(206) 949-5683, Top Rated Plumber, Seattle
Results 1 to 12 of 12

Thread: Drain line in exterior wall?

  1. #1
    In the Trades mtcummins's Avatar
    Join Date
    Jun 2010
    Location
    Pittsburgh PA
    Posts
    380

    Default Drain line in exterior wall?

    Good evening/weekend all,

    I'm doing some remodeling that requires moving the drain line for a shower. There is almost no good way to do this, so what I'd like to do is kill 2 birds with one drain line and put it into a new furring wall on an exterior double brick wall, and then spray the furring space with spray foam. This way I can route my new pipe to the stack, and get some insulation value in the cold wall of the bathroom below it at the same time.

    The question is, can I run a 2" drain line with the fittings literally touching the brick of a double withe exterior brick wall without concern of freezing? I'm in Pittsburgh, PA, we get fairly cold winters here. I'll spray foam all the way around the pipe, but the side of the drain line will be essentially touching the brick and therefore not really protected by the foam. I have 3" absolute max to fur out, or I'll encroach within 15" off this wall to toilet flange, so there's no room to hold the drain off the wall. I plan to attach 2x3 (2 1/2" actual depth) studs to the brick and leave a channel for the drain line. With the variations in the brick surface, I should be able to just squeeze the fittings into that much space. I have enough vertical room that I can put a decent amount of fall in (an inch/foot shouldn't be a problem), to make sure that water moves through this section of pipe quickly and has no chance of water resting in the pipe. The run against the wall would be about 6-7 feet long, then drop into the 3" stack.

    The vent is fine in its current location, so not worried about it.

    Related to this, I'm assuming that I should use a 2" drain, as the shower has 2 shower heads... is this correct, or would 1.5" be sufficient? Last thing I want is any chance of a slow draining stand up shower, but the extra 1/2" would be helpful if the 2" pipe is not necessary...

    Thanks for your help guys!

    Mike

  2. #2
    DIY Senior Member dlarrivee's Avatar
    Join Date
    Jun 2009
    Location
    Canada
    Posts
    1,172

    Default

    Terrible idea.

    Insulation does not create heat.

    Having the pipe touching the brick and then spraying foam around the rest of the pipe will just help it to freeze.

    You need to route this drain elsewhere, there is no work around.

  3. #3
    In the Trades mtcummins's Avatar
    Join Date
    Jun 2010
    Location
    Pittsburgh PA
    Posts
    380

    Default

    Do you think it will get that cold in there? I would never put a water line in a wall like that, but a drain with decent slope, that will always have warm water running down it, seems like it might not be so bad. This surface is currently the wall of one of my bathrooms, and its not like I have the humid air condensing on the wall and freezing, so I'm not sure if the pipe would ever get cold enough to freeze even if it was standing water.

    Your point about putting insulation around the rest of the pipe possibly hurting more than helping is noted and a good point. I could leave the insulation just up to the pipe on both sides and behind it as far as it will go, but not covering the inside wall of it, so some of the room's heat would get to the inside of the pipe through the drywall... might help a little.

    As far as the local climate, most winters we get down into the low 20s with a few dips into the teens. Occasionally we'll have a day that drops below zero, but this is pretty rare and almost never lasts more than a night. Most assuredly, on those days the water doing down the drain will be piping hot

    Any other thoughts?

  4. #4
    Plumbing Contractor for 49 years johnjh2o1's Avatar
    Join Date
    Aug 2009
    Location
    South*East
    Posts
    1,121

    Default

    The line won't freeze. Unless the trap is exposed to cold temperatures. If the shower is vented the warm sewer gas moving through the line will prevent it from freezing. If this wasn't true what would prevent the line from the house to a septic tank from freezing? Most of these lines are not buried below the frost line in colder climates.

    John

  5. #5
    DIY Senior Member dlarrivee's Avatar
    Join Date
    Jun 2009
    Location
    Canada
    Posts
    1,172

    Default

    A perfectly healthy drain will not freeze. One with a little crud in it might.


    It is just bad practice, you can justify it all you want, but I wouldn't do it in my own home.

  6. #6
    In the Trades Gary Swart's Avatar
    Join Date
    Sep 2004
    Location
    Yakima WA
    Posts
    7,246

    Default

    Freezing drains is not a problem except perhaps in the Far North with temperature below zero for weeks on end. As already mentioned, don't insulate between the interior wall and pipe as insulation does not heat anything, it only slows heat transfer. An insulated vacuum bottle does not heat your coffee, it will only keep it hot longer than a non insulated container because the insulation slows the heat of the hot coffee from being lost. Insulation will not warm the house or cool it, it just slows heat loss in the winter and slow heat entering the house in the hot summer.

  7. #7
    In the Trades mtcummins's Avatar
    Join Date
    Jun 2010
    Location
    Pittsburgh PA
    Posts
    380

    Default

    Thanks everyone for your input. I tend to think it would be fine in this situation. I imagine that up in Canada it would be more concerning, as the winters are generally much more brutal than here. The extra fall on the line should keep water moving through it fast enough to prevent any crud build-up. If there's a lot of crud in my shower drain line, I have bigger problems to worry about (my personal hygiene) than a potentially freezing drain anyway... gross.

    Even if it did manage to freeze up a tiny bit (not sure how it would, but if it did), the hot water from a shower would melt through it quick. The trap will be 3 feet away from the cold wall, in a heated/insulated floor (my whole house is radiant floor heated), so no chance of the trap ever getting cold. And it is vented properly.

    Any thoughts about 1.5" vs 2" line for this 2 shower head setup? I guess you have a potential load of 5 GPM. I don't remember the fixture units for this setup off hand... would it be a bad idea to run this through a 1.5" drain? I def don't want to skimp there, but if its a perfectly acceptable load on a 1.5", it would make it a lot easier to get it through there, and I could keep the pipe from touching the outside wall.

    Thanks,
    -mc-

  8. #8
    DIY Senior Member dlarrivee's Avatar
    Join Date
    Jun 2009
    Location
    Canada
    Posts
    1,172

    Default

    2", if you must.

  9. #9
    Test, Don't Guess! cacher_chick's Avatar
    Join Date
    Jan 2008
    Location
    Land of Cheese
    Posts
    3,147

    Default

    2" is the minimum (and common) drain size for a shower in the U.S.A.

  10. #10
    In the Trades mtcummins's Avatar
    Join Date
    Jun 2010
    Location
    Pittsburgh PA
    Posts
    380

    Default

    Hmm, 2" is minimum? My plumber originally plumbed this with 1.5" and it passed inspection (it was only a single shower at that point). Pittsburgh tends to be really over-zealous on code stuff (we have to have 2 traps and 2 vents on a double bowl kitchen sink, for one stupid example), so I'd be surprised if they'd let something like that fly.

    That said, I generally plumb all of my tubs and showers 2" when I can fit the pipe anyway, just to be safe. I'll only put one lav into a 1.5, if there's two I'll bump it up to 2" where they join. Might as well do it a tad overkill if its feasible.

    Ok, so I'll def go with 2" for this. I looked at it again today, and I have a little more than 18" to my toilet flange, so I'll prolly try to get another half inch to an inch of furring in there, and get a good 1/2" - 3/4" gap between the cold wall and the pipe which i can spray foam behind. That will give me between R3.5 and R5 to help keep the cold away from the pipe, and the bathroom heat through the drywall to the uninsulated inside wall of the pipe should def keep this line above freezing no matter how cold it is outside. It will be up near the ceiling where the room is warmest, so I really don't think there will be any problems.

    Thanks all, for your input. Have a great weekend!

  11. #11
    Test, Don't Guess! cacher_chick's Avatar
    Join Date
    Jan 2008
    Location
    Land of Cheese
    Posts
    3,147

    Default

    Once past the vent take-off, the pitch can be increased to ensure that the pipe drains quickly as the years go by.

  12. #12
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,405

    Default

    Long ago, in the USA, they allowed 1.5" drains for showers, but that hasn't been true for a long time (it's still allowed in Canada from what I hear). It might be grandfathered under certain circumstances, but never for new or tearout remodels. Now, the vent might work at the smaller size, but that depends on the fixture units.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

Similar Threads

  1. Can I secure a gas line to an exterior wall?
    By Ian Gills in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 8
    Last Post: 07-16-2010, 10:33 AM
  2. New Vanity: Distance from drain to wall and does drain need to line up?
    By sanrico in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 6
    Last Post: 11-30-2009, 04:46 AM
  3. 3" or 4" PVC for Sump Discharge Exterior Drain Line?
    By dwt in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 1
    Last Post: 07-13-2009, 07:17 AM
  4. PEX in an exterior wall
    By Noth Jersey in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 11
    Last Post: 01-27-2009, 06:43 PM
  5. water line on exterior wall
    By tameria11 in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 4
    Last Post: 02-19-2008, 04:15 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •