DWV design help.

[Mr.K]

Hello. I am new here and am looking for some help with this design. I will nee to plumb the laundry/utility sink and full bathroom (sink, shower, toilet. I’ve attached a sketch of the room for reference. Also, I have a done a rough layout of the system. Please help with the area outlined in white. Can I hook all the drains together at the bottom here on the right with a double sanitary tee? Thought, suggestions, ideas?

 

[wwhitney]

Since plumbing codes vary by state, we need to know which state in the PNW you are in. They all use the UPC, but Washington state has an amendment that would be useful in your situation.

If I'm following your drawing correctly, you are showing horizontal dry vents under the slab for the WC and possibly the tub. That's not allowed. The typical approach would be to use the dry-vented lav drain to wet vent the WC and the tub.

I'm not sure where you're proposing to use the double san-tee, but when joining drains on the horizontal, you need to use a wye or a combo (which is just a wye plus a street 45). Horizontal double combos aren't allowed, and horizontal double wyes should be avoided in favor of individual wyes.

If you clarify your location, I or someone here may be able to make a quick sketch of how to lay things out.

Cheers, Wayne

 

[Sponsor]

 

[Terry]

The lav could wet vent the tub and toilet. The washer washer and laundry tray has to come in downstream of that, as it can't be part of a wet vent system.
Using the lav as a wet vent for tub and toilet also eliminates the flat "unwashed" vent.
You can see have a cleanout in the wall.

 

[Mr.K]

Since plumbing codes vary by state, we need to know which state in the PNW you are in. They all use the UPC, but Washington state has an amendment that would be useful in your situation.

If I'm following your drawing correctly, you are showing horizontal dry vents under the slab for the WC and possibly the tub. That's not allowed. The typical approach would be to use the dry-vented lav drain to wet vent the WC and the tub.

I'm not sure where you're proposing to use the double san-tee, but when joining drains on the horizontal, you need to use a wye or a combo (which is just a wye plus a street 45). Horizontal double combos aren't allowed, and horizontal double wyes should be avoided in favor of individual wyes.

If you clarify your location, I or someone here may be able to make a quick sketch of how to lay things out.

Cheers, Wayne

Hi. I’m in WA.

 

[wwhitney]

Hi. I’m in WA.

So the diagram below should work. Red is 3", blue is 2", green is 1.5" (just the vents for the laundry sink and standpipe). Above the horizontal black line is the wall, and below it represents the slab, and there's a LT90 where each line crosses from the wall to under the slab. Circles are connections outside the wall/slab, and from left to right are: Toilet flange (with a combo below, not shown), lav trap arm stub out (at a san-tee, stub out should be green 1.5", rather the blue circle shown), and laundry sink (at a san-tee). The red line in the wall is the cleanout, termination details not shown. Likewise tub waste and overflow above the slab aren't shown.

Cheers, Wayne

 

[Mr.K]

The lav could wet vent the tub and toilet. The washer washer and laundry tray has to come in downstream of that, as it can't be part of a wet vent system.
Using the lav as a wet vent for tub and toilet also eliminates the flat "unwashed" vent.
You can see have a cleanout in the wall.

So the diagram below should work. Red is 3", blue is 2", green is 1.5" (just the vents for the laundry sink and standpipe). Above the horizontal black line is the wall, and below it represents the slab, and there's a LT90 where each line crosses from the wall to under the slab. Circles are connections outside the wall/slab, and from left to right are: Toilet flange (with a combo below, not shown), lav trap arm stub out (at a san-tee, stub out should be green 1.5", rather the blue circle shown), and laundry sink (at a san-tee). The red line in the wall is the cleanout, termination details not shown. Likewise tub waste and overflow above the slab aren't shown.

Cheers, Wayne

View attachment 85763

Thank you! I’m curious about this having two vents can I tie the two vents together up in the rafters for a single 2” roof exit?

 

[wwhitney]

Yes, vents can tie together anywhere that is 6" above the flood rims of all the associated fixtures. That's what I'm showing with the horizontal green line, the laundry standpipe vent tying back into the laundry sink vent. The same could occur between the laundry sink vent and the lav vent (which has to be at least 2" because it's wet venting the WC).

One question: is the above part of a house with other DWV and existing vents through the roof? There's a minimum requirement on the area of all the vents through the roof. The above drawing wouldn't meet the minimum if that's the whole DWV system, but should be fine as an add-on on an existing house with a compliant DWV system.

Cheers, Wayne

 

[Mr.K]

Yes, vents can tie together anywhere that is 6" above the flood rims of all the associated fixtures. That's what I'm showing with the horizontal green line, the laundry standpipe vent tying back into the laundry sink vent. The same could occur between the laundry sink vent and the lav vent (which has to be at least 2" because it's wet venting the WC).

One question: is the above part of a house with other DWV and existing vents through the roof? There's a minimum requirement on the area of all the vents through the roof. The above drawing wouldn't meet the minimum if that's the whole DWV system, but should be fine as an add-on on an existing house with a compliant DWV system.

Cheers, Wayne

So this is a stand alone utility facility. There is no more DWV system. In that case I would need both vents then?

 

[wwhitney]

Yes, in that case you'd want a 3" vent through the roof. So you could do something like below. Where the red circle in the wall is the cleanout, and I fixed the lav stub-out to be green (1.5").

The jog between the 3" stack in the wall and the 3" building drain in the slab is not necessary, it's just left over from the previous drawing. So you could route the 3" differently. The important part is the order in which things connect, and using the right fittings.

Cheers, Wayne

 

[John Gayewski]

Yes, in that case you'd want a 3" vent through the roof. So you could do something like below. Where the red circle in the wall is the cleanout, and I fixed the lav stub-out to be green (1.5").

The jog between the 3" stack in the wall and the 3" building drain in the slab is not necessary, it's just left over from the previous drawing. So you could route the 3" differently. The important part is the order in which things connect, and using the right fittings.

Cheers, Wayne

View attachment 85772

You have the toilet upstream of the tub trap arm. Does Washington permit this?

 

[wwhitney]

You have the toilet upstream of the tub trap arm. Does Washington permit this?

Yeah, Washington deleted the section in the UPC that would prohibit this arrangement. Why I asked about what state.

No 908.2.4 (edit: in Washington):

Chapter 9 Vents: Vents, 2018 Washington State Plumbing Code | UpCodes

UpCodes offers a consolidated resource of construction and building code grouped by jurisdiction

up.codes

Cheers, Wayne

 

[Terry]

I agree with a 3" vent through the roof. In Washington they want the same area through the roof as the waste line going out.
If you had other plumbing, then you could have gotten by with 2" with the addition of more venting to add up to a 3"
But like mentioned above, you just have the one vent for the building.

 

[Mr.K]

Yes, in that case you'd want a 3" vent through the roof. So you could do something like below. Where the red circle in the wall is the cleanout, and I fixed the lav stub-out to be green (1.5").

The jog between the 3" stack in the wall and the 3" building drain in the slab is not necessary, it's just left over from the previous drawing. So you could route the 3" differently. The important part is the order in which things connect, and using the right fittings.

Cheers, Wayne

View attachment 85772

Okay, great. This looks good. Is behind the toilet going up to the vent a 90 bend? If so, would two 45’s be required or recommended to transfer from the slab into the wall vent?

 

[Reach4]

No. The left green circle is the lavatory drain. Red circle would be cleanout I think, but maybe I got those backwards. No further venting of the toilet or tub needed.

Right green circle is laundry sink I think.

 

[wwhitney]

Reach4 got the details correct--the 3" in the wall is the combination 3" dry vent, lavatory drain, and wet vent for the WC and tub.

Where any drain turns from the wall to horizontal under the slab, a regular quarter bend is not allowed. You either need a long turn 90 (which in plastic just has about 1" more radius, IIRC), or two 45s. That applies to both the 3" and the 2" drains.

Cheers, Wayne

 

[Mr.K]

I’ve been reading through some of the other threads and came across this statement from another user, “With a wet vent from the sink, my understanding of the toilet NOT being the last fixture on the pipe requires the Double Wye/Symmetric Fitting.”
My question is with the referenced design, should I be installing a double wye 3x2x2x3 here for the tub and utility lit/laundry to connect down stream of the WC?

 

[wwhitney]

As per post #2 "horizontal double wyes should be avoided in favor of individual wyes."

The reason is that with individual wyes you can set the slopes of the branch inlets independently. While a double wye is a "flat" fitting, so at best the two inlets are level with each other, and they have 70.7% of the slope of the barrel. Or worse if one inlet is higher than the other, the lower inlet may have flat or reverse slope.

Cheers, Wayne

 

[Reach4]

I’ve been reading through some of the other threads and came across this statement from another user, “With a wet vent from the sink, my understanding of the toilet NOT being the last fixture on the pipe requires the Double Wye/Symmetric Fitting.”
My question is with the referenced design, should I be installing a double wye 3x2x2x3 here for the tub and utility lit/laundry to connect down stream of the WC?

1. While I don't fully understand the quoted statement, I am confident it is wrong.

Your red+blue+green lines look good. Why are you not content with that?

 

[Mr.K]

1. While I don't fully understand the quoted statement, I am confident it is wrong.

Your red+blue+green lines look good. Why are you not content with that?

It’s not that I’m not content at all. I just have one chance at this before I pour and wanted to ensure I wasn’t missing anything.

Things are coming along nicely with construction and should be ready to pour soon.
On question I have is regarding the clean out:
Can I move the clean out to the outside of the back of the foundation? That would mean that the WC would have a pipe running out back behind it and the clean out would pop up outside. Is this allowable?

 

[Reach4]

I am not a plumber, but I suspect it is very good. Having an outside cleanout would keep the machine outside. Any bends should be 45s or long sweeps.

I think when wet venting the toilet, a lot of people would feel better if your toilet waste joined in horizontally via a wye and maybe a 45, rather than from above. See Figure 1 on page 12 of https://wabo.memberclicks.net/assets/pdfs/Plumbing_Venting_Brochure_2018.pdf

Notice how the wet vented stuff comes in from the horizontal.