We ordered a radon test kit from the New York State Department of Health last month. The kit is small canister of charcoal that you open and place in the test area for several days. We let it sit for 4 days in our basement, then sent it off to the testing lab. The results came back about a week later.
For reference, the EPA defines the safe limit of radon gas at less than 4 picocuries per liter of air (pCi/L). Our result was 38.6 pCi/L, almost 10 times the limit, ouch!
We had been somewhat slow to get the basement tested for radon because we spent a great deal of time and care sealing everything in the basement. Our blower door test confirmed that we had done a good job overall. So we assumed we would have no problems with radon.
Unfortunately, the radon is getting in, and because the house is so tight, it’s not getting back out.
Thankfully, we installed vent piping under the slab and sub-slab insulation when we built the house. We capped it off at the surface hoping we wouldn’t have to use it.
How sub-slab radon mitigation systems work
A vent pipe installed below the slab and vented to the outside depressurizes the area below the slab. Radon gas will take the easiest route to the outside. Our vent pipe runs the full perimeter of the inside of the footing under both the slab and 6″ of XPS insulation (R-30).
The EPA recommends running the vent pipe up the center of the house to the outside because the warmth of the house creates a stack effect, inducing a natural draft in the pipe without using mechanical ventilation. Unfortunately this method also cools the house in the winter, something we hoped to avoid.
So rather than run the vent through the house, we ran our exit vent pipe through the footing to the outside of the foundation wall and capped it at surface level. We figured if/when we determined we had a radon problem, we would extend the vent pipe up outside the house, through the soffit, into the attic, connect to an inline fan and exit through the roof.
The fan will use energy continuously but at least it won’t be cooling the house in the process. The installation cost will be minimal since we did most of the hard work when we poured the foundation.
In hindsight, we should have found a way to integrate the vent into an outer wall where it could still be insulated from the interior space. Running the vent up the outside of the house will take some work to make it not look like a strange pipe on the side of the house. We’re going to try to disguise it as a gutter. We’ll have more info on the details and photos as we start work next month.
For more information on radon in the home, read this EPA guide, A Citizen’s Guide to Radon.
Up Hill House 
Test your water for radon too. Ours was very high, like 10x too high. (Our Board of Health required the test…) Added an Radonaway EZ95. All better. Erik
Testing for radon in the water was on my list. You just convinced me to move it to the top of the list. Thanks Erik!
Just got test results back for radon in water. Very low level detected, 126.1 pCi/L. The limit in Massachusetts is 10,000. The lowest limit is New Hampshire at 2,000 pCi/L. So I think we’re good. Relieved.
larry..how did you make out with the radon mitigation system?..i have a new 28kbtu load timber home in northern mass area and one test showed levels similar to yours…how much juice does it use and how low did it lower levels?..also i found a concrete sealer product that seals and tightens crete for better results..did you use that type product?..thanks for input…
Hello there. Thanks for asking. In all honesty, I haven’t done a darn thing about it yet. We started thinking about extending the ERV ventilation to the basement for an exercise room. Since the ERV is in the basement, it shouldn’t be difficult to extend the ducts. But I haven’t done enough research to know if this will decrease the radon levels enough, or how much of hit to the overall energy budget this will impose. Sorry I can’t answer your question yet. I can say we didn’t use a concrete sealer. We used a layer of poly sandwiched between the layers of insulation under the slab. I still don’t have a good understanding of where the radon is getting into the basement.