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Thread: What to do about my main stack

  1. #1
    DIY Member Kimster's Avatar
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    Default What to do about my main stack

    So it turns out the collars on my stack stick out farther than the 2x4 construction in the room. As well, the stack was installed crooked so that the pipe, by the time it reaches the top plate also sticks out farther than the studs.



    Originally, I was going to get a section of it changed out to ABS because the sink installation I want is different than the original (I need the waste pipe higher because it's a wall-hung sink -- more like a tight install for pedestals). That would also take care of the collars. But now that I've noticed that the pipe also protrudes, what do I do?

    Do I get the plumber to increase the notch in the top plate and see if he can reposition the CI or do I get him to cut it above the plate in the attic as well as increasing the depth of the notch? Or can he install a smaller diameter pipe? Should I just change it out completely from just below the sink outlet through and out the roof?

    TIA


    ETA: Picture is not showing up. On the phone to my ISP -- hopefully will work later.
    Last edited by Kimster; 08-04-2010 at 08:31 AM.

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    It's easier it you attach the file.
    800 pixels or less, though I notice the picture you have is tiny anyway.

  3. #3
    DIY Member Kimster's Avatar
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    Here's the picture:

    Name:  stack.jpg
Views: 248
Size:  26.2 KB

    Because the walls were plaster on drywall lath, they punched through the drywall and thinned the coverage overtop of the pipe making it look like the wall was flat. It looks like the pipe is within the limits of the edge of the studs, but it isn't.

    Here's one of the whole thing:

    Name:  stackAll.jpg
Views: 240
Size:  21.0 KB
    Last edited by Kimster; 08-04-2010 at 09:13 AM.

  4. #4
    Nuclear Engineer nukeman's Avatar
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    If you don't replace the pipe, one option would be to fur the wall out a bit so the drywall/CBU will clear the stack.

  5. #5
    DIY Member Kimster's Avatar
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    Thanks nukeman. I was trying to avoid that because it's such a small bathroom to begin with. Then I'd be looking at the toilet being almost in the way of the undersized doorway and I'd have to get a custom sized shower pan.

    The plumber just left and he suggested cutting out about 8 feet of the CI stack (he said it was 2 inch -- I assume that's the inner diameter) and changing it out to 1.5 inch ABS for that length. It would have a sink emptying into it and nothing else above that. Then, in the attic, it would join back up with the 2 inch CI.

    What do you think of that plan? Would 2 inch ABS be thinner than the 2 inch CI that's there? Will there be enough air coming in? Not that I don't trust the plumber but I just want a second (or more) opinion.

  6. #6
    Nuclear Engineer nukeman's Avatar
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    A 2" PVC/ABS pipe is going to be about the same O.D. as the cast. However, the ABS/PVC won't have the hubs, so that'll save some space. As for dropping down to 1.5", it depends on what that line is venting more than just what the sink is draining into it. Might be hard to tell how everything is connected/vented, so it would be best to keep it at 2" if you can.

    How far does the stack stick out past the studs (give distance at the worst hub and just the pipe itself)?

    I have a similar situation in my small basement bath. They previously built a 2x4 wall in front of the stacks. I wanted to get every sq. in that I could, so I replaced it with a 2x6 wall and let most of the stack be between the studs (gained a couple inches of floor space). I still have one problem spot where there is a tee w/ cleanout on the base of a 4" stack. That sticks out past the 2x6 wall, but I will just fur out that little part and work it into the design. You could do something similar if you wanted (small bump-out on just the one stud bay). Your best bet would get the pipe to work with your installation, but a bump-out might be a solution if you can't get it to work.

  7. #7
    DIY Member Kimster's Avatar
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    Well, that stack is venting the toilet, sink and bath (soon to be shower) upstairs and a toilet, sink and shower directly below this bathroom. So what does that mean for the diameter required?

    I had thought about having a "bump" on that wall but the trouble is that it's going to be tiled and the tiles are 8x24 and will be installed horizontally. It would look really weird. Also, the toilet is just in front of that stack and I can't move it and I can't really have it out any further out into the floor space. Can anyone tell me how to calculate how big that vent stack should be for the number of fixtures on it? I also think I may have other vents because I see ABS pipe in the basement and one other going up into the attic, but there is only one that protrudes out the roof.

  8. #8
    Retired Defense Industry Engineer jadnashua's Avatar
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    CI is quite heavy. You may want to consider changing out everything above the point to ABS. If not, make sure that the pipe above is well supported, or you may have problems down the road with that heavy pipe on top of the plastic, which will bend. The inspector may not like it either.

    Would a second layer of drywall allow the wall to end up flat? Many toilets could stand 1/2" less between the tank and the wall, but each situation is different. IOW, how much does the thickest component stick out?

    Nohub connectors might be substituted for the hub on the CI to lessen the projection. Cut or snap the CI, and insert a small section of CI with nohub connectors at each end. The nohubs are only about 1/8-3/16" thick, so not much thicker than the pipe.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  9. #9
    DIY Member Kimster's Avatar
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    A second layer of drywall is out of the question because of space. In total, my walls can't be more than 1 1/8 inches thick including drywall, mud and tile. The drywall is 1/2 inch, tile, 3/8 and mud probably 1/4. Plumber is going to make sure the pipe is supported in the attic before he does anything.

  10. #10
    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Quote Originally Posted by Kimster View Post
    So it turns out the collars on my stack stick out farther than the 2x4 construction in the room. As well, the stack was installed crooked so that the pipe, by the time it reaches the top plate also sticks out farther than the studs.



    Originally, I was going to get a section of it changed out to ABS because the sink installation I want is different than the original (I need the waste pipe higher because it's a wall-hung sink -- more like a tight install for pedestals). That would also take care of the collars. But now that I've noticed that the pipe also protrudes, what do I do?

    Do I get the plumber to increase the notch in the top plate and see if he can reposition the CI or do I get him to cut it above the plate in the attic as well as increasing the depth of the notch? Or can he install a smaller diameter pipe? Should I just change it out completely from just below the sink outlet through and out the roof?

    TIA


    ETA: Picture is not showing up. On the phone to my ISP -- hopefully will work later.
    Hi,

    Cut the stack just above the floor so there is NO hub above the floor. Then YES cut it up the attic as well. and replace it ABS. Also just leave the line 2" regardless of what it is. You should beable to hide 2" inside a 2x4 stud with no insulation behind it. Make sure put a clean out in as well.

  11. #11
    DIY Member Kimster's Avatar
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    Thanks again, Doherty. I'll see if the 2" ABS will fit better and if it doesn't, I'll just notch out the top plate a little more. It doesn't have that far to go as is.

  12. #12
    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Quote Originally Posted by Kimster View Post
    Thanks again, Doherty. I'll see if the 2" ABS will fit better and if it doesn't, I'll just notch out the top plate a little more. It doesn't have that far to go as is.
    Notch the top plate anyway. While you have the piping removed it will take you 5 minutes to notch plate. Then you know it'll be perfect.

  13. #13
    DIY Member Kimster's Avatar
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    Doherty, are the CI pipes supported at the roofline as well as the attic plate, usually? I'm just wondering if he shouldn't go through the roof with the ABS instead of joining it back up with the CI up there. I guess that's a much bigger job? I have one of thoses outlets that are far larger than the pipe so that snow doesn't clog it because it only sticks up a few inches. I know I'll have to call a roofing company to put in a proper seal around it but that shouldn't be a problem. What do you think?

  14. #14
    DIY Member Kimster's Avatar
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    Hey, also, is it OK to cut CI in the attic with a reciprocating saw? Any chance of sparks that might burn the house down? Plumber isn't crazy about snap cutters -- says sometimes it crushes the pipe. Further to my last entry, he is going to cut the pipe where it turns into a 4 or 6 inch outlet at the roof and re-join it there. I know I sound paranoid, but this person said I don't need a permit and I know I'm supposed to have one for this work. I'm going to question him again about it before he comes back. I think it's just the speed and annoyance of getting permits that keeps people from pulling them. I suppose I could get one myself after the fact and say that we did the work ourselves with the help of a plumber and then get it inspected.

    No one in this town want to do this kind of plumbing. It's impossible to find someone that isn't too busy or doesn't charge stupid rates or doesn't want to sell you a complete bathroom with "their" fixtures.

  15. #15
    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Quote Originally Posted by Kimster View Post
    Doherty, are the CI pipes supported at the roofline as well as the attic plate, usually? I'm just wondering if he shouldn't go through the roof with the ABS instead of joining it back up with the CI up there. I guess that's a much bigger job? I have one of thoses outlets that are far larger than the pipe so that snow doesn't clog it because it only sticks up a few inches. I know I'll have to call a roofing company to put in a proper seal around it but that shouldn't be a problem. What do you think?
    The CI pipe should be supported quite well because it's heavy. Where they used hangers I don't know...

    If you're willing to spend the $ I would have the CI replace entiredly with ABS.

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