Add Sink to Laundry DWV

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Sheenbean

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Hello all,

Hope everyone is doing well!

I need some advice. I am in southern California, Orange County. I am adding a laundry room inside the house just on the other side of the garage wall where it is now. I would like to put the plumbing in the wall using a laundry box and on the garage side, where the washer used to be, a utility sink.

Current wall is 2x4, vent is 2" cast iron pipe.

Inside wall of pending laundry room

sean-Laundry-Room-Wall.jpg


Current DWV in garage

sean-Garage-Wall-Current.jpg


My question is, to meet code, do I have to build what is shown here below, with sink drain on other side of wall or can I stack the sink drain over the laundry drain in the existing vent? I believe that would be called a wet vent?

washer_rough_b.jpg


If this is the only option, a 2" pipe (2 3/8 OD) through the 2x4 exceeds what's allowed, can I use a shoe stud or is there another option?


EDIT:
I don't know how I missed all the other posts for similar topic. Is this image below an option for me and any drawbacks?

index.php


Thanks!
Sean
 
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wwhitney

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In re the 2x4 studs, you could drill one for a central 2-1/2" hole and repair it with a Simpson HSS2-SDS1.5 stud shoe.

Whether you have to do that doesn't depend on whether you can stack the san-tees, it depends on your open stud bay width. A 2" solvent weld-p-trap is 6-7/8" from center of inlet to trap weir; the minimum trap arm is length is 4" (2 * 2"), measured to the inside face of the vertical vent; and the center-line of the vent is 1" further, for 11-7/8" minimum center to center. With the 2-3/8" OD, that's 14-1/4" edge of pipe to edge of pipe, and then the hubs on the fittings are wider. So it certainly won't fit in a 14" stud bay (16" o.c. with old 2" thick studs) and probably won't fit in a 14-1/2" stud bay (modern 1.5" thick studs). [Edit: if you wanted to fur out the wall to 5" of depth, you could swing the trap u-bend around so that the standpipe runs past the trap arm, then it would fit.]

As for stacking the san-tees, a laundry sink (2 DFUs) is allowed to be over a washer standpipe (3 DFUs) in a vertical wet vent (but not vice versa), but you can't do it with a 2" drain. The vertical wet vent between the two san tees needs to be at least one pipe size bigger than both the minimum drain size of the upper fixture and the minimum vent size of the lower fixture. And the minimum drain size of a laundry sink is 2" (starting at the san-tee), so you'd need at least a 2-1/2" drain (an odd size, 3" in practice). https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/9/vents#908.1.1

So doing something like in your last picture is likely the way to go. Another option is to use two san-tees side by side, with the drains combining below, and the vents combining above (at least 6" above both flood rims), using a wye and 45.

Cheers, Wayne
 

Sheenbean

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Thanks for the response and the information, I really appreciate it.

If I understand correctly, put wye with 45 at the bottom (near floor) to create 2 branches for each and then reattach at the top at least 6" in over flood plain.

That may be tight and staying in the 6" to 18" for the laundry p-trap height. I forgot to mention garage is 5" below house slab level. Is this a better option from a drain capacity standpoint? I think I can make it happen, just need to work it out.

Again, really appreciate your time. Have a good one!
 

wwhitney

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No opinion on which layout is better, use whatever fits.

A slight variation on the picture you posted would be to use the following fittings going up from the slab: A wye with entries vertical and diagonal, straight entry gets the san-tee for sink, diagonal entry gets a (possibly street) wye with entries diagonal and horizontal, diagonal is the standpipe vent and gets a 45 to go vertical; horizontal gets the laundry standpipe trap arm.

Anyway, just some options, I don't mean to confuse the situation.

Cheers, Wayne
 
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