I'll probably get beat up about this (I know nobody likes a studor vent), but here goes:

Washing machine recently began "sudsing" up the standpipe.

Probably due to the fact that water softener is now installed.

Anyway, I took apart the drywall and found:
a) the standpipe was only 12" (I'm measure height from P-trap to top of standpipe)
b) There doesn't appear to be a vent anywhere close by (some of the walls in the basement I cannot access, but I don't see a vent for at least 12' along the run)

Sooooo, I read the standpipe should be 18" min. and a max of 30"

So I made it 18" and it SEEMED okay, but it still "overflowed" a little. (ironically only when a certain someone does laundry--not me)

So then I thought maybe the venting wasn't done right, so I thought it would be easier to try a studor vent to see if it alleviates the problem before I go cutting a hole in the roof.

But then I saw on some other forums that a "long" standpipe will cause excess sudsing???

If I do go with a studor, I'm assuming I can place it "downstream" from the P-trap (it would be within 2' of the P-trap)?

How "tall" should I make the standpipe for the studor vent?

The only reason you have a sudsing problem now is because you are using too much detergent.


Having a water softener greatly reduces the amount of detergent needed to clean clothes.


Figure out trial by error what is the correct amount needed to clean your clothes. At that point I bet your sudsing problem will disappear.

I believe that our code, (NYS/IPC) does not permit AAV's to be installed on any fixture that utilizes a pump to discharge waste water. I would suggest raising the stand pipe to 30" and having the drain line snaked and cleaned. If there isn't an atmospheric vent you may need to install one, call the local Inspector.

e-plumber

Thanks for the suggestions.

I'll try the soap suggestion first, since it's the easiest.

If NYS truly follows IPC, then I can vent the line out through the sidewall of the house (running a vent line up through the roof will require tearing out an entire ceiling of drywall, plus two floors of drywall to get to the roof)

I had a similar problem. In my house, there were two atmospheric vents(auxillary, not main) that went to the roof but when they extended the kitchen, they had to be removed so they combined them into one vent and attached a studor.

I was getting suds that was flowing out. I tried the soap thing and it worked fine.

Rocky