Wet Vent Takeoff Argument

[BackwardsPTrap]

One thing I'm having a hard time finding information on is how to properly connect fixture drains to a wet vent. So many diagrams I see in books and online show a wet vent setup where fixture trap arms dump into the wet vent at a downward 45° angle. This doesn't make any sense to me. Isn't this creating a siphon by dumping downwards before the trap arm is vented? See the following two examples:

How can you downturn any trap arm before it being vented, without creating a siphon condition? In both of these examples, the pipe drops below the weir before being accessible to the vent air. Here is a side view example of the condition shown in the images above.

I believe this is done because people misinterpret IRC 3104.3 indicating that vents must have a 45° takeoff from horizontal. But that still doesn't make sense because they are angling the drain, instead of the wet vent...

So what is the right way? Is it acceptable to simply connect to a wet vent along the same plane as the wet vent slope (1/4" per foot)? Don't the wet vent pipe sizing regulations account for waste flowing through the wet vent and make sure the pipe is big enough to allow both waste and airflow? Like this:

Dry vents need to have a 45° takeoff because waste can clog them if laid flat. But a wet vent will have water flow from the fixtures upstream, so there's no reason to have the 45° takeoff. Am I right on this guys?

 

[Terry]

Those books that show the trap arms dumping down at an angle are wrong.

 

[Sponsor]

 

[Terry]

Drawings from a UPC plumbing inspector in Seattle.

A very basic drawing. Trap arms on the horizontal, and those should be wye fittings not santees.
Wyes on the horizontal and santees on the vertical.

A washer isn't part of the bathroom group allowed to be wet vented. Those get their own vents.

 

[FullySprinklered]

The rules are the rules. You're better off not getting into a pissing contest with the city/county inspector. Ain't worth it.

However, any fixture with a residual trickle-down flow after the fixture is used, could refill the p-trap and prevent the passage of sewers gasses into the living space.

For example; if you take a tub bath, the outflow from the tub would suck the trap dry if it's not done to code. Now if you take a shower in the same tub, the trickle-down from the tub/tile/body would tend to refill the trap after the water is turned off, mitigating the perils caused by the crappy plumbing.

Throw in a half pint of urine, and you're good to go.

 

[FullySprinklered]

How about a clothes washer? The last thing that happens on a wash cycle, where water is concerned, is a spray of water to rinse the load, not enough to compromise the trap as it runs down the drain. ( much of my last post disappeared for some reason, so I'm splitting up my post).

The main wash cycle? Yes, a lot of water flowing out fast. Rinse cycle? Not so much.

Could any sewer gasses escape because of the S-trap situation. You bet. It would be about like inviting your in-laws over for a burrito dinner.

Not bad enough to warrant replumbing the house.

 

[hj]

Not everyone who writes a book knows what he is talking about.

 

[Reach4]

How about a clothes washer? The last thing that happens on a wash cycle, where water is concerned, is a spray of water to rinse the load, not enough to compromise the trap as it runs down the drain.

That's a point I have thought about, but I have not seen that written before. If you see a washer draining into a laundry tub, you will see the last water comes out in dribbles and drips.

BackwardsPTrap, the toilet is not a problem, because the trap is in the toilet itself and gets refilled during the flush process.

 

[Terry]

Why would anyone installing new pipes not go the distance and do it right? The reason we have these codes and our inspectors is to make sure that what is buried in floors and walls works. Not maybe works, but actually works all the time.
We're not going to hand out advice that says to just wing it. Our family cabin on Lake Quesnel had an outhouse. It worked fine, but I like indoor plumbing much better.

This works too.

 

[BackwardsPTrap]

Thanks for the advice guys. For context, I'm planning out a new bathroom, not repiping an existing layout. I initially was going to bring two vent stacks up, but due to wall constraints I was hoping to configure as a wet vent with a single stack, so that led me down the rabbit hole.

 

[Mike Garrod]

A wet vented Portion of pipe can’t reduce in size and toilets need to be furthest downstream wet vented fixture. Npc Canada code

 

[Master Plumber Mark]

I think I have done it both ways many times over the years ... both will work
because an 1 1/4 pipe cannot overfill a 2 inch drain line and siphon out a line...anyway

it is more just depending on the layout and the amount of fall available..
in all honesty both ways will work .... it really all depends on the fall you have .

inspectors in our town are too stupid to really know what they are looking at anyway

 

[Sylvan]

I am sticking with the NYC 1968 plbg code NO WET venting . A lot more stringent then the code the state adopted

 

[Master Plumber Mark]

I am sticking with the NYC 1968 plbg code NO WET venting . A lot more stringent then the code the state adopted

Hey...Whatever thrills you...
we have been wet venting in this state since the 50s
and there has never been an issue....and I dont think that there ever will be....

Of course wet venting makes the work a lot less expensive for both materials and labor
and perhaps where you are located, it keeps and protects your job...
.by making the job more complicated that it could be and keeping the hacks out...

their are a lot of little shires and fiefdoms where permits are required just
to install a water heater for this reason....to keep only plumbers doing the work....