Can DWV vent be shared between shower and washer?

[James Borjas]

Hi all - longtime lurker but first time poster.

I am redoing my bathroom and trying to set up a plan for the DWV lines for a standing shower and stackable washer-dryer, which are side by side (30" wide each, with a 5" framed wall dividing them). I am unsure how to properly lay out the vent lines so that they work as intended and do not let gasses vent into the house or cause siphoning.

I've attached 2 potential layouts that I am considering. Ideally I would like to go with the simpler design where the drain from the shower and washer meet up under the floor in a 2 x 2 x 3" wye and then join together into the main drain, with a 2" vent running up from the center through the roof, but don't know if this achieves the goals of the vent lines or not.

I am looking for some feedback if either of them are correct/usable - criticisms and suggestions highly welcome! Thank you!

 

[Sylvan]

Picture #2 looks good to me

 

[Sponsor]

 

[James Borjas]

Picture #2 looks good to me

Thank you, I appreciate the feedback! If you don't mind, could you explain why picture 2 (with the extra vent lines) is a good setup whereas (I am assuming based on your response) that picture 1 is a bad setup, so I can understand the reasoning? Thank you!

 

[Sylvan]

By having individual vents as shown in picture 2 there is less chance of the traps siphoned out by negative pressure (back pressure)