10 Comments

1. 
   qofmiwok | Oct 01, 2021 08:23pm | #1

   So the implication is the "makeup air" from the active radon system is coming from the basement/crawl causing it to go negative? Therefore impeccable air sealing would prevent that?

   My radon/vapor barrier is being sealed to the footing before pouring the slab, but I am still planning to seal all the slab/footing connections with Tremco Acoustical Sealant to have that concrete air barrier. The outside of the house is all covered with self applied membranes from the footing up and over the house and back down. Plus additional spray foam at rim and ceiling joists, and sealant at the sill. So the air "should" flow directly from the sub-slab gravel up through the radon pipe without pulling air from within the house and creating negative pressure, right?

   How does a radon vent (and worse yet an active one) affect the airtightness performance of a super tight house?

1. 
   Randy_Williams | Oct 02, 2021 08:18am | #2

   That's a great question. If all the details are done correctly, there should be no, or very little connection between the sub-slab radon system and the home. During blower door testing, I've found this is not always the case. Leaking around the pipe penetrations and the tub and shower drain boxes commonly used is something I'm seeing. I found one by dumb luck a couple years ago and now I check these areas when they are accessible during a test. My advice is to perform a blower door test during construction, as early in the process as possible and pay attention to all the penetrations through the concrete. They still can be easily sealed at this point.

   What can happen if a radon vent (active) is causing a negative pressure issue inside a home? The answer to most building science questions is it depends. In a very cold climate, you may end up with a condition like Gary Nelson, over ventilating which can cause a home to become dry during the winter months. In a hot and humid climate, you may be dragging in humidity. Both may affect energy costs.

   Thanks for the question!

1. 
   qofmiwok | Oct 02, 2021 09:52am | #3

   Can you give more details about the tub and shower drain boxes? Are you referring to plumbing stack vents?

   When you do blower door testing do you do it with the radon system running or off?

1. 
   maine_tyler | Oct 02, 2021 04:40pm | #4

   drain boxes are holes in the concrete for installation of drains. He's just saying some people are installing these and not properly sealing them, creating air passageways between the basement interior and the sub-slab region. Make the floor an air barrier, is what it comes down to.

1. 
   qofmiwok | Oct 02, 2021 05:13pm | #5

   Gotcha. Thanks!

2. 
   Randy_Williams | Oct 03, 2021 07:24am | #6

   Thanks Tyler!

2. 
   nick_vk | Dec 29, 2021 11:23pm | #7

   The statement that in existing homes, action is needed only if the radon level is above the 4 pCi/l leaves some important information out. From the EPA's radon info website: "EPA recommends homes be fixed if the radon level is 4 pCi/L (picocurries per liter) or more. Because there is no known safe level of exposure to radon, EPA also recommends that Americans consider fixing their home for radon levels between 2 pCi/L and 4 pCi/L."

3. 
   Randy_Williams | Dec 30, 2021 06:40am | #8

   Thanks for that clarification, Nick.

4. 
   ryhow | Aug 09, 2023 05:09pm | #9

   Probably an obvious reason not to do this I'm missing, but why are we not prepping for radon by routing the exhaust pipe out to the side of the slab instead of a stub pipe through the slab? Seems a whole lot tidier and with less risk of messing up the details.

1. Expert Member
   MALCOLM TAYLOR | Aug 09, 2023 06:01pm | #10

   RyanHow,

   If the pipe is routed out the side of the slab, you end up with a set-up like you see in the first photo, with a vent stack or fan on the exterior of the house. Much like we did with other plumbing vents which traditionally ran on the outside of the walls, it makes more sense to route them internally and out the roof.