Replies

1. 
   FrankD | Nov 03, 2024 02:17pm | #1

   If you are in the US, there are radon maps at https://www.epa.gov/radon/epa-maps-radon-zones-and-supporting-documents-state.

   I believe the IRC only requires installation of a radon mitigation system in zone 1, but the EPA also recommends it in zone 2.

   In zone 3, you can ask the building department or neighbors if they've had any radon issues. But given the difficulty and expense of retrofitting a system below a slab on grade, I think it's worthwhile putting in the vent pipe even in zone 3. You should have a poly vapor barrier anyway, and the pipe is cheap enough. You just need 4" of coarse aggregate to bury it in, and the builder might be doing that already.

1. 
   pmny | Nov 03, 2024 03:07pm | #2

   Thanks Frank.

   Yes, I'm in Dutchess County NY which is in zone 1 based on your link.

1. Expert Member
   Michael Maines | Nov 04, 2024 09:40am | #5

   In that case I would absolutely include a passive radon mitigation system. Many people, including builders, don't believe that radon is a high risk because it's colorless, odorless and rarely causes symptoms in the short term. But it's the leading cause of lung cancer among non-smokers.

1. 
   pmny | Nov 04, 2024 10:04am | #6

   Thanks Michael, good advise.

2. Expert Member
   Akos | Nov 03, 2024 03:53pm | #3

   Lets look at where a typical radon system starts.

   You have a bed of gravel under your slab with poly above it. A length of perforated pipe in the gravel bed.

   Now if you look at the above, that is exactly what you need to have for proper water drainage and moisture management. If your drawings don't already have this, add it now!

   Once the water management is done, the only additional thing you would need for radon mitigation is a pipe connected to this perforated pipe run above the roof. The cost of this is so small, that it is not even worth not adding it in.

1. 
   pmny | Nov 04, 2024 10:04am | #7

   Thanks Akos, I've passed your advise on to my builder.

3. Expert Member
   BILL WICHERS | Nov 04, 2024 08:57am | #4

   Typical radon systems just depressurize the existing footing drain (typically perforated pipe which may or may not be corrugated plastic pipe), and that system is put in place to keep water away from the foundation and footing. If you have a sump pump, you just add a sealed lid and you're usually ready to go after adding a vent pipe and fan.

   As Akos mentioned, slabs should have a gravel drainage layer with a poly membrane under the slab, and that acts as a collection area for radon, with the polyethylene membrane preventing the radon from getting to the structure. The perimeter drain ties into that gravel bed, so the radon fan depressurizes the gravel bed. This ends up depressurizing the entire area under the slab, which draws off any radon that might be coming up from the ground -- exactly what you want!

   Basically the things you need to put in to deal with water are the same things you need to deal with radon, you only need to add a vent pipe and fan. It's common to run a 3" PVC pipe from the perimeter drain up through the roof to act as "passive" radon system (stack effect alone handles the "depressurization" part). If that alone isn't enough to keep radon levels under control, you can add a radon fan (usually in the attic), to convert the "passive" system into an "active" system. If you think you may need to do this, you want to make sure there is an accessible area of that 3" pipe, and you should pre-install an electrical outlet near it to power a future fan. Note that the fan needs to be located OUTSIDE of the living areas of the home, which means in the attic (if vented), or outdoors. You aren't supposed to install the fan in the basement, and you shouldn't install it in a conditioned attic, either. The fan needs to go OUTSIDE of the building envelope.

   Bill

1. 
   pmny | Nov 04, 2024 10:05am | #8

   Thanks Bill,
   Much appreciated, I've passed this along to my builder.