Need advice on venting/plumbing a laundry room with sewage backing up

[vincatzero]

Hello.
I recently had a sewage backup into a bottom floor laundry room sink and washing machine. It led to me opening up the wall and realizing that the plumbing and venting of the room was wrong and needs to be redone.

This is a ground floor laundry room with a washing machine and utility sink. Directly above it is a bathroom with a tub, toilet and sink. There is a 3" PVC drain that comes down from the upstairs bathroom that the washer and lower sink were tied into. There was no venting at all.
I was planning on using the drain as a wet vent by running a vent line parallel with the washing machine drain line, but then I read that multi floor wet vents aren't allowed.

So I guess my question is, is there anyway to use the drain from upstairs as a vent? and if not, what are my options?

 

[vincatzero]

This is basically what my original plan was... am I correct that this isn't acceptable?

 

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[Reach4]

Your picture shows a too-short standpipe I think. It also has the arrow on the "waste leaves house" label upside down.

 

[Reach4]

Your picture shows a too-short standpipe I think. It also has the arrow on the "waste leaves house" label upside down.

A venting problem alone will not cause a backup.

You normally cannot use a drain from the floor above as a wet vent. If you are in an area that uses IPC, you could vent the standpipe with an AAV.

 

[vincatzero]

Yeah that picture was just a relatively close example of what my plan was. I just found it. I can see how that arrow was confusing. It was just to show the approximate height that the drain from upstairs 45s into a wall and goes outside.

 

[vincatzero]

I know it wasn't just a venting issue that caused the backup. The slope on the washer/sink drain was sloped backwards in a section. That's been corrected, now I'm just figuring out the vent.


So in no scenario is it acceptable to use the 3" drain line from upstairs as a wet vent?