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Thread: Long HORIZONTAL runs on the main stack?

  1. #1
    DIY Member Gordan's Avatar
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    Default Long HORIZONTAL runs on the main stack?

    Hello, all!

    I'm embarking on a remodel of three bathrooms in a terrible condition, in a 50s house in Southeastern PA.

    Bathroom 1: first floor; one shower, one sink and one toilet. No venting anywhere; in fact, it would appear that the sink somehow drains into the shower drain, which in turn drains into the main stack, as there is no separate drain for the sink in evidence. I haven't demolished this yet.

    Bathroom 2: second floor; one shower, one sink and one toilet. All fixtures have separate drains into the main stack. None of them are vented.

    Bathroom 3: second floor; one tub, one sink and one toilet. All fixtures have separate drains into the main stack. None of them are vented.

    The main stack itself discharges horizontally. In fact, the only vertical part of it is the drop from the second floor to the first floor. It is correctly sloped. It is 3" hub-and-spigot cast iron. It's laid out as follows, going downstream:

    A) From the vertical roof penetration, it drops between rafters (about 45 degrees) into Bathroom 3. It then turns vertical again for four feet before turning horizontal. This is a sweeping combination of 45 degree elbows.

    B) The three fixtures in Bathroom 3 enter the main with wyes: first the toilet, then the tub, then the sink. The main is still horizontal at this point.

    C) The three fixtures in Bathroom 2 enter the main with wyes: first the shower, then the sink, then the toilet. The main is still horizontal at this point.

    D) After the total horizontal run of about 15 feet, the main drops vertically for about 10 feet into the basement. It again turns horizontal and there is a cleanout at that point.

    E) The fixtures in Bathroom 1 enter the main with wyes: first the toilet, then the shower (and presumably sink.) The main is still horizontal at this point, and it continues horizontally for a further 15 feet.

    F) The main drops vertically about 18", turns horizontal again (there is a cleanout at this point) and then promptly exits the building underground.

    Everything I read and see seems to suggest that the main stack ought to be vertical and only branch drains are allowed to be horizontal. Is that true, and if so, what am I supposed to do with the situation in which I find myself? The issue is not fixture vents, as I'm committed to add those, or any other fixture plumbing details, but the main itself.

    Many thanks in advance for your advice,

    Gordan

  2. #2
    DIY Member Gordan's Avatar
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    Oops, a correction: just before the toilet in Bathroom 2 joins the main, it drops down slightly out of the joists and into a soffit and then makes a 90 degree turn in the horizontal plane.

  3. #3
    Forum Admin, Expert Plumber Terry's Avatar
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    Whether the main waste line is vertical or horizontal isn't so much the issue, but where the venting is placed to break up the siphon effect when waster is running by the wyes or tees.
    Place a vent between a p-trap and the next connection does that.

  4. #4
    Moderator & Master Plumber hj's Avatar
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    You give a lot of information, but most of it is useless as to how to do the replacement. The main can go in any direction it has to, as long as it is going downward, and where the branches connect is immaterial. What makes you think you are qualified to do a job this extensive?
    Licensed residential and commercial plumber

  5. #5
    DIY Member Gordan's Avatar
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    Wrote a reply and it disappeared. Quick recap:


    Thank you both for your replies. It's a great relief to learn that nothing is fundamentally wrong with the layout of the main. I'm not qualified to replace the main and was hoping that nothing of the sort would be required (thanks for confirming that) but I didn't want to wind up in the situation where I'm applying bandaids to a gaping wound. I do understand fixture venting pretty well and it's my intent to leave things in a far better shape than I found them, with every fixture being properly vented. Right now, NO fixture is vented, with the possible exception of Bathroom 3 tub and toilet being vented (tub wet-vented) by the main stack. Which brings me to a very specific question: can any portion of the main that carries waste be part of a wet vent? For instance, can the sink in Bathroom 2 wet-vent the shower that joins the main a couple of feet upstream (with the usual constraints with regard to the vertical offset of the drain vis-a-vis the weir of the vented trap)? Can the same sink wet-vent the toilet that joins the main a couple of feet downstream?

    Thanks again!
    Last edited by Gordan; 02-02-2013 at 07:22 PM.

  6. #6
    Moderator & Master Plumber hj's Avatar
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    HOW the "wet vent" is connected to the system and other fixtures determines whether it is proper or not, the distances between fixtures is seldom a determining factor.
    Licensed residential and commercial plumber

  7. #7
    DIY Member Gordan's Avatar
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    Oh boy. I see that my question seems to repeatedly get lost in too much irrelevant detail that I provide, so let me ask it generally without any detail:

    Are there any requirements under the IPC for the main governing the use of the main as a horizontal wet vent, beyond those that apply to branch drains?

    I am interested in any differences stemming from the fact that this is the main and not a branch. I could not find any reference for special status of the main nor can I think of any reason why there should be - other than the likely higher volume of waste, which is not the case here because we're only talking about "any combination of fixtures within one to two bathrooms on the same level", but I acknowledge that codes have to cover the worst case and can't address every specific situation and that is why I ask.

  8. #8
    Test, Don't Guess! cacher_chick's Avatar
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    I for one would find a plumbing diagram helpful if it is advice or suggestions you are looking for.

    The code is quite specific in that only bath fixtures from up to 2 bath groups can connect to horizontal wet vented drain.

  9. #9
    DIY Member Gordan's Avatar
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    Here's a quick diagram of the current layout. I apologize for the crudeness of it. Bathroom 3 is the easiest to remedy; I would put the tub and the sink on the same branch, revent the sink, and wet vent the tub via the sink. Bathroom 1 is also relatively easy as I can put a separate vent to atmosphere on that one (it's in a different wing of the house and there's no practical way to tie it to the main vent.) Bathroom 2... is tricky. There's not really ready access to the attic from it from where the sink is located. I have to think on that some.

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  10. #10
    DIY Member Gordan's Avatar
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    Soooo...

    Now that I have posted the layout, would it be OK to please get some of that advice? :-)

    As I mentioned, my intention is to vent each bathroom group separately and fix what else is wrong with the plumbing (for instance, short ells on waste piping plane transitions.) I'll find a way. Once each bathroom group is adequately vented, however, will any issues remain with the main stack, or will it then be adequately vented? (It's 3" all the way from the roof penetration to the street.)

  11. #11
    In the Trades Tom Sawyer's Avatar
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    Theoretically each bathroom could use the lav to wet vent the other fixtures in the bath group but the reality may be quite different when you take into account the framing and what is above/below the floor and ceilings. Under the IPC, toilets only require a vent somewhere on the system (toilet to vent distance is unlimited) and the 3" stack through the roof is ok also.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  12. #12
    DIY Member Gordan's Avatar
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    Thanks, Tom!

    Yes, that lav in Bath 2 is a bit of a stinker when it comes to access to the attic. Worse come to worse, I may put a SMALL soffit along the sink-shower wall to house the sink vent and route it along the ceiling over to where the shower is - so, venting the shower and the sink separately. But there's one thing that I'm looking for under IPC which is the combination drain and vent. I would do this for one fixture only - the lav. In essence:

    - vertical drop from lav trap to under floor
    - horizontal run to shower drain
    - before discharge into the shower drain, a dry vent going up alongside the shower dry vent, and combining 6" above the lav flood level

    All of this seems legal according to section 912 of IPC, which says that "up to 8 fixtures" including lavatories (but not showers, hence the separate shower vent) can be drained-vented this way. And one is "up to 8." Thoughts?

    Separately from code-correctness, this section would in fact seem to legalize S-traps under specific circumstances, so... even if allowed to do it, should I shy away from this? Alternately, should I additionally stick an AAV on the lav even if it's not required? It seems that this would better protect the trap seal from discharge of the lav itself, while the downstream dry vent would relieve both positive and negative pressure from downstream fixtures and the main.

  13. #13
    Test, Don't Guess! cacher_chick's Avatar
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    Without knowing what is there to be dealt with, telling you how to run the vents would never work. Every trap needs to be vented, and the trap to vent distances must fall within the maximum allowed for each pipe size.
    Your existing drawing is very nice. If you were to draw in the vents, the pipe sizes, and the distances, then we could tell you whether you are heading in the right direction or not.

  14. #14
    DIY Member Gordan's Avatar
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    Cacher_chick,

    I absolutely understand what you're saying and that's why I'm not exactly asking for how to run the vents, but rather: IF there's adequate clearance to maintain code-mandated slopes, distances and fitting arrangements, would a such-and-such approach be allowed and, perhaps more importantly, would it be advisable. Codes are the bare minimum and, for instance, it seems to me that, although the combined drain and vent described under section 912 is ok, there might be issues with it in practice. So, a seasoned pro's "yeah, they'll let you do that but you shouldn't do it anyway because..." or "yep, that'll work well enough" is really what I'm after.

    I'll follow up with more specific drawings of what I'm proposing. I'm getting some ideas now so I want to measure things out and make sure I'm not missing something obvious and good due to a blind spot.

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    Test, Don't Guess! cacher_chick's Avatar
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    My first thought is that you must ask yourself "what is the fault, and what is the cause?". Are you planning to cut open all of your walls to install venting because you are bored, or is there something more to it? Depending on the existing pipe sizes and the amount of build up in the pipes, the combined drain and vent system can certainly have issues, which is likely why it is not currently used in the manner which your house is plumbed.

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