When it comes to radon mitigation systems, it is important for you to know if the system in your home is passive or active. If you have concerns about whether or not your home’s system is properly reducing radon levels, the professionals at HomePro Inspections want you to know that radon testing is the only way to make that qualified determination.
Since 2009, Minnesota has required that all new homes be built to be radon-resistant. New home construction must use techniques and materials to help reduce or prevent radon from entering the home. A passive system relies on the natural upward thermal flow of sub-slab air and soil gases through a pipe to the home's exterior.
What is a passive radon mitigation system?
A passive system starts with a perforated tile system set in permeable soil, such as gravel or pea rock, which is covered and sealed with plastic before the concrete floor is poured. Typically, a three- or four-inch PVC pipe vents the system. The PVC pipe extends from beneath the concrete slab, up through the house and attic space, to the exterior of the home. Based on the thermal stack effect, the system will naturally draw air upward. The home acts as a vacuum on the soil due to internal and external temperature differences. There are many factors, including weather, storms, winds, barometric pressure, type of construction, and so on, but that’s another discussion best left for another time.
Why would my passive radon system not be enough?
Radon, a radioactive gas that is generated from the naturally occurring process of uranium decay, is found everywhere in Minnesota. Generally, a home with a passive radon system experiences high radon readings due to three factors. They include pressure differences between the inside and outside of the house, the way radon enters the house through the soil, and the soil's actual radon level.
On occasion, the construction process unintentionally obstructs a system. An unobstructed system is critical for adequate and consistent airflow under the slab.
To help understand variations in radon levels, I’ll use my house, a one-story slab on grade in 2017, as an example. I oversaw the installation of the passive radon system and can confirm it was done correctly. After living in my home for a few months, I tested the radon gas levels, and they came in at an average reading of 3.2 pCi/l to 3.8 pCi/l, depending on the season. This is pretty close to the EPA action level of 4.0 pCi/l.
Does this imply that the construction of my home's passive radon system was incorrect? No. It means that the emanation of radon gas from the soils below my home is greater than what the passive system can handle. I’m sure there are cold and windy winter days where the average is above 4.0 pCi/l.
The question that begs to be asked is whether a system is working well enough. In my example, the radon measurements are below 4.0 pCi/l, so some may say yes, the system is working as designed. However, some may answer no because the radon average measures pretty close to 4.0 pCi/l. If experience has taught us anything, it’s that even the best-designed and installed passive system may not be adequate to remove radon gas from all homes in Minnesota.
Summary
A passive radon mitigation system does not always guarantee that your home is safe from dangerous radon gas levels, and the only way to accurately determine the radon levels in your home is to have it tested. HomePro Inspections employs the licensed and certified professionals necessary to guarantee accurate radon testing and adherence to all testing protocols.
At HomePro Inspections, our home inspectors are trained to inspect all areas of the home. Your home inspection report documents any issues found and recommends their resolution by you or a qualified professional.
Visit our website to learn more or to schedule your home inspection in the Rochester, Owatonna, and Faribault, MN areas. Contact us today at (507) 202-8942, by email, or by using our convenient online “Schedule Now” feature to schedule an appointment.