Need help if I've vented my plumbing correctly for 3 bathrooms

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jef023

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Edit: I added a clearer diagram, and another diagram of multiple WC on a single vent.

Hi everyone,
4 years ago I purchased a 30yrs abandoned home and started doing its remodel. The house is 1 level on a concrete slab and all the plumbing was Cast Iron for drains and galvanized pipes for water. I've replaced all with sch40 PVC for drain and CPVC for water.

I'm in the final stage of the remodel: 1 half bath to full bath conversion, and 2 full baths remodel with a freestanding tub addition.

It's all DIY and I've actually completed the plumbing work, and hoping this community will tell me if I can go to next step of tiling, or point to some things I may need to fix.

My concerns are mostly around venting. I'm not sure If I've vented the plumbing properly. I used existing vent that were already there in the concrete roof, and eliminated 1 vent right before the S2 symbol, as I only discovered the vent pipe after the fact. The drain between S1 and S2 is new, hence I though Vent1 would suffice.

Please take a look at the diagram below. Are the 2 vents, and AAV enough for the plumbing? If no, where should I place a vent, or preferably an AAV to fix any issues you see?

The main pipe is 3"
The shower drains are 2"
The Vanity drains are 1.5"

I live outside the US where I don't need to get this inspected, but would still want to make sure what I've done is right. I know I should have asked first, but only recently I thought about it.. Better late than never.

Legend:
c/o: closeout
VS : Vanity Sink
WC : Water Closet
S : Shower
BT : Bath Tub
AAV: Air Admittance Valve
~1 : 1.5" Vent
~2 : 2" Vent

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plumbing_casa_360.jpg
Screenshot 2023-11-07 at 9.01.00 PM.png
 
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Jeff H Young

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why the odd abriviations vs1??? vanity sink maybe and the one all the way up hill has no vent ? thats odd is the trap below the floor too ? the dry vent below Wc1 looks wrong too . you have the drains all going down into a dead end then slightly upstream a wye thats wrong too
 

wwhitney

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Response based on the IPC, which is more lenient than the UPC. Going fixture by fixture, and just looking at the connectivity and sizes, not the lengths:

- VS1 needs a vent or AAV. You've drawn an S-trap, which is not allowed.
- Once you fix that, WC1 is then wet vented by VS1, OK.
- Dry vent takeoff just after WC1 not necessary (beyond needing some vent through the roof) but OK.
- S1 is wet vented by VS1, the IPC does not restrict order of fixtures on wet vent, OK. But is that showing an additional dry vent coming off S1 before it joins the 3" building drain? That would dry vent S1, if the dry vent is run properly. That means the dry vent coming off at least 45 degrees above horizontal, and rising at that angle or greater until at least 6" above the fixture flood rim. In other words, horizontal dry vents can't be under the slab. But none of that dry venting is required, so if it doesn't comply, you can just ignore it.
- VS1 can wet vent WC2 and S2 as well, as the IPC allows 2 bathrooms on a single wet vent when they are on the same floor, OK
- VS2 and VS3 are dry vented, OK
- WC3 and S3 are not properly vented. Wet vents are limited to 2 bathrooms, and this is the 3rd. One option is to separate the drainage from VS2 and VS3 from the 3" building drain and create a parallel drain that goes VS2/VS3, then WC3, then S3, then combines with the 3" building drain. That lets VS2/VS3 wet vet WC3 and S3.
- VS4 and VS5 are vented via the AAV, OK.
- BT could be wet vented via VS4 and VS5, but that requires a 2" drain from VS4/VS5, since the wet vent is carrying 2 fixtures, not just one. Upsize that drain to 2", and it's OK.

Now, as to lengths, for the wet vents of S1, S2, possibly S3 if you add the parallel drain, and BT if you fix VS4/VS5 drain size, the trap arm is regulated (but not for WCs). The trap arm for a wet vent goes from the trap outlet to the wye where the fixture drain joins the wet venting drain. So for example for S2 that would be the drain from the trap to the wye where it joins the 3" line.

The trap arm is limited to one pipe diameter of fall, and must fall at least 1/4" per foot. So if you get the fall exactly 1/4" per foot, you can have up to a 6' trap arm on a 1-1/2" trap, or up to an 8' trap arm on a 2" trap.

Cheers, Wayne
 

jef023

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Response based on the IPC, which is more lenient than the UPC. Going fixture by fixture, and just looking at the connectivity and sizes, not the lengths:

- VS1 needs a vent or AAV. You've drawn an S-trap, which is not allowed.
- Once you fix that, WC1 is then wet vented by VS1, OK.
- Dry vent takeoff just after WC1 not necessary (beyond needing some vent through the roof) but OK.
- S1 is wet vented by VS1, the IPC does not restrict order of fixtures on wet vent, OK. But is that showing an additional dry vent coming off S1 before it joins the 3" building drain? That would dry vent S1, if the dry vent is run properly. That means the dry vent coming off at least 45 degrees above horizontal, and rising at that angle or greater until at least 6" above the fixture flood rim. In other words, horizontal dry vents can't be under the slab. But none of that dry venting is required, so if it doesn't comply, you can just ignore it.
- VS1 can wet vent WC2 and S2 as well, as the IPC allows 2 bathrooms on a single wet vent when they are on the same floor, OK
- VS2 and VS3 are dry vented, OK
- WC3 and S3 are not properly vented. Wet vents are limited to 2 bathrooms, and this is the 3rd. One option is to separate the drainage from VS2 and VS3 from the 3" building drain and create a parallel drain that goes VS2/VS3, then WC3, then S3, then combines with the 3" building drain. That lets VS2/VS3 wet vet WC3 and S3.
- VS4 and VS5 are vented via the AAV, OK.
- BT could be wet vented via VS4 and VS5, but that requires a 2" drain from VS4/VS5, since the wet vent is carrying 2 fixtures, not just one. Upsize that drain to 2", and it's OK.

Now, as to lengths, for the wet vents of S1, S2, possibly S3 if you add the parallel drain, and BT if you fix VS4/VS5 drain size, the trap arm is regulated (but not for WCs). The trap arm for a wet vent goes from the trap outlet to the wye where the fixture drain joins the wet venting drain. So for example for S2 that would be the drain from the trap to the wye where it joins the 3" line.

The trap arm is limited to one pipe diameter of fall, and must fall at least 1/4" per foot. So if you get the fall exactly 1/4" per foot, you can have up to a 6' trap arm on a 1-1/2" trap, or up to an 8' trap arm on a 2" trap.

Cheers, Wayne
-Thanks for the clear and very helpful message.
-I will add an AAV at VS1 ( I was thinking of converting C/O1 to a dry vent), but the AAV is much better.

-I know that codes were written for good reasons and I want to follow them, hence why I'm posting here. But is it really a bad idea to wet vent more than 2 fixtures? If yes, I can eliminate VS3, as it is a small vanity in a toilet closet that is not truly needed.

-Is it really a bad idea to wet vent BT with the 1-1/2" wet drain? We've already poured cement, but if its really a bad idea, I'll break it and change the pipe to a 2" pipe. An option would also be to add an AAV at BT. Just wondering if the 1-1/2" can pass, or 2" is a must.

- I did verify the 1/4 per foot drain.

-I appreciate the very detailed breakdown. Do you offer virtual consulting services?
 

wwhitney

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I take it the project is outside Puerto Rico, since you said it was outside the US? Puerto Rico does use the IPC.

Also, I see in the OP you posted a diagram about circuit venting. That prompted me to check the rules in the IPC, Section 914:


I'm not as familiar as those rules, so my comments are somewhat provisional. But with a couple caveats I think your layout mostly complies with Section 914 on Circuit Venting.

First, if you deleted all the vanities, then the 3" line definitely counts as a circuit vent. You've got 7 fixtures (3 WCS, 3 showers, one bath tub), under the maximum of 8. You don't have 4 WCs, so you don't need a relief vent. And the total DFUs is 17, under the 20 DFUs allowed on a 3" horizontal branch drain. You would just need to confirm that the bath tub trap arm is not too long--it would be measured from the tub trap all the way to the 3" line, and is limited to 6' with 1-1/2" of fall if the tub trap is 1-1/2", or 8' with 2" of fall if the tub trap is 2".

Now, of course, you do have the lavatories. They need to be individually vented (VS1) or common vented (as pairs, i.e. VS2+VS3 and VS4+VS5), as their traps are above the floor, and so their vent connections need to be above the floor (within at most one pipe diameter of fall from the trap). 914.5 does allow such fixtures to discharge to the horizontal branch drain that is serving as a circuit vent.

However, you now have an issue with the bathtub. You can't wet vent via the lavs (ignoring for the moment that the 1-1/2" lav drain with 2 DFUs is too small to serve as a wet vent), because 914.5 requires individual or common venting. You could add a vent (dry vent through the roof or an AAV) to the tub trap arm, that would take care of the problem. It should be between the trap outlet and where the tub drain joins the lav drains. If you use an AAV, it would need to be at least 4" above tub trap arm (IIRC, from the manufacturers instructions) and would need to be accessible for service and open to room air.

There's one other potential problem with the circuit vent, namely that you have 22 DFUs total. A 3" horizontal branch drain is limited to 20 DFU. In contrast, a 3" building drain with 1/4" per foot of slope can handle up to 42 DFUs. But the rules in IPC 914 on circuit venting all refer to a horizontal branch drain. So I think that would mean that if you are using the 3" building drain as a circuit vent, the portion that is a circuit vent would be limited to 20 DFUs. The obvious solution to that issue would be to add an individual vent (dry vent through the roof, or AAV) to the shower S3 trap arm.

So that's the upshot, I'm fairly sure that if you add individual vents to S3 and BT, then all the WCs and the other showers will be properly circuit vented.

Cheers, Wayne
 
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