Photograph of a loose, improperly installed, slanted plumbing vent above the building roofPlumbing Vent Definitions & Code FAQs
Q&A about plumbing vents & vent codes

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Plumbing vent and vent code questions and answers.

This article series defines plumbing vent system terms, distances, and functions, and other specifications and code requirements.

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Q&A on Plumbing Vent Terms, Definitions, & Types

Plumbing vent terminology sketch (C) Carson Dunlop Associates These questions and answers about plumbing vent codes and definitions were posted originally at PLUMBING VENT CODES & DEFINITIONS - home - be sure to check that ARTICLE INDEX and advice.

The basic plumbing vent terms are shown in the sketch at above/left. In these notes, the plumbing stack vents and other sketches included below are provided courtesy of Carson Dunlop Associates. [Click to enlarge any image]

On 2018-05-22 by (mod) - how come I smell the sewer first thing in the morning when I brush my teeth

I'd look for

- sulphur in the water supply first


- check for blocked or slow drains or a blocked vent pipe that is causing siphonage out of the sink trap

DIAGNOSTICS: before you brush your teeth lean down and sniff the sink trap / does it smell particularly bad?

Then when you first turn on water in the sink, lean down (don't bang your teeth into the faucet) and sniff the water stream - does it smell bad?

On 2018-05-21 by Anonymous

it hasn't always been like that maybe just the last couple of months

this is a 1969 mobile home unit. how come I smell the sewer first thing in the morning when I brush my teeth

On 2018-05-02 by (mod) -

See if your local inspector will approve
An air admittance valve

see AIR ADMITTANCE VALVES AAVs - Studor Vents Explained

On 2018-05-02 by UNKNOWN CODE

There is a commercial job that requires air vents no direct draining i need to put a hand sink and doublewash tub in can i connect those two drains into the 1 1/2 drain pipe from another wash tub already going into the air vent or do i have to bring a new 3 inch drain and air gap vent over to the new tubs?

On 2018-05-01 by (mod) -

You generally don't want a line to be dead flat as condensate could accumlate and in a cold area, freeze.

Use the search box found above and find our article on DRAIN FIXTURE UNITS and you'll see how to calculate how many fixtures can go onto a single vent line depending on size and the amount of water each fixture uses.

On 2018-05-01 by Anonymous

How about running from sink to tub and toilet then out roof? Can you tie them in this way? If so would I need to run pipe flat on the rafters or angel it just a little up to where it's going to vent out roof?

On 2018-05-01 by (mod) -

Nope. Straight up is fine.

On 2018-05-01 by Anonymous

Do you need to run the vent line at an angel or not

On 2018-04-03 by (mod) - moving a shower drain two feet - can still be vented OK

Jimmy's shower drain installation (C) InspectApedia.comMoving a drain 2 ft ought not itself to cause a problem IF you maintained 1/8" to 1/4" per foot slope. If your drain slopes properly then I suspect the problem is a partial blockage or inadequate venting.

On 2018-03-25 by Jimmy Doyle

I’ve recently installed a basement shower where there used to be a bathtub.

We moved the drain approx 2 feet to accommodate this. The drainage is now very poor on occasions but perfect at other times.

I’ve been told this may be a venting issue but the previous bathtub drain did not gabevthis issue. I put new tiles over this and can’t rip them up to access this. Is there any other possible fix?

On 2018-01-25 by (mod) - what's wrong with a too-steeply-sloped drain line?


If the drain pitch is too steep, when a toilet is flushed the water can flow so fast that it leaves the solids (feces, toilet paper) behind, leading to a clogged drain. With optimum pitch the water and solid waste flow together.

On 2018-01-25 by charles

what is the downside of having a "too steep" drain line?

On 2018-01-03 by Dave. H.

I want to add an addition with living space and windows roughly the same level as the soil vent stack about 10 away on the existing building roof the new roof with plumbing is three feet taller than the existing building. What must the vent height be?

On 2017-12-27 by (mod) - proper height for a basement and washer sink vent?

It should be above the flood rim of the sink

On 2017-12-26 by Roger

How high above a planned new basement kitchen sink, below a window, does the 1 1/2" pvc vent pipe have to be...before running horizontally?

Currently this basement room is a laundry. Plan to move wash tub and washer and remodeling room to a small kitchen. Currently the wash or laundry tub was "T"ed into a vent pipe 66" from that HIGH enough?

On 2017-12-19 13:35:12.449507 by (mod) -

Yes I'd add a second roof vent, that's perfectly permissible.

On 2017-12-19 01:47:28.289291 by Steve

I'm creating an upstairs apartment. I'll be tying in to the downstairs building drain. It's distant, so I'm wondering if I should vent the upstairs separately. In other words, is it ok to have 2 roof vents? Thanks!

On 2017-12-03 12:49:48.574199 by Nick

I should have said what state New Jersey National Standard plumbing code further checked it I can use a common Chiminey as can you thank you for your reply

On 2017-11-30 02:11:06.091136 by (mod) -

Yes, in many jurisdictions, you're allowed to vent a gas Appliance into the same flu.

Usually the gas vent is below the flu opening into which the oil fired Appliance vent connects.

Of course you don't say where you live and codes could be different for you. If you search this website for articles on shared flues you can find Details.

On 2017-11-30 00:11:40.184736 by Nick

Can you put a gas flu from a water heater in the same chimney that you have an oil boiler going into

On 2017-10-17 23:44:59.220897 by (mod) -

I don't know, Jim, what you describe isn't a product I've heard about.

On 2017-10-17 15:36:30.746211 by jim

Looking look through the roof vent I see at about16 inches deep ,what looks like a piece of metal on an angle in the pipe. It has about a two inch opening in a "v" like shape. What is this? This pipe vents the bathroom.

On 2017-09-17 22:49:05.267480 by (mod) -


Thanks for the astute question. No there is no valid reason for that angle, and worse, using a pre-fab stack vent boot flashing with the vent pipe at an angle as shown means that leaks are likely. That simply was how the plumber cut the hole and routed the vent stack out through the roof. She should have routed the vent vertically not at an angle.

On 2017-09-16 23:49:50.574267 by Caper

The vent stack in the photo at the top of this page appears to be more or less perpendicular to the slope of the roof rather than vertical. Is there a reason for this?

On 2017-09-03 21:36:24.172194 by alton

How many sewer vent pipes do you need for a 800 square foot home new construction.

On 2017-06-29 15:44:28.278970 by Sandra-Tucson AZ

What is the minimum height for a commercial rooftop plumbing Vent stack? What is the minimum distance it should be from the hvac unit?

On 2017-06-15 14:18:10.280733 by Gary

I need to add a sink to a room. The nearest wet stack is 12'-14' feet away. I am thinking of furring out the wall and arming over to the stack. My question is this. does the 2015 national plumbing code permit arming over that far?

On 2017-05-19 20:57:30.416653 by (mod) -


My opinion is that a plumbing vent could be concealed inside of a concrete wall just as it could be concealed inside of a framed wall. However there are some differences. One is that if is a Plumbing Leak that needs repair it will be very difficult to access in a concrete wall. Who is unlike running event in a wood-framed wall, event pipe run inside of a concrete wall May interfere with the structural design of that well. Be sure to check with your engineer or architect

On 2017-05-19 16:39:27.812333 by canerakcay

Vent can conceal concrete wall? what is the side effects if its conceal in concrete wall? which type of buildings i can install expose vent? is there any code requirements for expose or conceal?

On 2017-05-04 22:08:23.919912 by (mod) -

Tim in the article above see the
Tables of Plumbing Drain Pipe & Vent Pipe Sizes & Critical Distances to Plumbing Fixtures

Also see the calculations at PLUMBING DRAIN FIXTURE UNITS DFUs -

On 2017-05-04 22:04:19.649228 by Tim

How many Fixtures can you put on a 3" vent. What is the furthest distant you can be away from the vent?

On 2017-05-03 23:07:18.491640 by (mod) -


See where we discuss the size of vent pipe needed.

On 2017-05-03 10:43:58.910877 by Richie

Can I rough in a double vanity with a 1 1/2 pipe

On 2017-05-03 04:45:35.792073 by Tom

Question: I am finishing our DWV on my own after a plumber did the under slab work. The kitchen sink is about 20 It upstream and its AAV vented 2" drain passes a bathroom sink about 4 feet away from the trap of the bathroom sink. The code mentions only dry vented bathroom group fixtures fur use in wet venting the bathroom sink.

Can the kitchen sink drain be a wet vent for the bathroom sink? The other bathroom drains that might be wet vents are not accessible. So I am think the bathroom sink might have to have a dry vent. IPC governs.

On 2017-04-30 15:39:20.854988 by David

What side of the trap does the sewer vent pipe get installed?


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