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eframe_gw

Venting at Toilet

eframe
17 years ago

I am remodeling an upstairs bathroom, and ran into a problem with the inspector. Apparently I didn't re-vent the downstairs toilet which is now sharing the same waste-vent stack as the upstairs bath group. I did revent the shower downstairs (so right now, only the toilet is in question.)

So my question is, what is everyone's experience with this as a requirement? I've found numerous waste/vent diagrams that have the toilet system the way I do - without the toilet vented separetly, or above incoming waste. My initially assumption when I started the project is that sharing the vent wouldn't be a problem because the pipes were so big (4"). Now that I've had to dig into it deeper, it looks like any additional work I do will be in very limited space and with cast iron, so I'm especially not very excited about it.

In the end, I know it comes down to what the inspector wants to require, and that codes differ by area. I hate to do extra work for no reason though, and would like to know if I'm right or not.

On another note, the inspector wants me to run thruogh a test of the system with him, which I am also perplexed about because at the moment there are several points in the system that I don't have a way of plugging up. From my point of view, the reward vs risk for most of this isn't worth it, at least not with a 100 year-old house.

Comments (12)

  • kudzu9
    17 years ago
    last modified: 9 years ago

    Sometimes inspectors try to get people to make changes that are -- arguably -- improvements, but that aren't absolutely required by code. The last time I suspected something like this, I politely asked the inspector to show me in writing what the code required. When he showed me what he thought the requirement was, it was clear that the change wasn't absolutely required. If I were you, I'd start with seeing it in writing.

  • lazypup
    17 years ago
    last modified: 9 years ago

    You want to see it in writing,,no problem.

    International Residential Code IRC 3107.3, T3107.3
    Uniform Plumbing Code UPC908.1 & 908.2

    When fixtures on different levels are connected to a vertical stack the section of the stack between fixtures is classified as a wet vent.

    Toilet cannot be the upper fixture on a wet vent.

  • jason1083
    17 years ago
    last modified: 9 years ago

    so then he just needs to revent the downstairs toilet? or does he need to completely redo everything.
    Sorry for asking (I am not questioning you), I just have seen many setups done this (obviously wrong) way.

  • eframe
    Original Author
    17 years ago
    last modified: 9 years ago

    The inspector wanted me to reroute the waste from upstairs through a new 3" pipe to below the connection in the main stack with the bottom floor toilet. I got him to agree that I could also vent the bottom toilet before it gets to the main stack (as you pointed out). The problem with that plan is that the toilet is backed up against the main stack already, so there isn't much room to add a new fitting off for a vent.

  • lazypup
    17 years ago
    last modified: 9 years ago

    To be code correct one of two things needs to happen.

    1. The uptairs toilet could be connected to a separate stack as was described by the inspector or:

    2. A vent needs to be installed between the downstairs toilet and the stack.

    The theory here is, A direct line from the toilet to the stack is classified as an "unvented fixture arm" and an unvented fixture arm may not be attached to a stack if there is a toilet above the point of connection on the stack. By placing a vent on the lower toilet fixture arm the portion of pipe from the lower toilet to the vent is now the fixture arm while the remaining section of pipe from the vent to the stack is a "Vented branch" which may be attached below a toilet.

    If they are under the International Residential Code option two presents another problem. When a vent is attached to a horizontal pipe parallel to a stack there must be a minimum of 10x the pipe diameter separation between the vent and the stack. I.E. if the horizontal line from the toilet is a 3" line their must be 10 x 3" = 30" separation from the stack to the vent.

  • pinocchio
    17 years ago
    last modified: 9 years ago

    I have never dealt with the curious fixture called a bidet. But I wonder if they are classified as a toilet? Considering they are intended to be used as a shower, thats what IÂd expect. However, considering their dedication to human waste, the toilet-classification makes sense.

    I realize that these fixtures are generally set side-by-side, so that they would both use the same fixture arm. That does raise the other question of whether the toilet, in that case, needs to be the last fixture?

    Pinoke

  • lazypup
    17 years ago
    last modified: 9 years ago

    You are correct that a Bidet is mounted on a closet flange in the same manner as a toilet.

    The closet flange must be connected to a 1/4 bend to transition from vertical to horizontal. Once the lines are horizontal they may be combined by means of a Wye or Wye & 1/8 bend but a closet flange may not be connected to a Wye & 1/8 bend with the side opening in the vertical plane.

  • lazypup
    17 years ago
    last modified: 9 years ago

    Code prohibits installing a Tee on a horizontal line. Whenever it is necessary to connect a branch line to a horizontal line we must make the connection by means of a Wye with the side inlet of the Wye positioned to direct the flow from the branch in the downstream direction as it enters the line. In this manner it insures the velocity of flow will remain constant. If the connection was made by means of a Tee the liquid discharging from the branch would enter the line and hit the opposite wall of the line which causes the liquid to momentarily stop as it changes direction. Not only would this retard the velocity of flow but it also causes a small amount of the liquid entering the line to momentarily backflow upstream in the line. The concern here is that solid particulates in the flow could be carried slightly upstream and as the liquid stops, then reverses its flow downstream again there is no longer sufficient velocity to convey the solids which would then remain just above the joint in the line causing the line to clog. (If you would like an illustration send me an email and i will return you one.-perhaps someone more adept at posting illustrations would like me to send it to them and they can post it for me.)

    By necessity there is always a single line connected from the fixture trap to the vent which is properly defined as the "Fixture arm". The fixture arm serves as both the drain and the vent for the fixture however in order to insure proper venting the minimum allowable length of a fixture arm is 2x the pipe diameter.

    The method used by the International Residential Code to determine the maximum length is the simplest to understand so for the purpose of illustration let us examine the IRC method.

    Keep in mind that all lines 3' or less in diameter are required to have a 1/4" per foot pitch. The IRC states that the bottom of a fixture arm at the trap weir may be no higher than the top of the fixture arm at the point where is connects to the vent. From this we can easily determine the maximum length of the fixture arm by dividing the diameter of the pipe by the pitch of the run. By example, consider an 1-1/2" line with a 1/4" pitch. 1.5" / .25" = 6'. We must be very careful when running a fixture arm to insure the pitch is correct. If the pitch is less than 1/4"/ft the velocity of flow will not be sufficient but, if we increase the pitch it shortens the allowable length of the fixture arm, by example let us consider an 1-1/2" line run with a 1/2" per foot pitch. The maximum allowable length would now be 1.5"/ .5" = 3'. (you may rest assurred that inspectors look at this with a critical eye).

    When the length of the fixture arm exceeds the maximum allowable distance we must then install an auxillary vent within the prescribed distance. With careful layout it is possible to vent an entire bathroom group with only one vent.

    The Uniform Plumbing Code uses fundamentally the same mathematical method but they then derate the allowable length by approximately 40%. Under the UPC the maximum lengths are:

    1-1/4" pipe................2'6"
    1-1/2" pipe................3'6"
    2" pipe....................5'
    3" pipe................... 6'
    4" or greater pipe........10'

    The actual purpose of venting a trap is to insure the water is not sucked out of the trap during the drain function. For this reason S traps have now been outlawed, however, if you examine the cross section of a toilet trap you can easily see it is the exception that proves the rule. The trapway in a toilet bowl is in fact an S-trap and it relies upon the syphon effect to suck the water out of the bowl and up and over the trapway. This also explains why all toilet fill valves are required to provide a "Trap Primer" function to restore the water level in the trap after the flush is completed.

    Placing a toilet on a quarter bend enhances the syphon effect insuring a better flush. In fact, the IRC has an exception that states that if the toilet is the only fixture served by the fixture arm it may run an indefinite length without requiring additional venting.

  • timo888
    15 years ago
    last modified: 9 years ago

    Would it be accurate to say that the toilet shown in the diagram (see link below) is serviced by a vent whose effective diameter is 4-inch ? Do two 2-inch pipes provide the same amount of air as one 4-inch pipe?

  • andy_m
    10 years ago
    last modified: 9 years ago

    This is an old thread, but as a mechanical engineer, I wanted to comment that there is a ton of misinformation regarding venting, particularly toilet venting, on the internet. Lazypup seems to be one of the very few - even in the ranks of pro plumbers - that actually understands this topic and how toilets work. If you lay out your DWV system to meet code AND enhance siphon action from the toilet, you'll be pretty happy with the results. If you vent it without considering siphon action, it'll work but it won't be a top performer. I would say, re-read lazypup's post and do it like he suggests. Bravo, pup!

  • bus_driver
    10 years ago
    last modified: 9 years ago

    The poster identified as Lazypup died some time ago. He posted here frequently after his health ended his active days in the trade. In my estimation, tradespeople can and should be professionals and when they are, recognized as such with all the respect given any professional.
    "The society which scorns excellence in plumbing as a humble activity and tolerates shoddiness in philosophy because it is an exalted activity will have neither good plumbing nor good philosophy: neither its pipes nor its theories will hold water."
    John William Gardner (8 October 1912 �" 16 February 2002) was President of the Carnegie Corporation and Secretary of Health, Education, and Welfare under President Lyndon Johnson.