# Floor drain with no vent



## olc

I have seen this a couple times recently. 
A floor drain installed with a trap and then the drain is piped immediately back down to a horizontal sanitary main which is entirely below the bottom of the trap.
The trap is not vented. Am I missing something?
If the outlet of the trap were down at the same level as the sanitary main and the piping was installed such that there was a wet vent or circuit vent, then the trap would be vented. 
In the photo the trap to the left is for a floor drain. There is another one in the back of the room which is vented.


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## OldSchool

Just because you seen it does not mean it is to code......

This is not to our code


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## LEAD INGOT

That's just a big old s-trap. This was brought up at a code seminar about 7 years ago when we changed to UPC. The state said that that is how they wanted it. My local plumbing inspector and I agreed that it was B.S. and an s-trap.


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## futz

olc said:


> I have seen this a couple times recently.
> A floor drain installed with a trap and then the drain is piped immediately back down to a horizontal sanitary main which is entirely below the bottom of the trap.
> The trap is not vented. Am I missing something?


Ya it's not vented. It is an S-Trap. But, as I was told by an old plumber when I was a young apprentice, "a floor drain or a bathtub (and some large showers) are really kind of self-priming fixtures". Sure they'll siphon till they're almost empty, but the remaining dribbles will refill the trap seal anyway. :laughing: Hey, I didn't say it, and I'm not sure I really totally believe it, nor do I pipe things to rely on it. But there is some truth to it for sure.

It's unlikely any floor drain, especially with that large a trap, will ever see a large enough volume of water in one big gulp to cause it to siphon. And if it did, the remaining dribbles would very likely refill the trap seal. Therefore I don't think it's much of an issue. The biggest problem we see with large FD traps here is them drying out when not being used, something that a vent would exacerbate anyway.


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## smellslike$tome

Do ya'll not have trap primers installed on your floor drains? Even if it doesn't siphon it will probably dry out if there are no overflows from the bathroom or backups from the sanitary. I'm pretty sure IPC (which is what I'm under) requires a trap primer. I say pretty sure because I haven't touched a code book in quite some time. It might be time for a refresher.


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## futz

smellslike$tome said:


> Do ya'll not have trap primers installed on your floor drains? Even if it doesn't siphon it will probably dry out if there are no overflows from the bathroom or backups from the sanitary. I'm pretty sure IPC (which is what I'm under) requires a trap primer. I say pretty sure because I haven't touched a code book in quite some time. It might be time for a refresher.


Here they removed the requirement for trap primers, in residential at least (I'm not sure about commercial - been out of it for too long). I guess the primers were causing far more problems than smelly floor drain traps in mechanical rooms did, so they're not not required by code anymore.


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## Widdershins

That would have been fine if it were for emergency use only and if the wye had been rolled down onto its side.

It looks to me like somebody got lazy and didn't want to dig down deep enough to bury the trap.


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## Adamche

futz said:


> Ya it's not vented. It is an S-Trap. But, as I was told by an old plumber when I was a young apprentice, "a floor drain or a bathtub (and some large showers) are really kind of self-priming fixtures". Sure they'll siphon till they're almost empty, but the remaining dribbles will refill the trap seal anyway. :laughing: Hey, I didn't say it, and I'm not sure I really totally believe it, nor do I pipe things to rely on it. But there is some truth to it for sure.
> 
> It's unlikely any floor drain, especially with that large a trap, will ever see a large enough volume of water in one big gulp to cause it to siphon. And if it did, the remaining dribbles would very likely refill the trap seal. Therefore I don't think it's much of an issue. The biggest problem we see with large FD traps here is them drying out when not being used, something that a vent would exacerbate anyway.


It is what we call "trailing waste" and all fixtures have it ,except for basins and bidets we have strict regulations on them to protect the trap seal. You are right about the floor waste - you would need a room full of water to start a siphon.


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## Tommy plumber

The wye should've been rolled on its side.


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## user8031

Just viewed the photo. This is very sloppy and not a correct installation obviously. AWFUL work my friend.


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## ILPlumber

Aww Crap!! I got the main directly under where the floor drain is drawn!

Oh well.....


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## 422 plumber

that right there is just chimptastic.


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## J.d.

Here in BC, using the canadian national plumbing code. floor drains 3" + do not require a vent as long as the trap arm exceeds 18" in length and does not have more grade than 1/4" per foot. That would not pass inspection here.


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## Radium

J.d. said:


> Here in BC, using the canadian national plumbing code. floor drains 3" + do not require a vent as long as the trap arm exceeds 18" in length and does not have more grade than 1/4" per foot. That would not pass inspection here.


18 feet is what you meant right.

Sent from my iPad using PlumbingZone


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## Dmaz

Radium said:


> 18 feet is what you meant right.
> 
> Sent from my iPad using PlumbingZone


Minimum 18", to prevent trap siphoning.


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## Boomer!

That is considered a S trap according to IPC, even if the main branch was directly in line F/D the riser could have been offset above it to mate it to the proper location. I do believe that even on an emergency F/D it has to be vented correctly but not accounted for on the total DFU.

No offense, I would have made my guys cut all that out. It looks like someone was throwing a can of primer around playing catch with it.


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## Radium

Dmaz said:


> Minimum 18", to prevent trap siphoning.


That's right, my mistake.

Sent from my iPad using PlumbingZone


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## Dave C.

a floor drain 3" and larger need not be vented when underground ,the other one is probalby a fixture which required individual vent,however the floor drain is piped wrong creating an s-trap min 2'-0" when jumping up off a lateral,2xD when horizontal off vertical in my area


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## moonapprentice

It still needs to be vented underground. Maybe not an individual vent, but somehow vented. C.d.w.v is an option to eliminate that vent but requires an oversized sewer with rules to the size of vent that is venting that u.g. trap


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## bdaltonph

That's defiantly wrong. Plus the three ferncos under the slab would also be a fail where I'm at. If nothing else the guy should be fired for primer mess! Geez, was this his first doing this?


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## Flyout95

Why are we bumping old posts for no reason?


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## moonapprentice

New guy bumped a few already. I'm Rollin with it since lately it's been slow, then the password reset really did some damage. I hear what your saying, but maybe it's good to keep it a little active even if they are old. Just my 2 cents


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## bdaltonph

Oh man I got suckered into a 3 1/2 year old thread.


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## wyrickmech

Ok I will bite. The only thing that requires a vent is something that has a dfu. In my code book the only thing that does not require a vent is a floor drain in a area such as a floor drain in a locker room at a ice rink. A floor drain in a bathroom is another one, any floor drain for emergency removal of water dose not require a vent. The size has nothing to do with the venting other than what size of vent. And any trap that crosses the weir without either increasing size or being vented is a s trap and is illegal.


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## Dave C.

moonapprentice said:


> It still needs to be vented underground. Maybe not an individual vent, but somehow vented. C.d.w.v is an option to eliminate that vent but requires an oversized sewer with rules to the size of vent that is venting that u.g. trap


underground floor drains 3" and larger need not be vented,if you jump up off a main and go horizontal agian it needs at least 2'-0" of pipe before the drop back down to the main to vent it self.... mains are designed to run 1/3 full at max which leaves 2/3 air so the piping will vent itself, fixture above ground ,need venting because of the basic negative pressure created on the system with waste falling down a stack that is why we vent,with that being said i dont agree with fixture traps in underground needing an idividual vent becaus a trap doesnt know what you have hooked to the top of it, and all will drain correctly ,but that is code so as i do :thumbsup:


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## Dave C.

wyrickmech said:


> Ok I will bite. The only thing that requires a vent is something that has a dfu. In my code book the only thing that does not require a vent is a floor drain in a area such as a floor drain in a locker room at a ice rink. A floor drain in a bathroom is another one blackly any floor drain for emergency removal of water. The size has nothing to do with the venting other than what size of vent. And any trap that crosses the weir without either increasing size or being vented is a s trap and is illegal.


 dont understand the last part of that statement its getting late


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## wyrickmech

Dave C. said:


> dont understand the last part of that statement its getting late


 ok when you turn down you can either increase to self vent or break the vacuum with a vent of the proper size.


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