Horizontal Washer Drain AFTER Standpipe 3 iinch??????

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Hammerlane, Oct 28, 2011.

  1. Hammerlane

    Hammerlane Member

    Oct 22, 2011
    I have another thread on here about how to plumb a washer and utility sink into an existing 4" stack. My plan was to run 2" horizontally to pick up the laundry sink and washer after tying into the stack.

    I talked with our local inspector here in Ohio and he said that any horizontal run to the stack after the washer standpipe has to be at least 3". He said the standpipe can be 2" but the horizontal run to the stack has to be at least 3"

    I checked into the Ohio Administrative Code » 4101:3 Board of Building Standards: Ohio Plumbing Code » Chapter 4101:3-4 Fittings and this is what it states for clothes washers:


    406.3 Waste connection. The waste from an automatic clothes washer shall discharge through an air break into a standpipe in accordance with Section 802.4 or into a laundry sink. The trap and fixture drain for an automatic clothes washer standpipe shall be a minimum of 2 inches (51 mm) in diameter. The automatic clothes washer fixture drain shall connect to a branch drain or drainage stack a minimum of 3 inches (76 mm) in diameter. Automatic clothes washers that discharge by gravity shall be permitted to drain to a waste receptor or an approved trench drain.

    So I wonder if running the 2" horizontally after the standpipe into the 4" stack will satisfy this code since the code says, "fixture drain shall connect to a branch drain or drainage stack a minimum of 3 inches (76 mm) in diameter."

    The "or" part gets me. Looks like you have to connect into a branch drain OR stack of at least 3". well I'll be connecting into a 4" stack. I can't imaging I would need 3" for the run to the stack. How do you interpret this?

    In the photo disreagrd the fittings they are not final yet. Just address the "green horizontal" run the will pick up the standpipe and sink then terminate into the stack.


    Attached Files:

    Last edited: Oct 28, 2011
  2. leejosepho

    leejosepho DIY scratch-pad engineer

    Nov 23, 2006
    disabled-retired industrial fabricator
    200 miles south of Little Rock
    Yes ...

    ... a branch drain ... a minimum of 3 inches (76 mm) in diameter.
    ... a ... stack a minimum of 3 inches (76 mm) in diameter.

    If the branch drain did not have to be 3", the text would likely convey something like this:

    ... either into a branch drain or into a stack, and then the stack would have to be at least 3".

    The poor wording in the code might seem ambiguous, but your inspector seems to understand what is meant.
    Last edited: Oct 28, 2011
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  4. nukeman

    nukeman Nuclear Engineer

    Nov 20, 2009
    Nuclear Engineer
    I can tell you how it is here (code for this is written like Ohio).

    In my case, I was able to do 2" standpipe, trap, and short run to stack. At the stack, I had 3" going down and 2" vent going up. No problem.

    What you have to look at is the definition of those terms:

    Fixture Drain: The drain from the trap of a fixture to a junction with any other pipe. (so from the trap to your wye used for the vent)

    Branch: Any part of the piping system except a riser, main or stack

    To me, you could go 2" up to your vent and will need to go 3" at/after that point.

    Yes, you will need the vent as the run looks too long otherwise (limit is typically 6'-8' for 2" pipe) and that stack is getting a dischange from above, so it couldn't be used as a vent anyway (if you were closer).

    Does that smaller line at the top of the stack drain anything from above? If so, you can't use it as a vent.

    However, what we think the code says doesn't matter. You can try to make a case for using 2" up to where you connect the vent, but all that matters is what the inspector thinks the code says. It is his job to interpret the code and enforce it. If he thinks you need 3" after the trap, then you'll need 3" after the trap (if you want to pass).
  5. Hammerlane

    Hammerlane Member

    Oct 22, 2011
    The 4" stack in the photo is servicing only 2 floor drains in my garage. You can see about 7 feet up on the stack where the 4" San-T ties in to pick up the floor drains. On top of this 4" San-T is a bushing for the 2". The 2" serves as a vent. This is the vent I was planning on tieing into for the laundry sink / washer standpipe set-up. No other fixtures in the house drain into this stack above where you see the San-T picking up the garage floor drains

    See updated photo.

    Attached Files:

  6. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona
    It is a question of semantics and interpretation. The code says "trap AND fixture drain shall be 2", but it does NOT specify what is meant by "fixture drain" or how far it can go before it has to be increased to 3". Normally, the washer drain "system" would be an integral package and then that package would connect to a 3" branch/riser drain. To this date, I have NEVER had to run 3" to a washer drain connection, but the washer drains DO eventually connect to a 3" or 4" drain line.

    As for #3, "is this vent needed" the answer would be yes, but you CANNOT connect it to the system at the ceiling where you show it, unless that point is 6" above the garage floor and the inspector approves it.
    Last edited: Oct 28, 2011
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