Need some UPC help on my rough in!

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MarkDevlinn

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Hi All,

Looking for some help on this So Cal UPC set up. I thought the one vent off the lav would be enough for the toilet and shower but a few people said I it won't work. If I wye off the toilet 3" and connect that vent to the lav vent would that suffice? From right to left in the picture is Shower, Toilet, Lav, then far left is laundry. All is currently 3 or 2 "

Rough.JPG
 

wwhitney

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So right now your drain connectivity pattern, starting upstream, is: laundry joins lav ; WC joins lav/laundry; shower joins lav/laundry/WC.

For wet venting both the shower and WC it needs to be: shower joins lav; WC joins lav/shower ; and laundry joins lav/shower/WC.

That's just the logical pattern of connections, not the physical left to right layout of the fixtures. So the laundry drain on the left just needs to stay separate until after the bathroom fixtures have all joined together.

And the shower, you'll need to reroute that drain, say, behind the WC to join the lav. For a 2" shower trap, you are also limited to 5' between the trap and the vent connection (the trap arm), and 2" of total fall. For wet venting, the vent connection is the connection between the lav and the shower.

So if the current place where you have the lav drain enter the slab would cause your shower trap arm to be over 5', you could move the lav drain in the wall, to move the slab entry point to reduce the shower trap arm to under 5'.

You also have the option to dry vent the WC and/or shower.

Cheers, Wayne
 

MarkDevlinn

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Thanks a lot for your response.... Trying the follow the best I can.... What would be the easiest way to resolve this current set up while keeping the WC, Shower, and Lav in the same locations? Dry vent via 2" the WC and Shower to horizontally in the wall to the Lav vent? Additionally, I am dealing with a very small clearance for pitch in this build which is making moving certain things around even more difficult. I have maybe 2" of clearance before I am at bottom of slab.
 

wwhitney

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And yes Landry will have its own independent wet vent.
That would be a dry vent, a vent carrying no drainage.

As for the simplest way to make it work, you could reroute the bathroom drains as in the diagram below (shower drain behind WC), if the red shower trap arm (from trap to the wye where the lav drain would join it) would be 5' or less. Also the WC drain, from the flange to the wye where it joins the green, needs to be 6' or less.

And for ease of drawing, I'm showing the green bathroom only branch drain as jogging at the exit, which keeping the laundry straight and without jogs. It would probably be better to do the opposite, so that the WC drainage path just has one 45 in it (via the wye where the shower/lav joins it).

Cheers, Wayne

Rough.JPG
 

John Gayewski

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What would be the easiest way to resolve this current set up while keeping the WC, Shower, and Lav in the same locations? Dry vent via 2" the WC and Shower to horizontally in the wall to the Lav vent
A dry vent needs to be verticle until your 6" above the toilet seat (for the toilet) and 6" above the curb (for the shower). You will need to find some walls and route the drains under those walls so your vents can stay vertical until above their rims.
 

wwhitney

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Or the following idea may be better, it would avoid any issue of the shower trap arm being too long.

It's hard to draw on the photo given its perspective. So for further advice, a photo from overhead, or a plan view drawing, would be easier to use.

Cheers, Wayne

Rough.JPG
 

MarkDevlinn

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A dry vent needs to be verticle until your 6" above the toilet seat (for the toilet) and 6" above the curb (for the shower). You will need to find some walls and route the drains under those walls so your vents can stay vertical until above their rims.
That shouldn't be a problem since this a one story with a loft with joists 8' above the ground floor.
 

MarkDevlinn

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Or the following idea may be better, it would avoid any issue of the shower trap arm being too long.

It's hard to draw on the photo given its perspective. So for further advice, a photo from overhead, or a plan view drawing, would be easier to use.

Cheers, Wayne

View attachment 85661
So I measured the current shower trap and its about 5' 2" from the start of the wye to the beginning of the trap (also an FYI, each WYE off the main 3" run has a 22 leading into it) which doesn't seem to meet code. The lav branch is exactly 5'6" square from the right side forms. So with that information the first diagram would work perfectly because the center of the shower drain is 18" off the right side of the interior wall (aka >5") The first diagram seems easier to solve my problem. One last quick question.... Is the shower trap arm measured from the beginning of the wye to the beginning of the p trap or from the 3" line to the end of the p trap?
 

wwhitney

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The shower trap arm is measured from the outlet of the p-trap (the point inside the trap where if you slowly added water to it, the water would first spill over out of the trap, aka the trap weir) to, for horizontal wet venting, the interior crotch of the wye fitting where the trap arm joins the wet venting drain.

I didn't quite follow your measurements, but if you come up with a new layout, go ahead and post a picture, preferably from a more overhead vantage point.

Cheers, Wayne
 

MarkDevlinn

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Hi Wayne, since I already have current layout and 3" fittings/ pipe are more expensive than 2", would a set up like this work?
 

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MarkDevlinn

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A dry vent needs to be verticle until your 6" above the toilet seat (for the toilet) and 6" above the curb (for the shower). You will need to find some walls and route the drains under those walls so your vents can stay vertical until above their rims.
That should not be a problem. Where the current lav protrudes out of the slab is dead center of the bathroom wall. So easy to make it 6" above toilet seat and curb.
 

wwhitney

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Absolutely, if you prefer to dry vent everything, that would work great; that was how it had to be done before wet venting was added to the UPC. As John says any horizontal dry vent (and any connection between vents) needs to be 6" above the flood rim level of any connected fixtures.

On vent sizes, all the individual fixture vents can be 1.5", except the WC, which needs to be 2". Also, the aggregate vent area through the roof needs to be at least the same area as the minimum building drain size. So if this is a standalone cottage or something, and the picture shows all the DWV, you need to have a 3" vent through the roof. Typically you'd make the WC vent 3".

What's going on with the double fixture fitting, is there another sink opposite the lavatory? What kind? All prior answers were based on just a lavatory, if you have a non bathroom sink there, it would preclude horizontal wet venting the shower and WC.

Cheers, Wayne
 

MarkDevlinn

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Great news!

Yes this is a stand alone Accessory Dwelling Unit (granny flat, guest house etc)

I think dry venting will be easiest then! I am going to protrude out of the slab all 2" and then cross the bridge of piecing it all together later in the build. Current objective is to simply pass my rough in. In other words, later on I can reduce to 1.5" for Lav and Shower and keep 2" for WC. I am slightly confused by "Also, the aggregate vent area through the roof needs to be at least the same area as the minimum building drain size." How would someone vent a 3" pipe out of a roof when wall framing is 2x4?

And yes the location of the current pipes are the wall dividing the kitchen and bathroom. So the side facing the WC is obviously the bathroom and other being kitchen. MY BAD for not disclosing. So with this information wet venting wouldn't work anyway which means moving to the above dry vent diagram is my only option?
 

John Gayewski

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Hi Wayne, since I already have current layout and 3" fittings/ pipe are more expensive than 2", would a set up like this work?
Just a suggestion. The shower vent might be in the way of the valve for the shower. If you roll that combo on a 45 and then correct it back to true verticle with a45 your still verticle and can be out of the way of the valve. There are actually a lot of ways to keep the vent from being in the way just keep it in mind.
 

wwhitney

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OK, given the kitchen sink, if you wanted to wet vent the shower and WC, you'd need to keep the kitchen sink and lav drains separate. The kitchen sink drain could join the laundry drain at the first opportunity, and then that combined kitchen/laundry drain would join the bathroom downstream of the bathroom.

However, that's all moot as it sounds like you want to go with dry venting everything. You will need to make the WC vent 3" through the roof. So the wall between the kitchen and bathroom needs to be a little bigger than a 2x4 wall--a 2x6 wall is plenty, but if you want to save 1.25" you can use a 2x4 wall and fir out one side of the framing with 1x2 or rips of 3/4" plywood. Simplest to do all of one side in one room, e.g. the bathroom.

As far as under slab plumbing, all the stub ups should be at least 2" anyway, the only one you would be oversize would be the shower vent stub up, but just keep that one 2" to the 3" WC vent stack.

Cheers, Wayne
 

wwhitney

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Actually, that "aggregate vent area through the roof" rule has an exception that may allow you to stick with just 2" in your ADU. See the following and figure out if it applies to you.


Cheers, Wayne

P.S. On the "required common building sewer", that will be 3" if your sewer lateral has 3 or fewer WCs across both buildings (house and ADU), or 4" if it has 4 or more. So if your house has (3) WCs and just one 3" vent stack through the roof (compliant), adding the 4th WC on the building sewer makes the minimum building sewer size 4", which requires 4" of area through the roof across both buildings. And 2^2 + 3^2 = 13 < 16 = 4^2, so a single 2" roof vent in the ADU would not be enough.

But if your house has 4 WCs and a 4" vent through the roof, or if it has only 1 or 2 WCs, or if it has more than the minimum vent area through the roof, then you may be OK with a 2" roof vent in the ADU
 

wwhitney

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PPS: I think CA just adopted the 2021 UPC, which changes the limit of 3 WCs on a 3" drain to 5 WCs, so the previous postscript needs to be changed accordingly.

 

MarkDevlinn

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Just a suggestion. The shower vent might be in the way of the valve for the shower. If you roll that combo on a 45 and then correct it back to true verticle with a45 your still verticle and can be out of the way of the valve. There are actually a lot of ways to keep the vent from being in the way just keep it in mind.
WOW I would have never thought of that and you would be correct in that it would be in the way! Much Much appreciate that suggestions!
 

MarkDevlinn

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Actually, that "aggregate vent area through the roof" rule has an exception that may allow you to stick with just 2" in your ADU. See the following and figure out if it applies to you.


Cheers, Wayne

P.S. On the "required common building sewer", that will be 3" if your sewer lateral has 3 or fewer WCs across both buildings (house and ADU), or 4" if it has 4 or more. So if your house has (3) WCs and just one 3" vent stack through the roof (compliant), adding the 4th WC on the building sewer makes the minimum building sewer size 4", which requires 4" of area through the roof across both buildings. And 2^2 + 3^2 = 13 < 16 = 4^2, so a single 2" roof vent in the ADU would not be enough.

But if your house has 4 WCs and a 4" vent through the roof, or if it has only 1 or 2 WCs, or if it has more than the minimum vent area through the roof, then you may be OK with a 2" roof vent in the ADU
Great information and it should not be a problem using 2" for the WC vent stack as the main house is only a 2br 1 bath with only 1 WC. So in total, the entire property currently only has 1 WC in the main house with the addition of 1 more WC in the ADU totaling 2 WC.
 
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