Hello,

I've got a 4" stack in a 3-storey house and I'd like to run the following into it:
1st Floor: 2 kitchen sinks (back-to-back 2")
2nd Floor: 2 toilets (back-to-back 3"); 2 lavatories (1.5"); 1 bathtub (1.5")
3rd Floor: 1 toilet (3"); 1 lavatory (1.5"); 1 bathtub (1.5")

Is this OK, or is it too much stuff on the stack? The kitchen sinks and lavatories will be vented above the highest fixture on the 3rd floor. Do the bathtubs need to be vented, or does the overflow act as a vent? If the bathtubs need to be vented, how do you vent them if they're draining into the 3" toilet lines via 3x1.5 tees?

Thanks for your help!

Regards,
Lou

Typical 4" vent stack can carry up to 256 plumbing units . Value of individual plumbing units assigned to residential plumbing fixtures - as present in your house - are :

3 Toilets x 3 plumbing units each = 9 plumbing units
2 Kitchen sink x 2 plumbing units each = 4 plumbing units
3 Lavatory x 1 plumbing units each = 3 plumbing units
2 Tub x 2 plumbing units each = 4 plumbing units

Total vent load per 4" stack vent: 20 plumbing units

Therefore, you are safe with connecting your listed plumbing fixtures to one, 4" stack vent.
But in any case, it is a good practice to check with you local building department before you do anything. Good luck !

Hi Lou:

YUP! Milo said it! You can practically fit a HOTEL on a 4" waste stack... ;)

Now, in terms of the tubs... yes, they need to be vented and you use a 3" x 1.5" WYE fitting. No sanitary tee fittings on horizontal drain pipes... period!

However, you need to know that a typical bathroom has only 1 two inch vent that vents the entire bathroom if can be piped a certain way.

Here, you pipe 3" to toilet, then take a 3" x 2" wye off the 3" line (just behind the toilet elbow) and run the two inch over to the tub and the lavatory.

Reduce the tub waste to 1.5" and pick up tub, and then run the lavatory 2" all the way up to the vent you will be connecting into... you need to stub out 1.5" for lavatory via a 2"x 1.5" sanitary tee fitting (allowed on vertical waste piping).

This is what they refer to as WET VENTING and it is accepted in most states/towns in the country!

However, you do need to check to be sure that this is allowed in your area.

Again, 2" lavatory vent acts as a wet vent for the tub and the toilet and as a regular vent for itself... hope that makes sense.

Otherwise, can also vent toilet using the wet vent from the lavatory and then just add an individual 1.5" vent for the tub (here would add a 1.5" sanitary tee fitting (allowed as a vent fitting, rolled above centerline of waste line) off the 1.5" tub drain within a few feet of tub itself).....lavatory vent would still need to be 2" all the way to where vents connect 2" or larger.

Hope that answered your questions... hope it didn't just confuse you more... ;)

Let us know if you need more information...

MARK

Hey Lou,
Milo nailed it with the fixture units and Mark nailed it with the set up.

Quote:

---

Do the bathtubs need to be vented, or does the overflow act as a vent? If the bathtubs need to be vented, how do you vent them if they're draining into the 3" toilet lines via 3x1.5 tees?

---

Back in the 20's and 30's that's exactly how bathtubs vented themselves. Gurgle, gurgle. Gurgle through the overflow. Nowadays we wet vent out tubs as Mark pointed out. Most bathroom groups are roughed in like this.
Toilet connects to sewer main or the stack vent. Lavatory connects to toilet drain and runs a vent off the top the stubout tee out the roof or revents back into a dry vent in the attic.. The toilet wet vents through the lavatory vent and the tub/shower connects to the lavatory drain and is wet vented by it. This is a normal rough in and is acceptable both by local and state codes and also The Standard Plumbing Code Book in 90 percent of the country. Check your local codes.to make sure you're not in the excluded 10 percent.. The vent off the lavatory may be run out the roof or revented back into a dry vent in the attic or if you're reventing back into a fixtures dry vent you must make your connection at least 6 inches over that fixtures flood rim.Good luck, Tom

Thanks to everyone for their excellent information!

Mark, I think I've got to use your suggestion below:

[QUOTE=massplumber2008]
Otherwise, can also vent toilet using the wet vent from the lavatory and then just add an individual 1.5" vent for the tub (here would add a 1.5" sanitary tee fitting (allowed as a vent fitting, rolled above centerline of waste line) off the 1.5" tub drain within a few feet of tub itself).....lavatory vent would still need to be 2" all the way to where vents connect 2" or larger.

You see, two of the bathrooms are retrofits, and I'd like to keep everything in the same spot. That is, all 3 fixtures along the same wall, with the toilets in the middle, going right into the stack via a 4x4x3x3 back-to-back fitting (not sure of the name). Unfortunately, the original tubs weren't vented. One of the tubs still has an old-school lead drum trap on it. It's gonna be tricky, but I should be able to fit a 1.5" PVC glue trap and a vent tee in there somewhere.

So, if I use Mark's "otherwise" option quoted above, is it necessary to wet vent the lavatory? I mean, can I drain the lav into the main stack above the toilet via a 4" x 1.5" tee and just run a typical dry vent off the top of the lav tee? Would the 1.5" vent off the tub be sufficient to vent the toilet? Do the toilets need venting at all, as they are very close to a 4" stack?

Again, thanks for your help!

Regards,
Lou

Hi LOU:

If that lavatory is on the top floor then you can just add the 4"x1.5" sanitary tee fitting and lavatory is vented.

Asumming the tub will connect into the 3" toilet drain line at top floor, you must not only vent the tub but are required to increase the drain and vent to the tub to 2" in this case as the tub vent will act as a wetted vent for the toilet. The drain reduces to 1.5" after the vent, the vent continues 2" and can connect BACK INTO THE 4" STACK 6 inches above the FLOOD LEVEL RIM OF THE LAVATORY if convenient or can be run up to attic and connected up there.

Basically:

1st floor... 1 - 1.5" vent

2nd floor... if back to back, may just need the 2" wet vents from the lavatories for each bathroom.

3rd floor The one 2" vent as mentioned and the 4" stack above the toilet is vent for the lavatory.

Here is a picture of a basic bathroom using a wet vent... look at waste and then vent and see if makes sense. NOTE that the picture does not show the WYE fitting required for all horizontal connections into a drain line.

This picture represents what I am picturing for your 2nd floor bathrooms, except your toilets are back to back and I assume the lavatories and tubs are not (because you did not say they were)... so I think you want to apply this picture to BOTH bathrooms on the 2nd floor.

Otherwise, if back to back at toilets and back to back at the lavatories you may get away with just 1 - 2" wet vent from the back to back lavs. To vent all fixtures on the second floor.

Hope this makes sense.

Let me know if you need anything else... ok?

Have a good day... MARK

Hey, guys, I see this problem in the drawing in post #6:

1. Tub needs vent, otherwise, it will try to draw air through overflow, making lots of gurgling noise in the process. I would rather omit sink drain in favor of tub drain.
2. If plumbed as shown in the drawing, than when you flush toilet, it will draw air from tub. Tub will gurgle.
3. Solution: Extend sink vent all the way to the tub area, install vent for tub.

Quote:

---

Originally Posted by Milo Dolezal

Hey, guys, I see this problem in the drawing in post #6:

1. Tub needs vent, otherwise, it will try to draw air through overflow, making lots of gurgling noise in the process. I would rather omit sink drain in favor of tub drain.
2. If plumbed as shown in the drawing, than when you flush toilet, it will draw air from tub. Tub will gurgle.
3. Solution: Extend sink vent all the way to the tub area, install vent for tub.

---

Milo,
Wouldn't the tub and toilet be wet vented by the lav vent? When we rough for a bathroom group in my area we wet vent our group through the lavatory and only run up a single vent. Does your code force you to run individual vents? Regards, Tom

Speedball1, good question. It is interesting how our installation practices change from state to state.

Our Plumbing Code forces us to install individual vents. They can be combined above anti-siphon level. That's about 42". But usually, we combine in the attic. Wet vents are disallowed. We consider wet-venting to be outdated type of installation. When we do remodels of old houses and run into wet vent situation we leave toilet hooked up to 4" stack-vent and run rest of the vents individually.

Tub almost always gurgles if not vented as it tries to draw air through its overflow.

M ilo,

Quote:

---

Tub almost always gurgles if not vented as it tries to draw air through its overflow.

---

And so it does as I pointed out in a earlier post.

Quote:

---

Back in the 20's and 30's that's exactly how bathtubs vented themselves. Gurgle, gurgle. Gurgle through the overflow. Nowadays we wet vent out tubs so that doesn't happen.

---

Quote:

---

Wet vents are disallowed. We consider wet-venting to be outdated type of installation.

---

Could you explain why wet vents are "out dated"? Regards, tom

Hey Lou:

Like Tom said... we have been doing it this way in Massachusetts and in Florida and many other states along the east coast for a very long time and never had a problem... just want you to be comfortable with that.. ok?

Of course, this is why I always advise people to check with their local codes enforcement people as I did for you at my first post to you, Lou (post #3)... ;)

The whole idea behind wet venting is that as long as knowone uses the lavatory when using the tub or the toilet, the lavatory vent (which usually only has to be 1.5", but has been increased to 2" vent for wet venting purposes here) acts as a full size or even an oversized vent (tub only requires 1.5" vent, normally..but here has a 2" vent) for the toilet, the tub and the lavatory.

There is no gurgling of tub or draining issues as there is always a vent within required distances from the vent to the trap at the fixture.

I don't know about people in Milo's area, but maybe they keep trying to bathe in the tub while trying to brush their teeth in the sink at the same time... and yes.. that would be a problem with the wet venting as presented... :p

We are still waiting on his response to Tom's questions. And Lou, as Milo said, codes do differ quite abit from state to state so do check all this with your local guys.. ok?

Anyway, Lou, I just wanted you to know that you whould be just fine with what I recommended above.

Let me know if you have any more questions...

MARK