Revisiting Radon

by Brendan Kavanagh

Radon is often misunderstood, and understandably so as most people only think about it once when they are buying a house. When I ask homeowners what they know about their radon levels, the most common response is 'Yeah it was tested and the levels were.' While a low test is always a good sign, it’s typically only a snapshot of a short period of time in one part of the house. Today’s long-term radon monitors are easier to get and provide more detailed results, so we can now see how indoor levels fluctuate over time and across different spaces in our homes.  This new information is teaching us more about how radon levels can increase due to things like air sealing, exhaust fans, and even rain. With all that we are learning, it feels like the right time to revisit the important topic of radon risk in our homes.

What is radon?

Radon is a radioactive gas that is naturally occurring in the ground and can enter our homes most commonly through cracks and gaps in our foundation walls and slabs. It comes from the geology beneath our homes and can be found all over the U.S. Some areas are known to have particularly high levels; however, it’s not uncommon to find high levels in low-risk areas too. You can’t smell or see radon in the air, but prolonged exposure is estimated to be the number one cause of lung cancer in non-smokers.

How does it build up in my home?

The most common area to find high radon levels in a home is the basement. However, we sometimes find high levels on upper floors, particularly in buildings that are more airtight. In less airtight homes radon gets into the basement but is then diluted and cycled back out of the house via air leakage. In tighter homes radon levels can build up higher because there are almost always still pathways through a foundation for soil gas to get into the building but less constant air exchange through building air leakage to dilute or remove the radon levels. We tend to see higher radon levels in the wintertime because windows & doors are shut more often, and the warm air escaping out the top of a home creates a negative pressure zone at the bottom that draws in radon faster. Rain events also cause higher levels due to the raising water table pushing soil gas up from below and surface water blocking its path to the outside, making the path of least resistance directly into our buildings.

How much is too much?

No level of radon is considered safe; however, the EPA suggests that levels below 2 pCi/L are as low as we can reasonably expect to get with current technology. It’s commonly thought that only test results above 4 pCi/L are too high, but we should really be careful if we see anything above 2. Once we know what our levels are we need to assess what the exposure risk is depending on where the levels are highest. In unfinished basements that are only used occasionally for laundry or storage, the exposure risk is low. In finished basements or upper floors that are frequently occupied, and especially bedrooms, the exposure risk is much higher and should be addressed.

How/when should I test my home?

Airthings Radon Monitor

Ideally, we would recommend all homeowners buy a long-term radon monitor and set it up in the lowest area of their home that they spend long periods of time in. We use (and most commonly see) monitors made by Airthings, but any long-term monitor is better than none. Once you’ve let your long-term monitor run for at least 3 months, you can move it to different locations to see how the results change. If you must use a short-term monitor, it’s important that you follow the instructions very carefully and ideally test in the wintertime. If conducting any of this testing yourself is too much, you can also look for a professional radon tester in your area.

What should I do if my test results are high?

The only truly reliable radon mitigation system is a sub-slab suction or depressurization system. It consists of a pipe installed through your slab, connected to a fan, and run up to exhaust above your roofline. It works by capturing the soil gases from beneath your slab and exhausting them outside where they can’t be drawn back into the house. In existing buildings it’s typically only feasible to locate the fan and most of the piping outside the home. In new construction and in some renovations, you might be able to run the piping up through the house into the attic, where you would install the fan and then run the pipe up through the roof. While an internal radon system is less visually apparent on the outside, an external radon system can often be installed in discrete locations so it’s less noticeable; and you can paint them too.

Can’t I just seal up my basement walls & slab?

Any sealing you can do between your home and the ground will help reduce radon infiltration and make a sub-slab suction system more effective, but on its own, air sealing typically won’t get the levels low enough. This is most commonly due to cracks & penetrations in the basement slab that are difficult to durably seal. A new foundation with good vapor barrier detailing below the slab and up the walls can sometimes be effective, but very often there are areas that are not perfect allowing radon to get in.

Can I reduce radon levels with ventilation?

While traditional ventilation like exhaust fans and ERVs are sometimes suggested as radon mitigation strategies, they are not reliably effective and, in some cases, can increase radon levels. In addition, relying on traditional ventilation methods for radon mitigation would require you to ventilate more than you would otherwise, which can lead to high energy bills and discomfort due to both high and low humidity along with constant air movement.

How does Byggmeister address radon in our work?

We test our clients' homes both before and after each renovation or retrofit project. If we get a high result during the project planning process, we will incorporate a sub-slab suction system into our project scope. If we get a low result during project development but we are finishing a basement, we typically recommend planning for where a sub-slab pipe could go if needed down the road. It’s not uncommon for us to get a low result pre-project and a high result post-project. When that happens, we either install a sub-slab suction system, or our clients work directly with a radon mitigation company, like Eagle Enviromental Inc., to do this work.

All-in-all radon is a serious health concern that we are learning more about every year. We encourage all homeowners to understand their exposure risk and, if necessary, take steps to protect themselves. Radon risk is easy to ignore if you don’t know what to make of it, but if you’ve made it to the end of this blog, you know enough to take action!