Double Vanity Back to Back DWV - Correct approach requested

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optimusgrime

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Greetings,

I have back to back bathroom vanities currently with one sink each. I am remodeling and this will become 2 sinks per bathroom.

I am attaching a graphic which has all the center to center dimensions referenced off of the current vent pipe.

Please let me know what the best approach is for this system. I am currently considering a SanT on the main vent, that has horizontal runners into a vertical SanT with additional Horizontal runners until the stub out is in line. This in my mind allows me to run a vertical vent tie in to the main existing vent.

IMG_5498.jpg


DoubleSinkBk2Bk.PNG
IMG_5481.jpg
 

wwhitney

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Is anything being wet vented downstream by the lav drain? If so, you need to show the full layout of both bathrooms. Also, how deep is the wall framing (2x4), and is the wall load bearing?

Some further comments:

- The central vent is not required.
- The horizontal drains don't need to be at the same height, so the center junction can be a quarter bend going into a san-tee, instead of a double san-tee.
- Double fixture fittings would be better at the left and right, but then you'd need to make the horizontal drains 2". Not sure if the double fixture fitting is required.
- Either way a cleanout below each the double san-tee/fixture fitting would be wise.
- An alternative approach that might be a bit busy would be to use 4 separate 1-1/2" san-tees.

Cheers, Wayne
 

optimusgrime

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Is anything being wet vented downstream by the lav drain? If so, you need to show the full layout of both bathrooms. Also, how deep is the wall framing (2x4), and is the wall load bearing?

Some further comments:

- The central vent is not required.
- The horizontal drains don't need to be at the same height, so the center junction can be a quarter bend going into a san-tee, instead of a double san-tee.
- Double fixture fittings would be better at the left and right, but then you'd need to make the horizontal drains 2". Not sure if the double fixture fitting is required.
- Either way a cleanout below each the double san-tee/fixture fitting would be wise.
- An alternative approach that might be a bit busy would be to use 4 separate 1-1/2" san-tees.

Cheers, Wayne
How about this? Also why is the center stack not needed, is it existing now and my plan is to tie back into it just to allow the system to have ease of equilibrium?


8D8566D5-649C-44B3-BF62-A186602016D0.jpeg
 

Jeff H Young

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Works good, its just not needed , its clean to run as shown to me and nothing at all wrong with it but the vent section in the middle is un needed and useless , probably takes less fittings though and Looks good if you like it I like it
 

wwhitney

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You didn't answer the question about what the drain with the lavs is doing downstream. If the current double lav drain is going on to wet vent more than one fixture, then at the point at which the wet vent starts to carry more than 4 DFU of drainage, the wet vent has to be upsized from 2" to 3". By adding 2 more DFU at the beginning, you would be shifting the point at which the wet vent exceeds 4 DFUs to just after the next fixture. In which case you would need to upsize some of the downstream drain from 2" to 3".

If the lavs drain is wet venting 0 or 1 fixtures, there's no issue.

Your last drawing is fine, as is your first drawing, just not optimized, IMO. The center vertical segment (between double san-tees) is not required, as it is not actually venting any fixtures. Each lav is being vented by the vertical connected to its san-tee.

And I still suggest offsetting the horizontal drains on the left and right, so they don't come to the common vertical drain at the same elevation. The "busy" option I mentioned would use the same pattern on the left as you used on the right. If I'm interpreting your rendering correctly, that would actually be one less stud penetration on the left.

Cheers, Wayne
 

Jeff H Young

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There is no reason to drill that stud Wayne that's just how he wants to build it. On his drawing one of the lavs is 16 inches from the stack the other is 21 the lavs are only offset by 5 inches . I'd just point the dff toward centers of lavs and be done with it not all those short pieces and 90s. a good idea to put a c/o as you said Wayne and perhaps at center stack (if accessible under drawers).
I wouldn't be worried in the least about the wet vent situation if 2 lavs was ok 4 will be too. If it was being inspected I'd consult with inspector , if it was a new build I would comply from the get go. I'm guessing most/ few inspectors wouldn't bring it up at all but there is always that chance and the code can be enforced
 

wwhitney

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There is no reason to drill that stud Wayne thats just how he wants to build it. On his drawing one of the lavs is 16 inches from the stack the other is 21 the lavs are only offset by 5 inches .
Not sure what you mean by the first sentence. On the rest of the above, apparently there happens to be a stud within that 5" spacing, per the rendering posted today.

Cheers, Wayne
 

Jeff H Young

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I like that too Wayne! I think he should just have back to back lavs off dff because they are so close the offset is only 5 inches but its personal preference .
I like the 1 1/2 piping though it saves structure !
 

John Gayewski

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Wayne's last mock up is better. I'm pretty sure a double tee isn't legal for the 4 lavs, and a double fixture fitting is just a it says double fixtures, this is 4 fixtures.

If anything use a double wye. You can run the vent through the center or just come with a street 90 and a cleanout.

The double fixture fitting IS required for UPC at the double fixtures.
 

Jeff H Young

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Wayne's last mock up is better. I'm pretty sure a double tee isn't legal for the 4 lavs, and a double fixture fitting is just a it says double fixtures, this is 4 fixtures.

If anything use a double wye. You can run the vent through the center or just come with a street 90 and a cleanout.

The double fixture fitting IS required for upc at the double fixtures.
Good point on the double fixture fitting. it could handle 2 showers so function not issue but ... but not certain on approved use . Now I find it be questionable for the side branches to be used as a drain rather than a trap arm.
Safer to use double wye
 
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