Adding laundry standpipe next to soil/waste stack

[cmwand]

I'm about to start a laundry room remodel on my house's first floor and would like to move the washer and dryer. The location the washer would be moved to is on a wall that has a 3" waste stack servicing one (and only one) bathroom ( with a tub, toilet and sink) on the second floor above the laundry room. The trap arm for the new washer standpipe would be about 4-6" inches to the existing waste stack (so it's close to the minimum trap arm length).

My question is: Am I allowed to use the 3" waste stack as a wet vent for the new washer standpipe so I can avoid putting in a new dry vent? I don't have a good way to run a dry vent up to the roof from the new washer location. I think/hope the answer is yes because the trap arm isn't long enough to require a dry vent and the waste stack is large enough to not cause siphoning, but I confess I don't know the finer points of wet venting, such as same floor/different floor limitations, etc.

Thanks in advance for any advice y'all can give!

Chris

 

[Terry]

The washer needs it's own vent.
Wet venting is only for same floor fixtures, bathroom only. The washer doesn't get included in that.

 

[Sponsor]

 

[cmwand]

The washer needs it's own vent.
Wet venting is only for same floor fixtures, bathroom only. The washer doesn't get included in that.

Not the answer that I wanted to hear, but thanks for setting me straight.

That brings me to my next question: How do you feel about my using an AAV/Studor valve to vent the washer drain? Putting in a dry vent would require a good bit of demo and drywall repair. I'll have some deep cabinets above the washer so I'd probably just stub out the vent pipe and put the AAV in the cabinet where it's easily accessed.

Thanks,
Chris

 

[cmwand]

Okay, I've done a little more digging and come up with an alternative to an AAV. I'm familiar with island vent loops and could do something similar to vent the washer standpipe and want to make sure that's kosher. Effectively, I'd have the washer standpipe drain into the existing 3" waste stack in the wall behind the washer that comes down from the second floor bathroom above. Then I'd run a vent loop up above the top of the standpipe height and back down into the unfinished basement below the washer where I'd tie into the 2" vent pipe for the bathroom that is adjacent to the unfinished basement underneath the washer.

I've attached a diagram to help explain. I've simplified the layout of the vent pipe down in the basement, but I would make sure that I have accessible cleanouts and proper pitch/flow and fittings to the existing vent pipe (so no water can get trapped in it). Everything within the red dashed circle is new; everything outside is existing.

Is this acceptable? I know that most folks here are against AAVs except as a last resort, so I wanted to see if this would work.

BTW, I know my picture shows the existing 2" vent pipe in close proximity to the washer standpipe, but in reality it's not practical to tie into it on the 1st floor as the picture would lead you to believe. To run a new vent section to the existing vent I'd have to tear out a bunch of ceiling drywall, drill through a bunch of floor joists and tear into a soffit and wall to get to the existing vent pipe.

Thanks again in advance for any advice!

Chris

 

[Reach4]

put the AAV in the cabinet where it's easily accessed.

That AAV works unless local rules say otherwise. You probably should have a small vent panel in the cabinet, but I doubt that the cabinet would be sealed enough to cause a problem if you did not actually do that. I don't know if your island vent is allowed for this purpose or not.

 

[cmwand]

Okay, thanks for the quick response. I saw some responses in other threads here suggesting that AAVs weren't allowed by some codes or, even if allowed, aren't ideal for pump discharge like on a washer due to the fact that the sudden high volume of water creates back pressure in the rest of the pipe and an AAV, unlike a regular vent, doesn't allow the pressurized air to escape. I suppose the reality of my layout would allow much, if not all, of that back pressure to escape up the 3" waste stack which will be very close to the drain standpipe, but since the existing waste stack can't be used as a wet vent, I don't know if it's kosher to even think along those lines.

Does anyone want to comment on whether the island loop vent would be allowed for this purpose and if that's better than the AAV?

An AAV would certainly be easier to install, but my primary concern is getting this right and making it work over the long run.

Thanks!

 

[hj]

The back pressure the AAV cannot handle is caused by the slug of water coming down the stack from the upper bathroom.

 

[Asktom]

Tie into the 3 stack with a 3x2 san tee, the 2 branch centered 12" above finish floor. Use a 2" trap and a 30" standpipe. Between the stack and the trap put a 2x1 1/2 combo (2" also OK), go up to a point at least 6" above the top of the standpipe, add an elbow and with a slight uphill grade go to the existing basement vent. Tie into that vent with a san tee turned upside down so the sweep is toward the roof.

 

[cmwand]

Thanks Asktom. Unfortunately, while my simplistic drawing shows the existing basement vent pipe in the same wall as the 3" waste stack, in reality, it's on the other side of the room. To get the new vent connection from the standpipe to the existing basement vent pipe, I'd have to tear out the drywall ceiling, drill through a bunch of ceiling joists, tear out an existing soffit, and tie into the existing vent pipe above the ceiling. Which is exactly what I was hoping to avoid by using an AAV or vent loop to connect the vent under the floor.

So, final try--anyone willing to opine on whether the AAV or loop vent are reasonably acceptable?

Thanks in advance,
Chris