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Community and Q&A

Pipe for Radon Mitigation System

arnoldk | Posted in General Questions on


Having read a bunch articles on Radon, there does not seem to be a clear indication as to the location and length of perforated pipe (corrugated Big “O” or PVC Schedule 40) that should be installed.
Most of the article I have read simply seem to indicate placing a Tee connector under the slab with gravel around and some indicate an optional of adding a length of 4-5 feet perforated pipe on either side of the Tee connector.

Any feedback as to what is the best option and material to use?
Attached is my slab on grade drawing showing two option (blue & red) as to what I was considering doing.

Thank you,

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  1. Expert Member
    ARMANDO COBO | | #1

    On a basement or conditioned crawl space, I always specify socked drain tile on both sides of the footing going to a sealed sump pit. Somewhere in the middle, I cross the basement with draintile down the middle and with a “T” to vent straight up thru the roof. If the radon levels are high or the home is very large, we install two. If radon levels are high, we also install an exhaust fan.

    1. arnoldk | | #2

      Do you treat slab on grade the same way as you do for basements?


  2. Expert Member
    ARMANDO COBO | | #3

    I do, especially if we know we have high levels of radon, and since I need to install drainage anyways.

    1. arnoldk | | #4

      That makes sense. In my case, there is no drainage required since the house (slab) is sitting over 12 inches above grade.


  3. arnoldk | | #5

    Does anyone know if the vent pipe must go through the roof or if code allow it to exit through an exterior wall without any operable windows or other vents/exhaust?

    Thank you,

    1. Expert Member
      Michael Maines | | #11

      It is required to extend at least 12" above the roof deck and should be located close to the ridge, plus a few other things:

  4. Expert Member
    ARMANDO COBO | | #6

    You should read 2021 IRC Appendix AF Radon Control Methods and Section AF103.6.1 Vent pipe requirements. There are different techniques required in areas where designated by the jurisdictions.
    Another option? Talk to your Building Dept.

    1. arnoldk | | #7

      Thanks Armando and I'll read up about it.

      Our building department is short of useless and I have tried on two occasion to communicate with the building inspector assigned to me build with no response. It sounds this is pretty typical in my area according to others in my city, at least for the last few years.


  5. walta100 | | #8

    It seems to me you have a lot of pipes under that slab in both plans.

    I do not think that much pipe is necessary assuming there will be 6 inches or so of clean gravel under the slab the air spaces between the gravel should allow the radon to find the low pressure in your stack pipe.

    Seems to me the red perimeter system is likely to pull air from outside of your building much of the radon it would vent would never have enter the building but for your vent.

    I think your vent stack should be in the center of the home and not near the edge as shown. I think this vent pipe should be as long and straight vertical as possible. I would not install a fan unless or until it was clear that natural stack affect from the long vertical pipe was insufficient to control your radon.

    You might consider having twin systems with separate collection pipes vent stacks.

    1. arnoldk | | #9

      Hi Walter,

      I only plan to rough-in the system since it's cheaper to do it now compared to after construction is done. There will be around 12 inches of packed gravel since the slab on grade is being built a bit higher than the surrounding grade.

      I was hoping to put it near the center of the house and simply run one 10' pipe on either side of the Tee fitting but I cannot find a spot where the wall line up to pass the vent pipe through.

      Thank you,

  6. hallie17 | | #10

    Thanks for asking about this Arnold. I was just wondering about it.

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