DWV Feedback

[DGZ]

Hoping to get some advice on my DWV setup for a 8'x14' 2-story addition I have been building. I am the homeowner and am doing all the work myself. I'd say I'm about 90% decided on my DWV setup, but need to get some feedback for the last 10%.

Below is a rough sketch of my layout. Drains will be in a crawl space. 1st floor bathroom, 2nd floor laundry


View attachment 104243



My biggest dilemma is determining my proper vent layout for the1sr floor bathroom. I can’t dry vent each fixture separately due to framing and other limitations. I’ve known from the beginning I’d need to figure out a wet venting option. I’ve been back and forth in my head and at this point I don’t think I know what is up and what is down. Where does the vent need to attach to the 3” horizontal? Any feedback or other options are appreciated.

**Just to note: I’ve discussed a prior plan with my code inspector that I know was not the correct way to do and he approved it. So I’m not relying on him to confirm. He’s already passed my inspection just based on our discussion.

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[Reach4]

1. Lav needs a vent.

2. WM standpipe need a vent.

3. If you want to wet-vent the toilet, have the drainage from the WM inserted downstream of the bathroom stuff. If you insert before the toilet, as in your diagram, you will need to also add a vent for the toilet.

 

[Sponsor]

 

[DGZ]

@Reach4

1. yup....I can't dry vent from the lav so I need to determine a way to wet vent it.

2. the WM standpipe is vented. That is the dotted line going vertical after the WM and will tie into an existing vent stack.

3. WC doesn't have to be wet vented, just figured based on the setup it would be easier. How to design the connection point of the WC, WM, and the horizontal with the shower and lav is my hang up.

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How about if the WM inserts downstream on a 4" vertical.............the WC inserts just above that on the 4" vertical.......then there is an elbow that then connects to the horizontal that has the shower and lav.

Can I tie a dry vent into the horizontal to vent the shower and lav, if so where would it go? Would this vent suffice for the toilet too? The vertical dotted line in the diagram below indicates the dry vent connecting above the WM and this would be the vent I'd need for the WC, shower, and lav.

 

[Reach4]

That drawing works, as long as the lav is vented TTR (thru the roof) or AAV. I presume lav, shower, and WC are on the same floor. If the WC is in the basement, it should get a vent too.

Use 2-inch pipe or bigger from where the lav is vented to the toilet. Use 3 inch or bigger from the toilet onward.

 

[DGZ]

That drawing works, as long as the lav is vented TTR (thru the roof) or AAV. I presume lav, shower, and WC are on the same floor. If the WC is in the basement, it should get a vent too.

When you say vented through the roof.....do you mean by the vent indicated by the dotted line or a vent coming off from the lav fixture drain? I thought about venting the lav with an AAV, but if I could vent atmospherically that would be ideal. Any issues with the vent being upstream on the horizontonal from the lav insertion like below.

Yes the lav, shower, and WC are on the same floor.

Use 2-inch pipe or bigger from where the lav is vented to the toilet. Use 3 inch or bigger from the toilet onward.

My plan is 3" for the horizontal that the lav and shower is on. The vertical the WC is on will be 4".

 

[Reach4]

When you say vented through the roof.....do you mean by the vent indicated by the dotted line or a vent coming off from the lav fixture drain? I thought about venting the lav with an AAV, but if I could vent atmospherically that would be ideal. Any issues with the vent being upstream on the horizontonal from the lav insertion like below.

The dashed line seems to connect in the line to what I presume is the cleanout. The actual vent should be in the trap arm or a bit downstream. So a dry vent in the right place will be best.

Lavs are usually vented from above into a sanitary tee in the vertical plane. Below that santee is 2 inch pipe. Above the santee, the venting joining the other vents in the attic can be smaller than 2, often 1.5. This is not the only way, but it is the common way. What did you picture?

 

[DGZ]

The dashed line seems to connect in the line to what I presume is the cleanout. The actual vent should be in the trap arm or a bit downstream. So a dry vent in the right place will be best.

Lavs are usually vented from above into a sanitary tee in the vertical plane. Below that santee is 2 inch pipe. Above the santee, the venting joining the other vents in the attic can be smaller than 2, often 1.5. This is not the only way, but it is the common way. What did you picture?

Yes, the dashed line connects as you interpret. From your explanation I realize that is not the correct position.

The bathroom addition is slightly cantilevered over a girder so I cannot route the lav drain into the wall cavity as normally is done because the drain route below the sanitary tee would hit directly on the girder. This also means I can’t vent above as normally done either. I have to route the drain down through the floor like below.

**I am assuming having the trap arm length more than 2x the pipe size like a washing machine trap arm is sufficient to prevent this from siphoning like an s-trap. Correct me if that is incorrect.

From your statement I’m interpreting that the vent should be at either of the locations marked by the red line, correct?

 

[Reach4]

I am assuming having the trap arm length more than 2x the pipe size like a washing machine trap arm is sufficient to prevent this from siphoning like an s-trap. Correct me if that is incorrect.

Not correct. The minimum length of the trap arms to the vent is 2x the pipe size, but you need a vent for each. With an AAV, the AAV has to be at least 4 inches above the trap arm.
See AAV picture in https://terrylove.com/forums/index.php?threads/best-of-a-bad-s-trap-situation.84576/ #3

https://terrylove.com/forums/index....-with-dwv-and-venting-for-new-bathroom.98695/ #4

https://terrylove.com/forums/index.php?threads/wash-machine-drain-pipe-flood.110018/ #10

 

[DGZ]

That makes sense. My initial plan was to use an AAV to vent the shower and lav on a branch. Turns out I was on the right track to begin with. I'll add the AAV back into the lav drain plan.

Things that are determined:

1. I need an AAV on the lav trap arm because I have to route the drain through the floor due to being unable to vent directly into a dry vent through the roof.
2. The WM drain needs to connect downstream from the wc/shower/lav and may not act as a wet vent.

To be determined:

1. Can the lav AAV be used to vent the entire bathroom group (WC, shower, and lav) Essentially the shower and lav would be on a branch drain from the top of a short vertical stack.
2. Should I still put in a dry vent (dotted line) even with the AAV?

 

[wwhitney]

1) Yes. But your explanation of a girder below the wall doesn't explain why you can't run a vent up the wall to the attic if you prefer. If there is no obstruction at the top plate of the wall, you could run your drain/vent in the wall, except the very bottom portion, where the drain could 45 out of the wall to get around the girder.

2) The dotted line going to ??? is not necessary as a vent. The dotted line at the top of the laundry standpipe san-tee is a required vent. Above the san-tee, the vent needs to rise to at least 6" above the top of the standpipe before it turns. In the attic the vent can join an existing vent through the roof or go to a new roof penetration. [Actually you could use an AAV for the washer standpipe, too, if you prefer, as long as the existing building as a vent through the roof. Note that AAVs have to be accessible, so if it's in a wall, it requires a box with a ventilated access panel.

Cheers, Wayne

P.S. Wil the lav properly dry-vented, its drain can wet vent the shower. The shower trap arm is then the drain from the trap outlet to the wye with the lav drain. That trap arm is limited to one trap diameter of fall (presumably 2") while it must at least 1/4" per foot.

 

[DGZ]

1) Yes. But your explanation of a girder below the wall doesn't explain why you can't run a vent up the wall to the attic if you prefer. If there is no obstruction at the top plate of the wall, you could run your drain/vent in the wall, except the very bottom portion, where the drain could 45 out of the wall to get around the girder.

Being that I hadn't originally planned to go up I've installed dryer venting, water lines, and electrical already in the ceiling bays that would need to be modified. The lav is on an exterior wall (east wall) and would need to be routed through the 2nd floor joist system across to the conjoining wall (west wall) of the addition/existing house and then up the 2nd floor wall and turn into the attic. The 2nd floor ceiling on the addition is vaulted so I'm not really able to go all the way to the roof within the exterior wall where the lav is located (there is no attic space over the addition, only the existing house).

2) The dotted line going to ??? is not necessary as a vent. The dotted line at the top of the laundry standpipe san-tee is a required vent. Above the san-tee, the vent needs to rise to at least 6" above the top of the standpipe before it turns. In the attic the vent can join an existing vent through the roof or go to a new roof penetration. [Actually you could use an AAV for the washer standpipe, too, if you prefer, as long as the existing building as a vent through the roof. Note that AAVs have to be accessible, so if it's in a wall, it requires a box with a ventilated access panel.

Yes, the vent above the san-tee will be atleast 6".

Regarding an AAV for the WM standpipe......the bathroom/laundry addition is essentially a separate sewer branch from the existing house. I installed a new underground sewer lateral in my front yard inserting into the existing lateral. This was the simplest option considering I otherwise would have had to penetrate through my poured concrete basement walls and floor to insert within the existing house footprint. Knowing this, would an AAV for the WM standpipe still be an option? With an AAV for the WM the only atmospheric venting would be downstream through the sewer lateral connection in the front yard.

P.S. Wil the lav properly dry-vented, its drain can wet vent the shower. The shower trap arm is then the drain from the trap outlet to the wye with the lav drain. That trap arm is limited to one trap diameter of fall (presumably 2") while it must at least 1/4" per foot.

Is this referring to just a normal dry-vent going above the lav or for the AAV as well? Fall would be within limits.

 

[wwhitney]

With an AAV for the WM the only atmospheric venting would be downstream through the sewer lateral connection in the front yard.

With that information, I'd encourage you to provide a vent through the roof for the washing machine.

The operative language from the IPC is in 918.7: "Within each plumbing system, not less than one stack vent or vent stack shall extend outdoors to the open air." Looking at the definition of "plumbing system," I think that it includes your sewer pipes on the property, so you would have just one plumbing system, so AAVs only in the addition would be OK.

However, given my limited hands-on experience with AAVs, as well as uncertainty as to whether their performance will be impacted by how far away (pipe-run wise) they are from a vent open to atmosphere, I don't recommend the AAV only approach.

Is this referring to just a normal dry-vent going above the lav or for the AAV as well?

By "properly dry-vented lav" I meant either a vent through the roof or an AAV.

Cheers, Wayne

 

[DGZ]

Agreed -- I'm not 100% comfortable either with only using AAVs for the addition. Venting the WM through the roof is rather uncomplicated. Once in the attic I can run across the attic and tie into the existing vent stack on the far west side of the house. Or put a new roof penetration just for the WM closer to the east side of the house, but I prefer not adding another penetration through the roof (old roof with cedar shakes and 2 layer of shingles )

I've always planned to vent the WM through the roof. I just wasn't sure if I needed to get the bathroom group up there as well or if an AAV was sufficient for the group. Knowing that it is sufficient to wet vent the WC through the shower drain and wet vent the shower through the lav drain with an AAV is helpful in figuring out my final layout.

 

[DGZ]

Ok....so to confirm:

1. WM will be atmospherically vented. Drain will be 2" and insert downstream from bathroom group into 4" stack pipe.

-- Should the dry-vent above the san-tee continue as 2" or can I reduce to 1 1/2"?

2. WC 3" drain inserting into 4" stack pipe. WC wet-vented through shower and lav branch AAV.

3. Shower/lav branch will insert to the top of the 4" stack pipe. Shower drain will be 2" wet vented through lav drain and AVV. Lav drain downstream of AAV will be 2".

-- Is it necessary for the lav downpipe/trap/arm to be 2" or is it ok to be 1 1/2 in this setup?

4. How many cleanouts are overkill? Is it worth putting one on the WM drain and upstream of the lav drain as indicated in the diagram?

Based on the diagram below, anything else to consider?

 

[wwhitney]

1) The the dry vent for the laundry standpipe only needs to be 1-1/2".

3) Under the IPC, the lav san-tee can be 1-1/2" all around, i.e. the drain/wet vent only needs to be 1-1/2", and the dry vent only needs to be 1-1/2". Under the UPC (not applicable in NY state), it would need to be 2x2x1-1/2, so if you prefer you can do it that way. Or split the difference, use a 2x1-1/2x1-1/2 san-tee.

4) No opinion, although if the lav drain and trap arm are both 1-1/2", you could remove the lav trap in lieu of having a cleanout. You can also put a cleanout on the vertical lav drain/wet vent, rather than extending the horizontal portion.

Cheers, Wayne

 

[DGZ]

Sounds good. 1 1/2" lav trap and 2" drain/wet vent it is.

 

[Reach4]

1. I need an AAV on the lav trap arm because I have to route the drain through the floor due to being unable to vent directly into a dry vent through the roof.

You are saying you cannot run a vent pipe up inside the wall, and join the other vents in the attic. So an AAV would be the deal.

What is that 3-mountain-peaks symbol in your diagrams?

 

[DGZ]

What is that 3-mountain-peaks symbol in your diagrams?

Indicates what is above vs. below the floor. Below will be in crawl space.

 

[DGZ]

With this setup, is there any concern for gurgling through any of the traps when the WM discharges. A friend of mine mentioned this to me. He says the air pressure that is created when the WM discharges could push through the bathroom traps.

How much of a concern is this?