Shower drain and vent

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Mike58

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I am an owner builder and it is time to plumb the drains (actually, it has been time to do that for longer than I want to admit).

The idea is for the main drain (3") to run horizontally under the floor joists and through the foundation out to the septic tank. This means that for the shower, I have to run a vent horizontally under the floor to get to a wall to run up through the roof. My understanding is you are not supposed to run a vent horizontally until it gets up to about 4" above the flood level of the fixture it is venting. However, that seems like a good trick for a shower with a drain that is in the crawlspace of a ground floor.

The attached picture shows the layout and has my questions. I don't think distances are an issue, as no runs are more than about 3 feet. The main drain (3") has a cleanout at the far end, so the cleanout question is really just about whether the horizontal vent should have its own cleanout (which I would rather avoid, unless ...). The 2" verticle vent in the exterior wall will go up through the roof. Thanks for any help you can give me on this.
 

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Doherty Plumbing

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I am an owner builder and it is time to plumb the drains (actually, it has been time to do that for longer than I want to admit).

The idea is for the main drain (3") to run horizontally under the floor joists and through the foundation out to the septic tank. This means that for the shower, I have to run a vent horizontally under the floor to get to a wall to run up through the roof. My understanding is you are not supposed to run a vent horizontally until it gets up to about 4" above the flood level of the fixture it is venting. However, that seems like a good trick for a shower with a drain that is in the crawlspace of a ground floor.

The attached picture shows the layout and has my questions. I don't think distances are an issue, as no runs are more than about 3 feet. The main drain (3") has a cleanout at the far end, so the cleanout question is really just about whether the horizontal vent should have its own cleanout (which I would rather avoid, unless ...). The 2" verticle vent in the exterior wall will go up through the roof. Thanks for any help you can give me on this.

You can't have two fixtures share 1 trap like that and you can't run a flat dry vent like that either. You could wet vent the shower through the sink but you just need to reconfigure the piping so that the lav has a seperate drain and the trap-arm/fixture-drain of the shower ties into it via a wye.
 

Mike58

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Dohertyplumbing - Thank you for your help! It makes perfect sense now that you suggest it!

I can do what you say, as the lav is on the same exterior wall shown in the drawing (on our side of the shower), so I can run its vent up through the roof. A couple of questions. I assume that if I use the lav's drain as a wet vent for the shower, the lav's drain and vent up through the roof should all be 2". Is that correct? Also the wye you mentioned to connect the shower's drain to the lav's drain, can that wye be used on the horizontal plane, or should the shower's drain drop down into the lav's drain (if I have enough verticle room to do that)?

I seem to remember hearing it is a bad idea to use wyes and combos horizontally as they widen the waterway, causing it to lose velocity and drop out solids. Does that sound right to you?

Happy Holidays!
 

Doherty Plumbing

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Dohertyplumbing - Thank you for your help! It makes perfect sense now that you suggest it!

I can do what you say, as the lav is on the same exterior wall shown in the drawing (on our side of the shower), so I can run its vent up through the roof. A couple of questions. I assume that if I use the lav's drain as a wet vent for the shower, the lav's drain and vent up through the roof should all be 2". Is that correct? Also the wye you mentioned to connect the shower's drain to the lav's drain, can that wye be used on the horizontal plane, or should the shower's drain drop down into the lav's drain (if I have enough verticle room to do that)?

I seem to remember hearing it is a bad idea to use wyes and combos horizontally as they widen the waterway, causing it to lose velocity and drop out solids. Does that sound right to you?

Happy Holidays!

No you won't need 2" at all actually.

You could run 1.5" from the roof down to the connection of the tub. You are allowed to run 2 fixture units through a 1.5" wet vent not serving a water closet. A lav is only 1 fixture unit.

You can continue with 1.5" from the the shower to your next connection as well. You are allowed to drain 3 fixture units through a 1.5" branch and you're only draining 2.5 fixture units.

Ofcourse that is the minimum.
 

hj

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drain

There could be many ways to do it "legally" but that is not one of them, and the "best" way would depend on several factors we cannot see using your drawing.
 

Mike58

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hj, Tell me what you need to know and I will draw it better. I will experiment with Google Sketchup to see if I can draw it to scale.

Now is the time. Better to do it right now than have problems and have to tear it out later and do it again.
 

hj

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One thing would be a floor plan, with joist directions, showing the walls and location of the fixtures, and the location of the existing drains.
 

Mike58

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One thing would be a floor plan, with joist directions, showing the walls and location of the fixtures, and the location of the existing drains.

hj,

I put up a new post with drawings thinking this old post would be buried. But no reply yet to the new one. You can find it here https://terrylove.com/forums/showthread.php?34894-Plumbing-bathrooms-and-kitchen

Any suggestions will be appriciated.

This is new construction (though slow), so there are no "existing drains." However, roof vents are in place, so hopefully will not have to move, and some holes have been drilled through framing (which could be moved/redone if needed).
 
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