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Thread: Bath remodel - venting questions

  1. #1

    Default Bath remodel - venting questions

    I am in the process of remodeling our bathroom which involves a full reconfiguration of the shower and toilet drain and vent systems. Our house is on a pier and beam foundation with 15" of crawl space.

    I have several questions and have included a picture below to help articulate the scenario and my proposed solution.

    Issue: The toilet will be located in the corner of the house and I want to avoid venting up either of those two walls. A copper 1 1/4" vent is already there for the lavatory and I'm leary about increasing to 2" (if that is even an acceptable size for venting a toilet and a lavatory- is it?) due to the fact that it is an exterior wall. Therefore, I am proposing to vent off the drainline vertically and then horizontally within the crawl space to an interior wall about 7 ft away. The shower would be configured similarily and will use the same vent as the toilet at the interior wall location. So, my question is whether or not this is an acceptable venting method. If it is, will a 2 " pipe size for the vent be acceptable for venting the shower and the toilet? Also, I'd like to use the existing vent hole in my roof; under my proposed scenario, could I run the vent horizontally again in the attic and then vertically exit through the roof?

    Any help would be appreciated. I've read books upon books and none of them have a solution for my dilema.

  2. #2

    Default Here is the attachment with the picture.

    Sorry, first time user- here is the picture attachment.
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  3. #3
    Forum Admin, Expert Plumber Terry's Avatar
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    The shower and the toilet can not be vented together until you are 6" above flood level of the fixtures.

    You certainly can't join them below floor level.

    That means for the toilet and the shower, you would run two seperate vents up a wall until you reach 22" above the floor. If you are adding the lav, then you would join at 42".

    All fittings below the flood level must be installed for waste lines.
    That means that horizontal fittings should be wye type fittings and 45's.

    A shower can be vented with 1.5"
    The toilet needs at least a 2".

  4. #4

    Default

    Thanks for the quick reply Terry. So, based on your response, it can be done with modification?? I have modified my plan and included it in the attached. Does this accurately reflect your suggestions?

    Thanks again,

    James
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  5. #5
    Moderator & Master Plumber hj's Avatar
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    Default Vents

    You are going for overkill. The toilet and shower vents can be installed side by side and then connect together at a point 42" or more above the floor. It appears that this may be the only plumbing system in the house, other than the kitchen. If so, then most codes would require that the sum of the areas of all the vents through the roof equal that of the 3" cast-iron sewer.

  6. #6

    Default vents

    Please forgive my ignorance (this project is my first involving this amount of plumbing), but what do you mean by overkill? Are you just referring to the routes of each of the vents (shower and toilet) and that they could be routed up the same wall? Would you suggest something in the alternative?

    Also, I don't follow your last comment about "the sum of the areas of all the vents through the roof equal that of the 3" cast-iron sewer". Can you elaborate on what you mean? Our house has the following vents: 1 1/4" for washing machine, 1 1/4" for the kitchen, 1 1/4" for main bath lavatory, 2" for main bath toilet and bath combined, 1 1/4" for the master bath(as seen on the drawing) and the yet to be determined vents for the master bath for the shower and toilet (as seen in the drawing).

    Thanks for the help!

  7. #7
    Moderator & Master Plumber hj's Avatar
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    Default vents

    It is "overkill" because you are running all of them up to the "attic" and then tieing them together. The shower and toilet vents can come up in the same wall right next to each other and then tie together at a point 42" above the floor, (not in the attic). If you could install the pipes that way, then you could even pipe them to the lavatory and tie them all together at 42" above the floor and run a single 2" vent through the roof. For the purpose of sizing a combined vent you can just square the radius and add the sums together. A 3" vent has a value of 2.25 so any combination of vents that give a value greater than that will be adequate. A 1 1/4" vent has a value of .39 so five of them will add up to 1.95. Add the value of 1 for a 2" vent and you get 2.95 which is adequate even without the 2" which you will run for the new toilet and shower. If that 2" vent tied into the 1 1/4" lavatory one then it would have to be 2" through the roof, but would not affect the total vent area negatively. For computational purposes only vents that actually penetrate the roof are counted, not any that tie into them in the attic.

  8. #8
    Forum Admin, Expert Plumber Terry's Avatar
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    Most of the time, you would try to keep the pipe close together.
    We would try keep the travel time crawling in the attic and crawl to as little as possible.

    There is less drilling and pipe that way too.

    The area of the pipe is as follows, I hope my math is good.
    4" = 12.5664 square inches
    3" = 7.0686 square inches
    2 = 3.1416 square inches
    1.5 = 1.7672 square inches
    1.25 = 1.227 square inches

    For most homes with up to three toilets, you would use either a 3" vent through the roof or two 2" vents and one 1.5" vent through the roof.

    For homes with four or more bathrooms, you would use a 4" vent or four 2" vents.

  9. #9
    Moderator & Master Plumber hj's Avatar
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    Default math

    Your math is good, but out in the field without a calculator, you can dispense with PI since it is a constant and thus can be eliminated. 2" has a value of 1, 4" has a value of 4 and four 2" pipes equal a 4" one either way.

  10. #10
    Forum Admin, Expert Plumber Terry's Avatar
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    Hey! I thought I said that, but with different numbers.

    I like your way too.

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