Can I reduce the size of my main vent stack

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by cccrowe, Jul 20, 2007.

  1. cccrowe

    cccrowe New Member

    Messages:
    5
    I am currently remodeling a bathroom on the second floor of my house in San Francisco, CA. The previous bathroom had both a shower and bathtub. When I removed the shower, I found that the main vent stack was only partially in the wall (it is a 4 inch stack, and the wall is ony 3 1/2 inches wide), and the shower was built to disguise this. Now that the shower is gone, the only way that I can get the stack to fit in the wall is to reduce it from 4" to 3" as it comes up from the first floor. I am moving a toilet into the space wher et he shower was, and the space is 31" wide (rough), so I can't make the wall deeper, or I will not have the 30" wide finished opening for the toilet. I am headed to the library to check the code, but thought that if anyone knew the answer, it would save me some time. Thanks

    Chris
  2. MattAlexander

    MattAlexander Plumber

    Messages:
    6
    Location:
    Fresno CA.
    Lol!!!!!!!!

    First of all how many fixtures is that 4" vent carrying total? Is this the only vent coming up through your roof? I imagine that vent is carrying a toilet,sink shower and tub right? If thats all its venting then yeah I'd say reduce the pipe to 2". so you will have a toilet,tub and sink venting out a 2" line. That will be fine.
    If you cant do this due to more fixtures through out the house being tied into
    this 4" vent I'd say its time to fer the wall out to make room for your vent and say good bye to 31" of toilet space!!!!!!!!!!!!!!!LOL. Is this being inspected?
    Last edited: Jul 20, 2007
  3. cccrowe

    cccrowe New Member

    Messages:
    5
    Sorry, I should have mentioned that the stack only carries the toilet. However, I found in the plumbing code that the main vent needs to run "undiminished in size" from the building drain to the open air... no it's not getting inspected, but if I want to build out my basement at a later date, the exposed plumbing needs to be up to code. Thanks for your input.
  4. as it comes up from the first floor, is it a vent or a waste drain there? Can you reduce the size of the vent in the first floor wall too, now or soon after?

    david
  5. cccrowe

    cccrowe New Member

    Messages:
    5
    The vent stack comes out of the floor underneath a beam that runs the length of the house. There are rarely basements in San Francisco. The first floor is unfinished space/garage, so the stack is not in a wall. The stack rises ~ 7 feet out of the floor, has a 1/4 bend, goes two feet, then a Tee, the vertical section of this Tee is a continuation of the vent and rises through the wall above (but not completely in) and exits the roof. The horizontal section of the Tee continues about two feet and attaches to a closet bend for the toilet above. All of this is with 4" cast iron. I want to reduce the vertical section from the Tee to the roof from 4" to 3" so that it will fit in the wall on the second floor. The only drain on this stack is the toilet. and it is on the second floor, so the section of vent stack from the first fllor to the section floor acts as a waste drain for the toilet.
  6. cccrowe

    cccrowe New Member

    Messages:
    5
    I could reduce the stack from in the concrete floor, I have broken the concrete over the pipes in the first floor, just to verify that they have not broken (1927 house in earthquake country).
  7. BAPlumber

    BAPlumber Plumber

    Messages:
    227
    Location:
    Vashon, Washington
    are any other vents tying into this in the attic or wall? how many other vents through the roof do you have, and size? how many bathrooms (including powder rooms) do you have? If you change the 4" to 2" you may have to increase the other vents or add vents.

    The cross sectional area of the vents need to equal the area of the required building drain.

    Brent
  8. cccrowe

    cccrowe New Member

    Messages:
    5
    The only thing that ties into the main stack, above the concrete slab, is the toilet. This is a one bathroom house. The kitchen sink has it's own independent vent. The bathroom sink and tub are also vented separately.
  9. BAPlumber

    BAPlumber Plumber

    Messages:
    227
    Location:
    Vashon, Washington
    If your kitchen sink, lav, and tub are individually vented through the roof you can vent your water closet with a 2" vent. since it is individually vented.

    if your lav and tub are a combined vent (1.5") then your KS vent must be a 2", the drain must also be a 2" (required by code).

    There are so many variables here that a right answer is hard. California uses the UPC, so do I, so I know a little about your code.

    The main thing here is you may want to expand in the future and need to plan for it.

    try this, vent the toilet with 3". Provide a 2" Branch to the basement for a future vent. make sure the branch is above the flood level of the toilet.

    Brent
  10. srdenny

    srdenny Plumbing Contractor

    Messages:
    361
    Location:
    SF Peninsula
    CCCrowe
    A word of warning: San Francisco has a number of addenda to the California Plumbing Code. I believe one of them is a requirement for a full sized vent stack and not just an aggregate cross section of multiple vent pipes, as is allowed by the UPC.
    Call one of the inspectors on this list. http://sfgov.org/site/dbi_index.asp?id=44473
    Ask them your question. You can preface it by explaining that you are a HO planning a project and the 4" stack effects your layout and if it can't be reduced in size you might reconsider even pulling a permit and attempting the project.
    Last edited: Jul 21, 2007
  11. Winslow

    Winslow Plumber

    Messages:
    450
    Location:
    Hawaii
    most counties ammend the plumbing code they use. The UPC is used by many juristictions and each ammend according to their local area. Here in hawaii the state legislature prints their own code. Which in reality is the UPC with their ammendments. (The first thing it does is enact the UPC, then adds changes)
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