DWV Remodeling help

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Vinnie Chenzo

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I have a remodeling project underway where the top of the 3" copper drain/waste pipe is corroded and has holes throughout and I intend to replace it with 3" PVC about 4' up the vent stack down to the waste stack where the copper goes to cast iron out to my septic. The home is 53 years old and I just bought it. I'm renovating the two bathrooms and found the issue once I ripped up some rotted subfloor... The worst of is was between the Bathroom #2 shower and toilet in the attached drawing.

I believe the design was working for all those years, but I gutted both bathrooms before moving in and really using them. I also didn't notice if the lavs had S or P traps before I ripped them out, but the lav drain pipes all come up thru the floor, not back thru the wall typical of P traps.

1. I might be able to get at least 3" (double 1.5") for the horizontal portion of a P-trap without going into the wall with piping. Drilling holes thru all my 2x4's seems like worse problem structurally on a support wall then using S traps if I had to! However, in Bathroom #1, if I use a P-trap do I then need to add dry venting at approx 42" (at least 6" above sink flood level) over thru a wall over to the vertical portion to the VTR stack and thus also bring the wet drain from those lavs across into the vertical part of the vent before it turns down horizontal through the floor, thus beginning the wet vent on the bottom of the vertical area, or can I keep it as is?

2. Should two lavs share a trap and/or drain pipe? In this case they are 32" apart on center. Not sure where they will be spaced in new vanity yet.

3. Is it ok to have the Bathroom #2 lavs branch in after the toilet? I can potentially have them drop down into the vertical portion of the stack as there might not be much room behind the toilet. I could possibly use a 90 with a side inlet. Not sure if the toilet could caus venting issues for these lavs? I can't easily pipe a vent up the wall and back across the attic to the main VTR stack either due to headers above what was a patio door and windows on that particular wall. Thru studs of two exterior walls to get back to the vent stack isn't an option either. AAV time possibly?

Thanks in advance,


  • bathroom wet vent design.pdf
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