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Thread: Standpipe questions, venting and drain size

  1. #1
    DIY Junior Member DirtyBrad's Avatar
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    Default Standpipe questions, venting and drain size

    I'm installing a front-loading washer and dryer in a room in my basement which is adjacent to a full bath and I've got a couple of questions about venting and drain size.

    I'm installing a standpipe and washer outlet box. From what I've read, that standpipe and the drain back to the main should be 2". The problem is that the existing drain line is 1 1/2". When I tackle the bathroom, I will replace the whole run with 2", but that won't be until next year and I need to get the washer running in the meantime. Should I go with a 1 1/2" standpipe so the pipe is the same all the way back, or a 2" standpipe and reduce it? If so, where's the best place to do it? I have access to about a 6 foot horizontal run.

    The other big question is the venting. I've included a diagram which is hopefully pretty clear. The toilet and shower seem to be on a different line than the sink and standpipe. The main drain to the street is on the other side of the house. There's a horizontal pipe under the slab that runs over to that. I'm assuming the toilet, tub, and stack in the corner all feed down into that.

    The only fairly easy way I can think to add a vent close to the standpipe is what I have pictured in blue. Because of the window and a soffit on the wall, it's got to make the two bends. I'm also not sure if it's okay that it's running into the upstairs sink drain.

    The other thing I've thought of is using an AAV next to the washer. My understanding is that this has to be accessible, so I'd put it behind a panel or door or something.

    Any help or advice would be much appreciated.
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  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    Everything is wrong here.

    The toilet isn't vented,
    The lav isn't vented,
    The kitchen sink isn't vented,
    the Washer vent needs to be above the counter top of the kitchen sink by six inches.

  3. #3
    DIY Junior Member DirtyBrad's Avatar
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    Wonderful. You can't close with some positive news, like my picture is pretty or something?

    That bathroom is a non-priority now. It isn't used and won't really be until we go in and gut it, so I'm fine with that being a disaster. But I'm in the process of remodeling the kitchen, so I want that sink to be good. When you say it's not vented, is that because of the distance to the roof vent?

    I also want the washer working as soon as possible. If I hadn't just drywalled the whole kitchen, I'd do as you suggest and run the washer vent pipe up there and then over to the roof vent. What if I ran it up into the attic and then over to the roof vent there?

    What about the AAV next to the washer?

  4. #4
    Test, Don't Guess! cacher_chick's Avatar
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    Every trap must have a vent. The vents must run vertically upward until they are at least 6" above the flood rim of the highest fixture. New vents can be connected to the existing stack but only at a level above the highest drain connection. Sometimes it is easier to run more than one vent through the roof. If an AAV were allowed in your area, it would still not be sufficient for a washing machine drain.

  5. #5
    DIY Junior Member DirtyBrad's Avatar
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    Thank you both for the information. I look forward to hearing more.

    I'm curious as to why you say the AAV won't be sufficient for a washer. The specs on the valve say it's good for 6DFU, which seems like more than enough if I'm understanding things correctly.

    Here's what I came up with tonight for the drain. The standpipe and p-trap are 2" then reduced to 1 1/2". The AAV pipe is in 1 1/2" and the standpipe is 30" tall from the p-trap.

    Again, I'm aware this is out of code. I'm just trying to get the washer running reliably and this bathroom will be rarely used if ever. Once we redo it next spring, I'll either tie into the vent up in the attic or run another out of the roof as suggested and run 2" drain all the way back to the main stack.

    The washer is listed at pumping out 17gpm. To give a quick test, I dumped a 5-gallon bucket of water in as fast as I could, which wound up being about 15 seconds. I know the washer will put out a higher volume and that it'll be sudsy, but so far so good. No overflowing, nothing funny in the adjacent drains in the bathroom, and the trap was still fully wet.

    Tomorrow, I'll hook up the water and run a couple of loads at the heaviest setting with plenty of soap.
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    Master Plumber Redwood's Avatar
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    Quote Originally Posted by DirtyBrad View Post
    Wonderful. You can't close with some positive news, like my picture is pretty or something?
    Okay your picture is pretty...

    Now throw it in the garbage and draw a new one....

    The down side that I see is a sink overflowing with the washer draining...
    Could get pretty messy....

    How is the pitch on that washer drain?
    Looks backpitched...

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    Moderator & Master Plumber hj's Avatar
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    IF your drawing is accurate, then the new "vent" would not help the lavatory as the washer water flows past its connection, and your AAV does not help it either. AND, if that overhead line is "really" the sink drain, you cannot connect to it there. It would have to be behind the sink and at least 42 above the floor.

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    DIY Junior Member DirtyBrad's Avatar
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    Much appreciated.

    Just to be clear, the drawing isn't my proposed layout (except for my ill-advised vent idea). It's the existing bathroom that was tacked on by the previous owner of the house.

    The back pitch is just the picture. From left to right, the first three studs are all notched at 18" above the floor (floor is level). I cut the fourth one 1/8" higher.

  9. #9
    DIY Junior Member DirtyBrad's Avatar
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    Quote Originally Posted by hj View Post
    IF your drawing is accurate, then the new "vent" would not help the lavatory as the washer water flows past its connection, and your AAV does not help it either. AND, if that overhead line is "really" the sink drain, you cannot connect to it there. It would have to be behind the sink and at least 42 above the floor.
    I understand. As I said, this is a temporary step. Right now, I have no kitchen and no washing machine, so I really just need to get the washer functional and then get back to installing my kitchen floor and cabinets, so the house is livable. Next spring, I'll have the time and money to rip up this bathroom and get these problems fixed the right way. As I improve the house room by room, I'm researching and ahering to code. But if I jump immediately on every code violation I see, I'm going to get pulled in a million different directions and it'll be a year before I can get back to finishing my kitchen.

    In the meantime, you're saying my aav is protecting my standpipe trap, but that the washer water going past the bathroom sink and toilet might be pulling those traps dry?

    The overhead line is definitely really the sink drain. I removed the kitchen sink when I demoed the kitchen, and cut it off that line.

  10. #10

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    don't foget nail plates before installing your drywall.

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    DIY Junior Member DirtyBrad's Avatar
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    Definitely won't, thank you. I was a little horrified to see how mangled the studs where when I pulled the drywall off here (no nail plates on the existing stuff, of course), but at least they're just in there to finish the basement and not actually supporting anything.

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    DIY Junior Member DirtyBrad's Avatar
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    Terry, thank you. That's an excellent addition to my diagram and makes things very clear.

    Construction-wise, it would be a big deal to add the vent to the kitchen (upstairs) sink. It would actually be easier for me to link the basement venting up to the main vent in the attic or to run it separately out of the roof.

    I did some research on the codes. From what I've come up with, I'm under the 2006 NSPC for plumbing, which I believe states that a 1 1/2" drain doesn't need additional venting if it's closer than five feet to the stack. I was drawing this from memory and the kitchen sink is actually just under four feet from the main drain/vent.

    Am I correct then in assuming I will not be violating code by leaving just the existing drain connection from that sink? Again, 1 1/2" p-trap followed by a horizontal run of four feet, nothing anywhere above.

    Again, thank you for the help and the time correcting my crazy diagram.

  13. #13
    In the Trades Wally Hays's Avatar
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    Terry, under the 09 IPC that 2" lateral that the lav and washer dump into would have to be 3" where the lav ties in
    Perception is 3/4 of reality

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    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Also he's have to get rid of that flat dry vent feeding the toilet.

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