Basement bath DWV check

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Phil P.

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Greetings! I've appreciated the great advice from folks here over the years and I'm back for a quick check on my basement bathroom DWV plan. First pic is floor plan and where I'd trench, and second is my attempt at an ISO drawing. I'm in Virginia under IPC btw and this is a permitted project that will be inspected.

I had to scratch my head a bit because the 4" main drain runs under the bathroom (fairly deep, like 14"). I want to use the lav as a wet vent for the whole bathroom group.

I really want to double check elevations/depths of pipes. Again the 4" is pretty deep, and my plan is to have 3" from toilet at that same depth with the 4x4x3 wye flat. Since the 2" from shower has to cross over the 4" main it will obviously be higher, and I'd put the 2" from lav at same height, again with the 2x2x2 wye flat. Where the 2" line ties in/drops down to the 3" I'd have the 3x3x2 wye turned up (over 45d right?) to vent the toilet too.

I believe the only length issue here is that the 2" line from shower has to meet lav/vent line in less than 8 feet, correct?

Does anyone see any problems, or is there a more logical/easier way to pipe it?

Thanks in advance and hope all have great 4th weekend. Philk
 

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wwhitney

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I don't have any under slab experience, but if you put a 3" street 45 into the branch inlet of a 4x4x3 wye, so that the inlets are parallel ("upright wye" configuration), they end up at about 6.5" c-t-c. So if you have enough room between the bottom of your slab and the 4" line, you have the option to do the bathroom group horizontal wet vent all at one elevation (well, 2% sloped). Then you can bring the branch drain parallel to the 4" line, 6.5" above it, or offset a little just by rolling the upright wye.

Not sure if that's better/worse than having your 4x4x3 wye horizontal, just wanted to mention the option.

Cheers, Wayne
 

John Gayewski

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I think you'd be better off coming off of the 3 directly for the shower. No reason to cross back over. Your iso is different than your plan view drawing on that way. I actually don't know why your crossing back over the 3".
 

wwhitney

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I actually don't know why your crossing back over the 3".
That was a result of the OP choosing that (a) the shower has to cross over the 4" main and (b) the 3" line from the WC should be at the same elevation as the 4" main (no drops, just 2% to a horizontal 4x4x3 wye). But while (a) is clearly necessary, (b) is not required.

Cheers, Wayne
 

John Gayewski

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That was a result of the OP choosing that (a) the shower has to cross over the 4" main and (b) the 3" line from the WC should be at the same elevation as the 4" main (no drops, just 2% to a horizontal 4x4x3 wye). But while (a) is clearly necessary, (b) is not required.

Cheers, Wayne
I don't see a reason to do it. Other than to avoid one vent. Which is worse than two. Unless the vent is terribly difficult to run for some reason no reason to make the plumbing worse.
 

Terry

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I think you'd be better off coming off of the 3 directly for the shower. No reason to cross back over. Your iso is different than your plan view drawing on that way. I actually don't know why your crossing back over the 3".
I agree, it's better to go straight to the shower with it's own vent.
The lav can come off the toilet vent on a trap arm.

lav_rough_1.jpg


The shower vent then connects to the toilet/lav vent at 42" above the floor.
 

John Gayewski

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I think sometimes people forget that the code is a minimum standard. It should be used to see what you can get away with in a situation where the best practice is not practical. Somehow this gets twisted into the code being too strict. The code is an engineering standard guaranteed to work in 99 percent of conditions which helpful. But it's still the minimum.

There is a balance between being over engineered and using the minimal requirements.
 

Jeff H Young

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I think sometimes people forget that the code is a minimum standard. It should be used to see what you can get away with in a situation where the best practice is not practical. Somehow this gets twisted into the code being too strict. The code is an engineering standard guaranteed to work in 99 percent of conditions which helpful. But it's still the minimum.

There is a balance between being over engineered and using the minimal requirements.
agree and this could be done wet vent off w/c you drill one maybe 2 studs on a petition wall
 

Phil P.

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thank you all for the feedback .. I've been back working on other parts of this project, but agree it's pretty easy to include a separate vent for the shower with the location of that wall. that's how I'll proceed. cheers!
 

bruzer29

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I don't have any under slab experience, but if you put a 3" street 45 into the branch inlet of a 4x4x3 wye, so that the inlets are parallel ("upright wye" configuration), they end up at about 6.5" c-t-c. So if you have enough room between the bottom of your slab and the 4" line, you have the option to do the bathroom group horizontal wet vent all at one elevation (well, 2% sloped). Then you can bring the branch drain parallel to the 4" line, 6.5" above it, or offset a little just by rolling the upright wye.

Not sure if that's better/worse than having your 4x4x3 wye horizontal, just wanted to mention the option.

Cheers, Wayne
My basement bath is very similar in that I have to tie into a 4" main(about 18" down!!). My bath group 3" main will be perpendicular to the 4" main. Can I do a long 90d from the 3" bath group main to get parallel with the 4" main then a 45d down to the 4x4x3 wye branch?
 

wwhitney

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My basement bath is very similar in that I have to tie into a 4" main(about 18" down!!). My bath group 3" main will be perpendicular to the 4" main. Can I do a long 90d from the 3" bath group main to get parallel with the 4" main then a 45d down to the 4x4x3 wye branch?
Sure.

If the two lines are truly perpendicular in plan (as seen from above), then you could omit the 45 and just roll your 90 so it's outlet is at 45 degrees from horizontal. That would hit your 4" line at a very specific point, so it would only work if that's a point where you can cut in the 4x4x3 wye.

Cheers, Wayne
 
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