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Discussion Starter #1
Currently trying to plumb a drain from a freestanding (with legs) bath vanity down into the crawlspace and onward to the waste/vent, 5' away. Problem is that the vanity will be located on an 2x4 exterior wall. The wall/floor plate is also on the concrete foundation with the rim joist still a few inches inside the envelope. So, I won't be able to drill down through the plate for the 2" drain, and any void under the floor starts at about 2" inside the room.

Apparently, I cannot use an s-trap to go straight down through the floor, but instead have to use a p-trap into the wall!

What's the best way to plumb this vanity if it cannot go hidden into the wall then downstairs via through the plate?

This is a corner room with 2 exterior walls at right angles to one another.
 

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Do you know about how high the legs are going to be? Could you just bring the drain forward a couple inches to avoid the slab and not have it be an eyesore? If you can move it far enough away from the wall and not have it be visible I would probably go that route.
 

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I would just build another 2 X 4 wall right in front of that one.
That way the drain and the supply lines will never freeze and still be able to be run behind the new sheetrock.
Simple enough to add jamb extentions to the window.
I also would insulate that new wall, in your area I'd bet if this was new constrution they would have made you use a 2 X 6 wall so R-19 could fit.
(that window my be right were you would install a mirrror or medicine chest, may need to get rid of it)
 

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Discussion Starter #4
Thanks for your input :wink:

fetzer85 -- that might just work out. I'll know for sure after the vanity arrives when I can measure it properly. I guess I'll also have to run the supply up through the floor, perhaps along with the drain.

joecaption -- we thought of that but space is a real premium in this ensuite and so we need all the depth of room we can get. Btw, the old leaky window is being removed as the room is now well lit by a shared 4x4 skylight over the shower (just out of camera range to the left).

Incidentally, what is the reasoning behind the Code getting rid of s-traps? Seems they were used all over and would have been especially appealing in my situation ..and wouldn't a p-trap in this instance be similar to a large s-trap: go into the wall, then comes out right away??
 

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Incidentally, what is the reasoning behind the Code getting rid of s-traps? Seems they were used all over and would have been especially appealing in my situation ..and wouldn't a p-trap in this instance be similar to a large s-trap: go into the wall, then comes out right away??
I believe they were prone to siphoning out the water in the trap, letting sewer gasses come back up through the sink. The horizontal run of a P-trap breaks the siphon so it can't suck the water out of the trap.

I would conjecture that a P-trap followed by a horizontal run of 12" before going down into the crawl would be a workable solution, although I have absolutely no idea if it would be allowed by code.
 

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S traps do not have vents. Vents keep a trap from siphoning. I assume you will be venting that trap.
 
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Discussion Starter #7
S traps do not have vents. Vents keep a trap from siphoning. I assume you will be venting that trap.

Yes. Once the 2" drain is down into the crawlspace the distance from the trap will be around the max of 5' to the waste/vent stack ..which comes up through an interior wall on the opposite side of the ensuite (approximately where the camera was) to the attic directly above. Hmm, so in this case an s-trap would then be classified as vented?
 

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Yes. Once the 2" drain is down into the crawlspace the distance from the trap will be around the max of 5' to the waste/vent stack ..which comes up through an interior wall on the opposite side of the ensuite (approximately where the camera was) to the attic directly above. Hmm, so in this case an s-trap would then be classified as vented?
I doubt that will work. The vent has to be right at the point the water turns to go down into the crawl in order to break the siphon.

I'm no plumber, but would an AAV help in this case?
 
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