and should it be closed off in laundry room?? Thanks!

On 2020-10-14 by (mod) - air coming up from a floor drain when it's being flushed out with a hose?

Lanette

That sounds pretty odd to me; perhaps the drain is partly blocked. If you are running water into the floor drain faster that it can drain out you may push air that was in the drain back up around the drain opening

On 2020-10-14 by Lanette

should there be air coming up from a floor drain when it's being flushed out with a hose?

On 2020-09-24 - by (mod) -

That's not normally necessary

On 2020-09-24 by Mike

Does vent line on roof get a screen?

On 2020-08-27 by Sharon

HELP!!! My carpenter pulled the main vent pipe that ran through the roof during a remodel in the bathroom!! I was putting in a larger shower, and the vent pipe ran through the wall beside old shower.

The wall had to be removed , and a new wall built 2 feet over, to accommodate larger shower. He tore it all out because it was in the way. I am a widow, did not have a clue what a vent was, or what it did!! When I called the plumber, he said there was a problem, saying if he had cut it off at the ceiling, they might have been able to tap into it.He installed an AAV, and said because it was such a short distance to main sewer line, it might be ok

I am so worried that I spent all this money on a remodel, and my house will smell like sewer and have drainage problems all through the house. Should I just wait to see if it works, or open the ceiling back up to see if they can connect?

On 2020-07-31 by Janet

Our builder didn't install the plumbing roof vents and will do so now after our tenants have been in the house for a year. Could there be any damage that I could check on?

On 2020-03-05 by Dean

020-03-05 04:22:53.940037 by Dean

Dean said:

These vent are servicing a toilet and a tub that have drains that are 2 feet apart. The vents will tap of within 2 feet of each other on separate branches and go up a stud bay 2 feet away. Ideally I'd combine into a 2 inch vent before going up the stud bay. Can I do that? Can I then introduce another 1.5 vent on the 2nd floor and the 2 inch continues to the attic?

Moderator reply

Dean:

What you want to do sounds right but I am always nervous about saying "OK" because of the high probability that there are more considerations that I can't see and you haven't noted. Just be sure to check the vent adequacy in diameter and distances and be sure to review PLUMBING DRAIN FIXTURE UNITS DFUs https://inspectapedia.com/plumbing/Drain_Fixture_Units_DFUs.php

On 2020-03-05 by Anonymous

Anon

Otherwise the vent may not work properly and could be subject to flooding.

On 2020-03-05 04:50:51.280388 by Anonymous

@Anonymous,
So what is the deal with needing to be above the basin line? I've heard this a few times. Thanks.

On 2020-03-05 by (mod) - combine plumbing vents?

Dean:

What you want to do sounds right but I am always nervous about saying "OK" because of the high probability that there are more considerations that I can't see and you haven't noted. Just be sure to check the vent adequacy in diameter and distances and be sure to review

PLUMBING DRAIN FIXTURE UNITS DFUs

On 2020-03-05 y Anonymous

Anon

Otherwise the vent may not work properly and could be subject to flooding.

On 2020-03-05 04:50:51.280388 by Anonymous

So what is the deal with needing to be above the basin line? I've heard this a few times. Thanks.

On 2020-03-05 by Dean

These vent are servicing a toilet and a tub that have drains that are 2 feet apart. The vents will tap of within 2 feet of each other on separate branches and go up a stud bay 2 feet away. Ideally I'd combine into a 2 inch vent before going up the stud bay. Can I do that? Can I then introduce another 1.5 vent on the 2nd floor and the 2 inch continues to the attic?

On 2020-03-04 by mod - want to combine plumbing vents

Dean you can combine vent piping provided you respect the horizontal distance limitations.

On 2020-03-04 by Dean

Can I combine 2 vents into a larger vent to go up and connect into the main vent? I have been told that each vent must remain separate until it is above the highest basin in the house.

I have 2 1.5 inch vents starting in the crawlspace, one for a toilet, one for a tub, that would be easier to combine into a 2 inch to go up to the 2nd floor and join into the rest of the vents for the house in the attic, which then exit the roof in one 4 inch. Ideally I would also pick up a 3rd 1.5 inch vent on the way as well on the 2nd floor, but not required to.

As it is, I would need to keep all 3 1.5 inch vents separate until above the 2nd floor sinks.

On 2020-01-06 2 - by (mod) - A clog in a plumbing vent system will affect all fixtures that are downstream

Mary

A clog in a plumbing vent system will affect all fixtures that are downstream from that point.

However I speculate that not all fixtures will be affected to the same extent. It's likely that fixtures closest to the clog will suffer the most.

Try clearing the toilet drain first.

On 2020-01-06 0 by Mary

I have a duplex if a vent pipe gets clogged would it affect both toilets and all drains. Cause one toilets plugged with no other draining issues. Tenent thinks the vents plugged can that be

On 2019-12-10 - by (mod) -

Tom

No, it's important that your plumbing vents are vented to the building exterior. What you don't want is any possibility of venting sewer gases inside the building.

The risk is both a sanitation issue and that of a possible methane explosion. However it might be possible to run your vent lines horizontally out through a Gable end wall and then up above the roofline.

On 2019-12-10 by Tom

I have a metal roof. Can i use a vacuum breaker on my vent stacks in the attic

On 2019-11-21 - by (mod) -

Smog

It may be possible but what you feel left out and need to consider is the total distances involved and the piping diameters.

On 2019-11-21 by Smog

Dear Sir.madam I have a row of toilet vents terminated at the roof slab. Is it permissible to join the
whole row with a horizontal vent pipe then ventilate at the far end.

We do not have snow in Nairobi therefore do I still need to raise the vent
90cm above the slab?

On 2019-10-11 by (mod) -

Carlton

It sounds like a rather basic plumbing job. Depending on the piping material that's used it maybe a simple is gluing an extension into a union that mates with existing vent.

Just keep in mind if you make your extension too high you may find damage to the piping from wind or snow load

On 2019-10-11 by (mod) - shower drain gurgles after toilet is flushed.

If this is a recent problem I would start by checking for a drain that's blocked. You may need help from a plumber to clear that line.

If the shower drain has gurgled when the toilet is flushed - since original construction of the home then it's possible that the drain is not properly vented

On 2019-10-11 by giovanni

shower drain gurgles after toilet is flushed. how to fix the issue, all plumbing has been installed and walls are closed.
thank you

On 2019-10-11 by Carlton

My house has 2 vents(1 is 3 1/2 ID & 1 is 4 1/2 ID) that extend a ft . to 1 1/2 ft. above roof and sometimes get covered by snow and I would like to extend them. They have an outer sleeve that has about an inch air space. The house was built in the 1960's. where could I get extensions and how much could I add? Thank you

On 2019-09-04 by (mod) - flipping a home with no proper plumbing vents?

PRetty odd to have NO vents through the roof.

Watch out: I'd look for trouble such as someone having left a vent dumping into an attic.

On 2019-09-04 by Jim

I purchased a flipped home. I don’t have a vent pipe on my roof, there is a sure vent on my kitchen sink according to the town inspector if there is a sure valve then it is to code but I thought a vent pipe is still needed to lead gases to the outside?

On 2019-05-30 by (mod) -

I'm not sure what exactly the conditions are in your building. If you're describing for example a floor drain and you seal it off, you avoid it back up in that location but of course it means that any water spilled on the floor does not drain.

On the other hand if you're describing a sink or tub drain then blocking off next to fix your unusable. In any case all that you're doing is treating the symptom not the problem.
Sounds to me as if the problem is a partly blocked Plumbing drain or inadequate venting.

The risk of those ranges from inconvenience and noise to sewer gas contamination or even explosion in a building to a sewage backup in a building.

So considering that the worst cases could be serious it would be appropriate to get some help from a plumber.

On 2019-05-30 by Sabrina

Hello I have a drain or vent on my floor that when the shower is running and someone use the toilet at the same time or just the shower is running, there is water coming out of this floor drain or vent. 1st. Can I remove or close this drain/vent without creating another problem? Or can this be fix so water will not come out of it?

On 2018-12-04 by Doug

How many pluming fixtures can be vented by a single 2" vent stack through the ceiling?

On 2018-10-25 by (mod) -

There could be something subtle that I don't understand, but on the face of it having more vent capacity should not cause a problem with drains. Rather its usually the opposite.

On 2018-10-25 by Tk

Will having 2 vents on one drain cause problems they ate very close to each other

Question: can the soil stack curve above ground to avoid a wall?

I am trying to find out if the soil stack can be curved above ground because there is a wall that I need to move. The wall will moved about 1 1/2 feet and the soil stack is currently inside the wall that I desire to move. This is in Portland, Oregon. The pipe that was used for the soil stack is cast iron, but I want to change this to the black ABS. Are there restrictions to how much the pipe can be curved? - Enan

Reply:

Take a look at the UPC (see citations in the article above or at "References" below. Certainly I've seen plenty of soil stacks (vent piping) that were not straight runs in above-ground (or above building) routing.

Because the above building vent pipe is venting sewer line gases and moisture, not liquids or solids, flow restrictions seem less likely a concern.

You might however want to look at the total above-ground run length vis-a-vis the vent pipe diameter because in a freezing climate a very long above-ground (above roof) length might increase the risk of freezing condensate and thus vent blockage in winter weather. In buildings I've examined I've not seen blockage in larger diameter vents at or above 2" but I've certainly seen it in smaller pipes.

Follow-Up comment:

Actually the part of the pipe that I wanted to curve would be down in the basement below the water closet (toilet, sink, and shower)There is only 1 restroom in this house. This means that the part that is curved would be under load from all the water draining from the sink, toilet, and shower. I was trying to avoid tearing up the concrete floor to install new drainage pipe and also because of how close the soil stack is to the cement wall in the basement.

The basement is not a full basement, but about a quarter of it is still crawl space which has been framed, and drywall installed (its used for storage). The soil stack runs next to this wall that is half concrete half drywall.

My plan was to cut the soil stack about three or four feet above the concrete floor and then do a 45 degree turn until the pipe enters the drywall portion of the partitioned wall and then have it go straight up to the roof.

Do you know if that might cause a problem with the pipe being under load from the drainage of the water closet? I planned to change everything above the cut that I make into the cast iron pipe with ABS. Of course I would brace everything that needs to be braced.
Thanks.

Question: Can a sink and toilet share the same waste line and vent?

Can a sink and toilet share the same waste line and vent? - Jim

Reply: Yes but ...

Jim: yes vent piping can be shared, but all fixtures need to meet the distance requirements.

Question: drain trouble in a new house - bubbling lower floor toilet and slow drain

I just moved and seem to be having trouble with the drained in the new house. When someone is in the shower upstairs air bubbles come from the toilet downstairs. If you try to flush the downstairs toilet the water will not drain. Just wondering if anyone knows what the problem might be and what I can do about it. Thank you. - Lucas

Reply:

Lucas:

You may have a clogged building drain. Often a slow or partly blocked main drain line (or blocked septic system if you're not on sewer) can show up as bubbling and gurgling noises at fixtures lower in the building. Watch out for a sewage backup.

Question: one sink drains slowly and doesn't seem to clear - could it be a vent problem?

All the sink and toilets drain great in the house but one sink in the upstairs bed room. I have ran a snake, many times pipes are clean. Drain will handle water slowly. But if I fill the sink open the plunger or even take it out, it take an extremely amount of time to drain Could it be the dry vent if so, How Do I Clean it Thank you for you time. - Larry Miller

Reply:

Larry,

Indeed there could be a venting problem that leads to slow drainage but usually if that is the case for a given bathroom, in that bath, since usually all fixtures share a common vent, you'd expect to hear a glub glub sound when the drain is flowing, and flushing the toilet might produce noises at the sink drain. Maybe.

Depending on the lengths of drain, your snake may not have reached the blockage. Also sometimes a small diameter drain snake will pass right by a blockage but not make a sufficient opening to clear the drain.

If the drain used to work but has become worse, I suspect a crud/hair/soap scum blockage or if the house is old, and if drain piping is iron, perhaps rust clogging. I once paid an absurd sum to Plass the Plumber to "run a wire through a clogged drain" - a step that the plumber completed, got paid-for, and left.

But his work did not help open the drain one iota. Later we began tearing open the wall to remove and replace galvanized iron drain piping. When I removed a short horizontal drain section in the wall between the sink and the main drain line, it was apparent that that section of piping was nearly 100% blocked by rust and iron deposits. The "wire snake" had just passed through that little opening but had not helped a bit. Really the only fix for that condition was to replace the piping. There was too much solid deposit to clear with a snake or with drain cleaner.

A more obscure vent problem that might leave the other fixtures draining OK could be found in a large bathroom at which the sink drain included its own vent pipe loop that eventually finds the main vent stack - and an odd coincidence of an insect or rodent blockage in just that vent - but frankly that's pretty unusual.

In sum I think you may want to pull the sink trap and try snaking with a rotary drain cleaner for a distance that leaves you sure that you've reached the main drain into which the other bathroom fixtures flow.

Follow-Up Comment: Derek Plumber offers more advice on clearing a blocked drain

A snake does not always completely clear a clog, blockage depending on how long it has taken to build up the blog, blockage can mean a difference in how you approach. Of course start with a snake the issue u have with it still draining slow is most likely that as you have gone through the clog, blockage and pulled the snake out that the Black Tar is just collapsing back on itself thus making it nearly impossible to clear with a snake.

If you have it draining slow this means that you have only cleared a path through the clog, blockage and that the issue is still there and will eventually blog up again.

You can try running your HOT water slowly while using your snake in a back and for motion many times over attempting to pushing what breaks free and is small enough for the water to push through ... a plunger will have little effect in forcing this down the drain.

This may or may not work.

Your best approach at this point, now that it will drain is to use a power flusher (you may be able to rent one)the hose is sized for the drainage pipe your working with, this works by spraying high pressure water usually min 1500 psi through the hose which has a variety of different heads attached to end. Id suggest using the head that has 3 holes spraying backward as it will help u by pushing itself through the pipe.

Make sure the hose is a good 3 feet in the pipe and u have a firm grip on it where it enters the clean out turn it on and run it slowly down back and start over till it is good and clear. - Derek Plumber

Question: how to move a toilet across the room - drain vent pipe distance trouble

I am trying to move a toilet 8 feet across a room, meaning that my venting pipe will be farther away than 5 feet. If I use the same soil stack, sloping the drain pipe 2 inches down over the 8 feet, do I need to add another vent stack pipe closer to the toilet to allow for air to escape,

or can I allow the toilet to vent off of the existing vent stack? If I need to tap another vent stack into the line, any recommendations on how that needs to work?
Thanks! - Steve Strong

Reply:

Steve, if the toilet waste line is 4" or more ID, one of the sketches above, as I read it, says you can go up to 10 feet away from the soil stack. Make sure you have proper slope as well.

Question:

Can I have 3 toilets on 3 different floors connected to the same vertical 3 inch soil pipe without separate vent pipes also added? Other wet vented fixtures are connected upstream from the toilet on the 2nd floor, which is the highest floor. - Larry Gatti

Reply:

Larry, yes; you will need to review DWV layout schematics in the model codes or training manual.

Question: definitions of discharge stack, waste stack, vent pipe

what is differentiate between discharge stack,waste stack and vent pipe. - Yana

Reply:

I take those terms to all refer to the vent pipe

Question: can water in the basement come from a leaky vent stack drain line?

When I have a heavy rain I have a puddle in the basement next to the bathroom drain pipes. This only happens during a heavy rain storm. Could I have a leak around the bathroom vent pipe? - Ray

Reply: yes but ... check these two other wet basement diagnosis clues

Ray, I have seen a few cases in which leaky vent stack flashing at the roof allowed water to run down the outside of a vertical plumbing vent stack pipe that in turn was enclosed in a chase-way that ran from roof to basement - water might indeed then show up in the basement.

But there are at least two other things to check:

1. Look for leaks into your sewer piping or backups that occur in flooding or very wet conditions.
2. Try inspecting your basement several times, with great care and a good flashlight during heavy rains. I have found that water can leak into a basement at a wall - say near a corner downspout that is not routed away or from roof gutters spilling over - then run across the basement floor to a low spot where water forms a puddle, leaving very little water along the path between the actual leak point and the puddle. If much time passes between the occurrence of the leak and the inspection, we may see only the puddle, and not the water track that leads back to its true source.

At BASEMENT LEAKS, INSPECT FOR we provide a series of inspection points useful for sure diagnosis of the cause of wet basement floors.

Question: how much clearance between plumbing vent discharge opening and top of brick chimney?

How much height clearance do I need between my plumbing vent discharge opening and the top of my brick chimney? Our vent pipe is located about 15 inches from the chimney. Chimney and vent are near the ridge (peak) of the roof. - Tim L.

Reply: Two feet or 24" is a code interpretation for distance between plumbing vent stack rooftop termination and the top of a chimney that is less than 3 ft. away.

Tim L - thank you for your question. I've reviewed and edited our section above on plumbing vent clearances to give code citations and details. I don't find chimneys explicitly named in plumbing vent sections of the model codes, but the distance to the "Nearest window, door, opening, air intake, or ventilation shaft" distance to plumbing vent needs to be 10 ft. horizontally OR the vent should terminate at least 24" (two feet) above the opening. I take this to include chimneys.

Question: do these plumbing vent specification codes apply in Canada?

(Nov 28, 2011) SteveStrong said:

Thanks Dan. I have spent a few hours reading through building codes today to make sure that I can get away with it as well, but to no avail. You don't happen to know if this standard would be accepted in Ontario, Canada, do you?

Reply:

Steve Canadian plumbing codes are similar to but not identical to the U.S. versions. What does your local building department say?

By the way, the illustrations in most of the plumbing vent article were contributed by Carson Dunlop Associates, a Toronto, Canada engineering and home inspection firm.

Question:

(Jan 18, 2012) william tingson said:

can i used 4 in. diameter soil stack as wet vent piping for a 16 story building serving total of 16 toilets attached to it?

Question: how much clearance between plumbing vent discharge and chimney top

(Apr 7, 2012) Tim L said:

How much height clearance do I need between my plumbing vent discharge opening and the top of my brick chimney? Our vent pipe is located about 15 inches from the chimney. Chimney and vent are near the ridge (peak) of the roof.

Reply:

Tim L - thank you for your question. I've reviewed and edited our section above on plumbing vent clearances to give code citations and details. I don't find chimneys explicitly named in plumbing vent sections of the model codes, but the distance to the "Nearest window, door, opening, air intake, or ventilation shaft" distance to plumbing vent needs to be 10 ft. horizontally OR the vent should terminate at least 24" (two feet) above the opening. I take this to include chimneys.

Two feet or 24" is a code interpretation for distance between plumbing vent stack rooftop termination and the top of a chimney that is less than 3 ft. away.

Tim L - thank you for your question. I've reviewed and edited our section above on plumbing vent clearances to give code citations and details. I don't find chimneys explicitly named in plumbing vent sections of the model codes, but the distance to the "Nearest window, door, opening, air intake, or ventilation shaft" distance to plumbing vent needs to be 10 ft. horizontally OR the vent should terminate at least 24" (two feet) above the opening. I take this to include chimneys.

Question:

(Apr 9, 2012) milo said:

The remodeling crew moved the vent pipe which terminated on the roof to terminate on the dorm side. (This is a cape cod style house with a dorm on the most upper floor.) There is no window or other ventilation (except fan vent) opening nearby. They want to terminate the vent pipe with an elbow facing downwards. Does this installation make a sense?

(Apr 11, 2012) Danny said:

I am installing solar panels on my roof. I need to move a plumbing vent stack. Right now, the stack is closer to one side of the run in the attic rather than in the middle. On the short side, I have a bathroom sink, Jacuzzi, shower, toilet & kitchen sink. On the other side of the run (long side) is a bathroom sink & toilet. My only 2 choices are 1) move the stack about 6 feet closer to the short side & then higher on the roof next to an attic fan or 2) about 20ft closer to the end of the run. Is either option better? Thanks

(Apr 12, 2012) Ibrahim said:

A comode was connected to vertical soil pipe through a pipe of 4 in diameter and about 8 ft length. A vent pipe of 2 in diameter was connected at the middle. A sink was connected to the 4 in horizontal soil pipe after the vent pipe near to the vertical soil pipe. Another 2 in waste line was connected to the 4 in soil pipe. But whether it was not clear whether this 2 in waste pipe connected before the vent pipe or after. Now there is odor in the toilet. All toilets in that vertical line of a 14 storied building suffer from this odor problem. can anyone suggests what can we do?

Question: is it ok to use a vacuum breaker plumbing vent - mine smells?

(May 23, 2012) Lorie said:

We just rented a 1920's bungalow in a great part of town. As I have been unpacking and cleaning I have noticed a whiff of sewer smell every so often. I started looking around, and found that under one of the sinks, there is a round thing that has "VENT" on it. It is connected to the rest of the pipes under there. I am no plumber...but, isn't this supposed to be outside? And what do I tell my landlord? Thanks!

(May 23, 2012) Becky said:

We too have the "under sink" pipe with holes that vents. We have one bathroom that gets sewer smells. Someone told us to cover those vent holes under the sink to eliminate the sewer smells. Is that a good idea

Reply:

Becky and
Lorie:

You are perhaps describing a vacuum breaker "vent" that is substituted to improve drainage when there is no in-wall actual plumbing vent pipe. The vacuum breaker allows air INTO the plumbing drain as water goes down the drain (preserving the water in the trap against siphonage and sewer gas smells) but it is designed not to let water out.

Becky don't close off a vacuum vent or your drains won't work properly; but if there are smells you need to find and fix the problem - a vacuum breaker vent that doesn't work and needs replacement, or a home-made and unsanitary substitute - send us some sharp photos and we can comment further.

Beckyt, take a look at SEWER GAS ODORS for more information.

Question:

(June 20, 2012) Anonymous said:

In the basement I have 2 wash machines & 1 laundry tub connected to a drain that is vented. The vent was outlet pipe is located on the outside wall at approx 8 feet with a 90 degree elbow facing down. Is this way of plumbing ok fot the 1st floor of this house. Also if its ok I would like to connect another washer and laundry tub on the second floor to this drain line and vent.

I am not sure if I can connect to thgis vent located below the new 2nd floor plumbing. I can also extend a pipe up to the ceiling and cross over in the attic and connect to another exsiting vent, if I did that there would be drain lines fromm the downstairs 2 washers, 1 laundry tub and upstairs washer drain and one tub having 2 vents one vertical between floors and one in the roof plus. Is that ok.

Reply:

Anon the question is a little unclear to me, but it's not uncommon for a plumber who is adding a retofit plumbing vent where one was missing to run the vent outside the building and up under the eaves (away from windows). There are some plumbing designs (wet venting) that allow a vertical DWV pipe to function as both drain and vent, but I suspect yours is too small in diameter; and I don't like running drains outside and down the wall especially in a freezing climate.

Question: connecting a sink to an existing vent stack

(July 20, 2012) Doug B said:

I'm moving a sink and it is within 5 feet of a vent stack but I cannot connect directly across to it.
From the sink I would like to drop down into the crawl, then combo the vent line off horizontally (sloped up) to the stack, whilst the drain drops a little more and then slopes to join the main 3" line.
Would this work or do I also need a loop vent from where the waste 90's down to go up passed the flood level then loop down to the horizontal vent line?
Cheers.
(attempt at diagram)

sink vent
| |
----- |
| |
| |
| |
---------------
|
|
____________
|
join waste line

Reply:

Doug, take a look at the "wet vent" description in the article above -- that's about as close as we can get to your design.

Question:

(July 24, 2012) Morgan said:

What's the UPC's max distance from flange to vent for a wall mounted toilet?

Reply:

Fair question, Morgan; I hadn't considered if a wall-mounted or backflush toilet would have any reason to have different distances to the plumbing vent than a floor mounted toilet. While I'm doubtful, I'll research further - but am traveling so don't have UPC at hand. Perhaps another reader with her own copy of the Uniform Plumbing Code can help us out.

Generally I'd assume the distance requirements are the same as for a floor mount toilet.

Question: distance from window to vent stack outlet

(Aug 26, 2012) Colin said:

how far from a window can you fit a outlet to a vent pipe for a soil stack

Reply:

See VENT DISTANCES to BUILDING FEATURES

Question:

(Aug 27, 2012) Ron Schwarz said:

I would like to ask a question. If a toilet line is the only item on a 3" waste pipe and is over 6 feet in length so it needs a vent it, can you put in a horizontal vent line for about 5 ft before it goes vertical to a horizontal vent line that runs to a stack about 3 ft away? Should that vent be put in ahead or behind the toilet location, ie, should the toilet be at the end of the waste line?

The toilet is the only item on that waste line.

Question:

(Sept 14, 2012) Guy said:

I've had a toilet that has been a problem since I bought this home. I have taken the toilet out, and all is clear inside. I've also inspected the pipe, and it's all clear too. The vent is also clear. I had sort of come to the decision that I have to replace the toilet. It generally flushes ok. The flush starts out good, but often never finishes well. I have two of these exactly the same, and the other one is fine. I noticed on the one that is fine, that at the end of the flush, there is a glup or two of air at the end. The one that gives me grief rarely does that.

Today I happened to take notice of how this toilet is plumbed. The base flange goes directly into a 4x4x1½ T. The 1½ off the T continues over to another T . That goes to the sink right beside the toilet, and then continues up to the roof for venting. I never have any problems with the sink, nor are the toilet flushes pulling air from the sink. Is my problem possibly related to the fact that the vent is ring in that T where the base flange from the toilet goes into?

Reply:

Guy,

Before replacing the toilet, consider that that step may not fix the problem - especially since you report that the same model toilet works fine elsewhere in the home.

That suggests there is a problem with the vent system design or condition (lacking adequate venting) OR a clog you haven't found, OR a toilet with a hidden obstruction, OR (commonly) the toilet fill valve and fill level are not working properly. Be sure the water volume is up to the fill line marked in the toilet tank and that the flush valve operates properly. Once that's ok, I'd check into the vent system since that's what is suggested as the most likely problem from your own notes.

Question:

(Sept 17, 2012) Heather said:

I am having to relocate the basement bathroom to the other side of the basement from the main soil stack. If we used a sump pump to transport the waste back to the mail soil stack, could the 1/4" per foot slope be avoided?

(Oct 18, 2012) Linda said:

Can a toilet be vented in to a loft space or should it be vented in to the atmosphere? Also can a toilet vent go around a 90 degree bend. Thank you. Lindai

Question:

(Oct 22, 2012) Kristine Groft said:

We have had a new bathroom installed( shower, sink and toilet) and has a terrible septic/gas smell... the plumber came back and stated they forgot to add a vent cap to the shower plumbing and so they added it along with a hole in the wall on the otherside of wall to vent into our closet... the smell is still there... shouldn't this vent to the outside?

Reply:

Russ D. said:

Kristine~
Your bathroom should have been vented outside (think straight up through the roof). Your plumber cheated.

Question:

(Oct 22, 2012) Lance said:

Is it acceptable to have 2 90° sweep joints near the bottom of my main stack before it goes into the basement floor? The old stack was set up in this fashion, but it was clogged something fierce. The house had been vacant for some time so I don't really know what exactly to attribute that kind of clogging to (there was 4' of stack filled solid with waste down to the floor joint).

The joints were necessary to get from inside the wall chase into the basement, where the wall extended several more inches to the inside of the home than the above floors did.

Question:

(Nov 10, 2012) Rich said:

It appears I have 2 bathrooms venting off of one PVC stack. Each bathroom contains a WC, shower and 2 sinks in one and one sink in another. The far bathroom has a odor we can not get rid of. First is this to code and second is there a PVC booster fan that can be installed to help lift the air in the dry stack?

Reply:

Rich

To code ... Depends on distances, slope, and similar details. Have you looked at the plumbing odor diagnosis article at inspectapedia ?

Question:

(Nov 21, 2012) Lucie said:

No one I've spoken to--carpenters, plumbers, contractors--has seen the horizontal venting our plumbers installed for our new bathroom. How common is horizontal venting, & are there any specific regulations for it? It already doesn't follow the specifications you listed above--less than 2 feet from a chimney & not above the window (about 5 feet away). So do you know anything about this?

Reply:

Lucie,

It sounds ad if you need help onsite from your local plumbing inspector

Question:

(Nov 28, 2012) Scott said:

I just moved into my new house and it seems that ALL (3 1/2) bathrooms CLOG so easily.. Like I never seen before. This was never the case anywhere else I have lived. It's not just me, It's my entire family! What could be the problem that is causing ALL toilets to clog easily?

(Dec 20, 2012) richard wilson said:

I am having with the toilet in 1 of 2 bathrooms, that will not flush completley just a slow drain. I removed toilet and snake for blockage, when I installed toilet it it worked fine twice then back to the same thing. Can the vent sys. be a problem?

Reply:

Richard, a blocked plumbing vent can certainly cause toilet flushing problems, but so can a partial drain blockage and even a toilet tank or bowl that are not filled to the proper level. Check the toile tank and bowl fill levels first.

If the toilet flush kind of goes glub glub glub or burbles during flushing that's usually a partial drain blockage;

If when flushing the toilet you see or hear glubbing at a sink drain the problem could also be a missing or blocked plumbing vent.

If all fixture drains are slow that often means a blocked main drain.

Search InspectAPedia for "Slow Toilet Flush" or "toilet repairs" for details.

Question:

(Dec 24, 2012) aaron said:

i have a vent stack that is 8 ft away from the toilet but need to move it another 6 ft more to hide it in the wall so i can put in a bath tub. will it still work for the toilet at that distance and with a bath tub drain before the toilet ?

Reply

(Jan 13, 2013) Richard T said:

Can I run a sink waste water outlet direct into a vent stack?

Reply:

If it's a wet vent desigbn

Question:

(Jan 13, 2013) RICO said:

WHAT IS THE CODE REGARDING THE VERTICAL DISTANCE OF PIPE FROM GRADE BEAM? THANKS

Reply:

x

Question:

(Feb 5, 2013) Anthony C. said:

I have 2 very small full bathrooms, 1st & 2nd floor in line with each other. I want to hollow out the wall directly behind & above each sink and toilet to countersink shelving and/or cabinetry to save space. Are these typical locations for pvc vent pipes? My house was built in 1988. Thank you

Question:

(Feb 9, 2013) Ryan N said:

I am having a double storey extension and a garage on the side of that built, i am moving 2x soil stacks into the garage (which has a pitched roof away to the side).
do i have to run the stacks through the garage roof and all the way up the outside wall to the top of the main roof or can they terminate just above the garage roof for venting? there is no windows on that side of the house.

Reply:

Ryan, you can vent out through the garage roof but must meet the clearances from upper floor walls, windows, etc. Found in tables in the article above.

Question:

(Mar 1, 2013) LEN said:

I want to remove a small wet bar sink and enlarge the space to put in a pantry. Will it be ok to cap off the vent pipe where the vertical pipe meets? And just drywall around it.

Reply:

Len,

Sure, it's fine to cap off an unused drain as you describe. You are not interfering with the vent itself.

Just be sure the cap is properly sealed lest later your remodel doesn't suffer a sewer gas leak.

Question:

(Mar 8, 2013) Ron said:

I am adding a half bath in the basement of a two story house. The 3" drain coming from the first floor runs horizontally along the floor joists for a distance of about 15 feet before turning back vertically to go through the basement floor. I am adding the toilet within 3 feet of the vertical pipe. Can I still use the vertical 3" drain as a vent for the toilet and sink?

Reply:

Ron, I don't have a totally clear picture, but probably we can say yes, so Lon as the vent is just a dry vent.

Question:

(Mar 12, 2013) GAry said:

In a commercial building I want to add floor drains in the middle of the floor for cleaning. This will be the start of the sewer line and attatch into an existing line. I cannot get a vent line to the first 3 floor drains for a distance of approx 30 to 40 ft. can these 3 floor drains be wet vented until I tie into the existing line?

Reply:

Gary,

You are right to be concerned as a floor drain can send backing up sewage into the room. You will want to

- make sure the floor slopes to the drain
- install a check valve type floor drain trap that will let water ( or as needs, air) into the floor drain, but guards against sewage ban cup.

Question:

(Mar 23, 2013) Andrew H said:

If I run my 3" toilet drain into the sewage basin 5 feet away, do I need a serperate vent for the toilet (the sewage pump/basin will be vented)?

Reply:

Andrew H

You are within the distances cited in the vent distance tables above.

Question:

do the sweet air charcoal plumbing vent filters used to eliminate odors comply with the uniform plumbing code?

Reply:

Walt: I don't know of a plumbing code regulating plumbing vent filters, but if such a device obstructs vent flow it would be improper as it may interfere with proper drainage; further, such devices should not be required in a correct installation; it's treating the symptom not the problem.

Question:

(Mar 24, 2014) Jud said:

Our single story house has a hip roof and the 3 in cast iron bathroom stack vent pipe runs from the drain pipe under the floor up through a chaseway up through the attic. Last year, we noticed damage to the chase drywall outer layer extending from the floor up about 2 feet. The visible damage was paint bubbling and pulling away from the wall in small pieces and a rustlike colleration of the exposed drywall surface. We sanded, patched, primed and painted the area.

The problem is now showing up again nearest the floor. No sign of leakage in the attic but when looking up from the crawl-space you can see the subfloor wood around the pipe is wet and actually sheds occasional drops of water when the fixtures aren't in use. We suspect condensation on the pipe in the chaseway that is dripping on to the surrounding floor wood, which is moist and punky. Any suggestions on the cause and our solution options?

Reply:

Jud, it seems plausible from your note that there is condensate on the vent pipe that drips into the chaseway, but I would not rule out the chance that condensate from inside the vent could also leak out if that piping were imperfectly installed.

Condensate on the vent exterior: if warm moist building air enters a chaseway where a vent pipe is chilly its outer surface will collect condensation.

Condensate from vent interior: moisture regularly moves up inside vent pipes to the rooftop exit; taking a long hot shower can send enough moisture into a vent stack to accumulate as frost. If the vent piping is not water tight, when the frost or ice melts it may leak back out into the building.

Rooftop leaks into the vent chase can occur if the vent flashing is not correctly installed.

All 3 of these merit consideration.

I think to get to the bottom of this we need a clear look through the chaseway following the vent piping until we see where moisture or condensate is forming or leaking out. Watch out also for mold formation on hidden surfaces of the chase, walls, floor etc.

Question:

4/5/2014 Phil said:

Does a kitchen sink with a double bowl need a vent. Out builder says it does not. I don't like this.

Reply:

Phil

There's "need" and then there's "need"

- with a double sink you don't need a vent for the drains to drain - in that while sink A is dry and Sink B is draining it will draw air in through the trap or drain line for A.

- but you absolutely need a plumbing vent serving every plumbing fixture, including double-sinks, not only to comply with code but for proper, effective drainage (say when both sinks are filled), and to avoid back-drafting of sewer gases due to loss of water in the sink trap.

About your builder, I'd keep away from him. If you are building new construction or working under a permit that requires a plumbing inspection, and if your municipality employs someone who's actually awake and actually goes to the job, in my OPINION s/he ought to be concerned about a kitchen sink with no vent.

Solutions accepted in *some* municipalities where there is no vent to the outdoors above the roof line, is a vacuum-breaker "V-200" type vent right under the sink.

Question: is a plumbing vent needed on a double-bowl kitchen sink?

(Apr 6, 2014) Phil said:

Does a kitchen sink with a double bowl need a vent. Out builder says it does not. I don't like this.

Reply: Yes

Phil

There's "need" and then there's "need"

- with a double sink you don't need a vent for the drains to drain - in that while sink A is dry and Sink B is draining it will draw air in through the trap or drain line for A.

- but you absolutely need a plumbing vent serving every plumbing fixture, including double-sinks, not only to comply with code but for proper, effective drainage (say when both sinks are filled), and to avoid back-drafting of sewer gases due to loss of water in the sink trap.

About your builder, I'd keep away from him. If you are building new construction or working under a permit that requires a plumbing inspection, and if your municipality employs someone who's actually awake and actually goes to the job, in my OPINION s/he ought to be concerned about a kitchen sink with no vent.

Solutions accepted in *some* municipalities where there is no vent to the outdoors above the roof line, is a vacuum-breaker "V-200" type vent right under the sink.

Question: Ok to dump plumbing vent indoors?

9/12/14 Jim said:

We had a new roof installed and they never extended the vent pipes through it, is this a health issue?

Reply: no, not OK

Jim

possibly, ultimately, as you are dumping moisture into a roof cavity, and worse, potentially dangerous (like blow up the house?) as you may also be venting explosive methane-containing sewer gas into the building. Check with your local building department.

Reader Comments / Kudos / Gripes

(Apr 23, 2011) D bushnell said: very informative for someone not familiar with drains but the dimentions in the illustrations are not readable even on my hi def laptop.

Reply: RE: Reading detailed plumbing dimensions in our illustrations

Please just click on any image found at our website to see an enlarged, detailed version that is quite legible.

We apologize that on some of our small on-page images the text is tiny - that decision was made to make pages load quickly.

Thanks for the critique - Editor

(Apr 27, 2011) Chris said: Thank you so much for this site! SO helpful!

(May 22, 2011) Dr. Beer said: Very nice explanation and diagrams. Thanks!!

(June 5, 2011) Anonymous said: Excellent. My city claimed I had a "wet vent" situation which wasn't made clear to me by the inspector. Fortunately I used this information to counter the claim. Home Owner Wins!

(July 19, 2011) IAN sloan said: Thank-you for the great information. I now have a basic understanding of Dry verus Wet Venting.

(July 29, 2011) brandel said: excellent explanations many thanks!

(Aug 27, 2011) Anonymous said: Very helpful information. I find it easy to follow and tells me just what I need to know. The text with the illustrations makes an effective lesson. Thank-you!

Question: health issue if plumbing vent spills into attic?

(Sept 14, 2011) Bob said:

In the sketch of the wet vented toilet drain, can a portion wet vent piping be horizontal?

(May 15, 2014) Tim said:

In a basement bath if the seweage pit (with 2 inch vent) be used as a common vent for the toilet (2 feet away) and the showere (4 ft away)

(Sept 10, 2014) Jim said:

We had a new roof installed and they never extended the vent pipes through it, is this a health issue?

Reply:

Jim

Watch out: ultimately, as you are dumping moisture into a roof cavity, and worse, potentially dangerous (like blow up the house?) as you may also be venting explosive methane-containing sewer gas into the building. Check with your local building department.

Question: sink 25 feet from an existing vent?

(Sept 17, 2014) Nick Devora @ esterline.com said:

I have added a "Y" fitting onto an existing building cleanout so that I can install a sink @ 25' away, my 2 questions are

1) Do I need a vent or will a pee trap work?

2)Since I do not have the sink installed can I just cap the line temporarily?

Reply:

25 feet is too far from an existing vent - you'll need one for the new fixture; possibly your local code inspector would approve a "cheater vent" or V-200 vacuum breaker vent at the trap instead.

Question: vent through wall or through roof?

(Sept 26, 2014) Frankie said:

I'm looking at buying a house and while inspecting noticed what appears to be the vent of the fixtures of a bathroom installed in the exterior wall. At first glance it appears to be located far away from windows and doors. Is this an accepted practice? If it is, where in the code is this referenced? I was under the impression that the plumbing code mandated that vents need to discharge at roof level.

Reply:

Frankie the local plumbing inspector can indeed approve a plumbing vent terminating through a building wall provided that clearance distances from windows or other air intake points are met.

Question: Can an experienced plumber direct sewer gas that builds up from a dry drain into a living space?

10 April 2015 Cynthia said:

I am curious whether one who is an experienced plumber can manually direct sewer gases through plumbing vents. In other words, can a plumber nefariously direct sewer gases into an apartment?

I have an unusual situation. Approximately 6 months ago our drain in the bathroom shower started to gurgle every time we flushed the toilet. The maintenance men examined the problem and told us that it was due to "dry drain" and that there was no clog. However, subsequent to their telling us this we started to get "fumes" in the apartment, beginning with a "rotten egg" smell and then a sort of "garbage" odor that affected both of us with watery eyes, difficulty breathing, headaches, irritability (panic set in) and muscle aches and pains. When we contacted the landlord they ignored us. We called and called but no response. This was unusual, for they always were prompt in responding.

Simultaneously to the gurgling in the shower, around the time it started, two new tenants moved in next door, one of whom worked for a plumbing and heating company, the same company I filed a police report about approximately 2 months before the new tenants moved in. I did so because a former large corporation ex-employer were in a legal battle at this time.

I was having computer problems as well - that I attributed to the presence of the truck outside my home that had a man sitting in it - with a light at the back of the van - until 2:00 - 3:00 am. Later, I looked at the company's website and became aware that not only does the company deal with plumbing and heating, but also sophisticated security systems, where it boasts of being able to make use of fiber optics in cable to remotely make a phone work - even in a storm.

I do not believe my new neighbors live in the apartment as their primary residence. That is because they are up all night, and it is ONLY at night in the wee hours of the morning that the fumes engulf the apartment.

Can an experienced plumber direct sewer gas that builds up from a dry drain into a living space?

Reply:

Cynthia if the plumbing traps are dry, sewer gases are likely to rise up the drain line and escape through the dry-trapped fixture into the building by natural convection; the wicked plumber doesn't have to do a thing to make that happen.

Watch out: sewer gases contain explosive methane.

 

 

...

Continue reading  at PLUMBING VENT CODES, DEFINITIONS, TYPES or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see PLUMBING VENT FAQs-2 - more recent questions & answers about plumbing vent piping, location, routing, size & distances

Or see these

Recommended Articles

• PLUMBING DRAIN NOISES where we explain the basics of proper plumbing vent piping and how errors cause trap siphonage, odors, and noises
• PLUMBING VENT DEFECTS & NOISES - home
• PLUMBING VENT CODES, DEFINITIONS, TYPES
• PLUMBING VENT REPAIR

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