when to use 2x6 to allow for plumbing (interior walls)

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by ginahoy, Mar 10, 2014.

  1. ginahoy

    ginahoy New Member

    Messages:
    70
    Location:
    Sierra Vista, AZ
    As mechanical systems designer, I work with plans a lot. I often see 2x6 interior walls for plumbing but it's not consistent. I think architects and designers learn someone along the way to show 2x6 in certain situations but don't really understand when to apply, so they overdo this detail.

    In a single floor home, the only wall I imagine might need to be 2x6 would be behind a washing machine, to accommodate one of those recessed plastic drain panels. Even then I don't see why that wouldn't work with a 2x4 wall. In a two floor home, I can see how the primary drain from the upstairs fixtures would require a 2x6 wall on the lower floor. But I'm just guessing.

    Please elucidate me ;)
  2. Terry

    Terry Administrator Staff Member

    Messages:
    14,802
    Location:
    Bothell, Washington
    If you have a 3" waste line, 3.5" OD and larger than that for the hub of the fitting, then it's nice to place that in a 2x6 wall. It doesn't bend the drywall to fit around the fittings.
    If you are running 2.0" and 1.5" lines, then 2x4 is fine. A washer box fits in the 2x4 spacing.

    It's nice that exteriors are going 2x6 now. So many times with the older homes, the wall was pretty badly swiss cheesed getting the kitchen plumbing in.
  3. ginahoy

    ginahoy New Member

    Messages:
    70
    Location:
    Sierra Vista, AZ
    Thanks for quick reply. I advise clients to avoid any plumbing in exterior walls, but all of my clients are building high performance homes so 2x6 is pretty much standard. I guess my question is when would there ever be a 3" waste line in a wall on a single floor home? Shower, tub and toilet waste lines go down, not into the wall. Would a 3" drain line be required for a double vanity?
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,304
    Location:
    Cave Creek, Arizona
    The exteriors are going to 6" walls for increased insulation R value, they could care less about how the plumbing will be installed. SOme areas require a "full size" vent line all the way to the roof. In our area, meaning yours and mine, they require the aggregate areas of all the vent pipes to be the equal to the area of the incoming sewer pipe.
    Last edited: Mar 10, 2014
  5. Terry

    Terry Administrator Staff Member

    Messages:
    14,802
    Location:
    Bothell, Washington
    2" is used for a double vanity.

    Almost never with UPC. I don't think I've ever done on a single floor home. I need something like two 2" vents and a single 1.5" vent and I'm good. If things are spread out a bit, maybe more vents.
  6. ginahoy

    ginahoy New Member

    Messages:
    70
    Location:
    Sierra Vista, AZ
    Thanks for confirming what I suspected.

    In most cases I'm able to do a plan review well before ground breaking to ensure HVAC has been accommodated, and optimized when possible. I have also been advising clients to have a plumbing contractor review their plans, especially regarding DHW and hot water distribution. This will ensure a reasonable solution for waste lines and vents.
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,824
    Location:
    New England
    If someone wants a wall-hung toilet, you have more options if that wall is 2x6" construction.
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