Friday, July 29, 2016

Passive House and Radon

Passive House and Radon
Let me 1st start by saying - I am not Certified in anything Radon. I don't know what goes into the analysis in the lab and I only followed the instructions on the package. 

Here is what I do know:

  • Radon is a radioactive soil gas that can cause cancer. 
  • Radon is a "heavy" gas
    • Molar weight of 222 g/mol vs 44 g/mol of CO2

  • The major sources of Radon in homes (mostly basements) can be attributed to:
    • Open Foundation Block cores
    • Dirt Floors
    • Cracks in your foundation
    • Open Sump Pump Crocks
      • When your drain tile is not filled with water, it is filled with soil gas (ie Radon)
Basically direct any connection between the soil and your home can lead to Radon in your home.

Mendon, NY has been identified as an area with high Radon levels (39-51% of the homes have greater than 4 pCi/L). It was certainly a concern for me from the start. A passive house is suppose to be super tight, thermal bridge free, and properly ventilated, but if Radon seeps into the house it could be a huge problem!

       In a typical home for this area you would see a Radon Mitigation system installed constantly removing the air from your drain tile with a constantly running fan. This would hurt our auxiliary electrical use for certification, and I was unsure how it would effect the overall ventilation system inside the house (if at all).
      You would also see a sump pump inside the house. I couldn't figure out how to make a sump pump crock "Thermal Bridge Free", nor air tight (to the Passive House level of air tight).

     As I have written about before - we elected to Passively prevent Radon into the house with proper fabrics, air tight construction from the slab up and eliminate the interior sump crock (We moved the sump pump to the outside)

     We are finally at the point where we can perform a few Radon Tests to ensure we are Radon Free.
I conducted 2 tests, 1 in the basement and the other in the exterior sump crock.


For the sumps crock test I dropped the test canisters into the sump crock with a long string. I measured it to be a few inches above the sump pump. There were 2 tests, one was about 3 inches above the sump pump and the other was about 12 inches above the sump pump.

In the basement I simply set them on a box a few inches off the floor and a foot or so away from the walls (as the test instructions told me to do)

I did deviate from the instructions in 1 way. I left our Zehnder Ventilation system operating - as it is needed to provide the house with fresh air 24/7. It was only running in Medium, and there is no exhaust in the basement - only 1 supply, The extracts are on the 1st and 2nd floors. I understand this will effect the tests, however I am most interested in finding out how high the radon is under "normal" conditions. There is no reason to ever turn off the Ventilation system.

 What about a long term Power Outage?? Well - for those who have a powered radon mitigation system I'd have the same question. I think Radon in that case would be much lower on my worries list. We have basement windows. I'd be more concerned with the food in the refrigerator or the hot water.

ANYWAYS.... Back to the test results:

According to Pro-Labs:

Sump Crock Canister #1 (Closest to Sump Pump) - 2.4 pCi/L
Sump Crock Canister #2 (12" Above Sump Pump) - 0.8 pCi/L

Basement Canister #1                                          - 0.1 pCi/L
Basement Canister #2                                          - 0.1 pCi/L

While Radon many not be a huge problem - I am very pleased to see such a low number in the house!

 I would certainly not have changed anything with our design - it may have saved a few dollars but the use of the Radon Barrier in my mind is totally worth it!


  1. Enjoyed reading this blog, just want to clarify is the house here certified passive house ?

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