Over the years, I’ve found that most skepticism about radon comes not from scientific ignorance but an ignorance of pressure dynamics and building material properties. Since radon is colorless and odorless: many people can’t fathom how much is all around them at any given time (unless they see a cloud chamber). They also tend to think their homes are impenetrable fortresses. That concrete and wood act like radioactive shields. What people don’t realize is that one shield cannot stand up to an army.
Pressure Dynamics
In our industry, some pros joke that “your house sucks”. This isn’t an indictment on your builder—although if they’re not building radon-ready, then maybe it should be—it’s a play on words. Almost every home in North America literally sucks on the soil. Homes build up a negative pressure differential and actively pull radon gas inside to compensate for lost air.
No matter how energy efficient you build a home, you will experience some air loss. This is commonly measured in air changes per hour. Yes that’s right, some homes lose so much air, so frequently, that it’s measured in hours. When air leaves a building, it most often does so at the upper floors. This is a simple convection effect. The same way a hot air balloon works. Hot air rises and leaks out rafters and attics. Supply air must replace this air, but it can’t come from where the air is leaving, so it comes in from lower levels. These lower levels are often in contact with soils or subfloors. Soil air contains radon. Does “your house sucks” make more sense now? This phenomenon is called the stack effect. The effect is exacerbated when the temperature outdoors is vastly lower than indoors (read more on that here).
There exists within the building a neutral pressure plane. Everything above it is “leaky”, everything below is “sucky”. Wind can move this pressure plane into odd shapes. Confounding contractors and radon scientists (read more here).
Energy-efficient builders are aware of this fact and aim to control airflow. They will include supply air ducts and seek to control where and how the supply air enters the home. This is where air exchangers can keep efficiency very high. Air exchangers heat-treat inbound air so that HVAC systems do not have to work as hard. In rare instances, they can be used to control radon (read more on that here). Although this usually isn’t the most efficient way to lower radon levels, it works when all other methods have failed.
Radon Particle Size: why you can’t block it out
Radon is an element. That means it’s one of the smallest things in our universe. Its atomic weight is 86. To create fabrics, paints, plastic sheets, and other man-made barriers that can block it is just not feasible. Heck, even scientists detecting dark matter in the worlds’ most advanced laboratories cannot block radon. They have to find other ways to remove the contaminant from their experiments.
A major part of airflow control is blocking out all unwanted air intake and exhaust. If you control 100% of the supply air, and are intelligent enough to take it from outdoors and not the soil, then you should be able to get rid of 100% of the radon. The problem is: those efficiencies aren’t feasible in the real world. All homes leak some air and all foundation types suck some air.
This is why if you see a product that claims to “block” radon, it’s almost always snake oil. If you think you’ve found one with real data, please contact me, as I want to sell it. However, in my career, every radon blocker I’ve seen advertised has been ignorant–at best–and ethically disgusting–at worst.
New homes versus old homes
Many homeowners believe that new homes have less radon than older homes. This is an assumption without merit. Many experienced radon testing and mitigation professionals hypothesize that newer homes may actually have higher radon levels. Typically new homes will be more air tight, so you would think that the stack effect would be lessened, right? However, air loss that builders cannot control, combined with stronger HVAC blower units, may end up “sucking” on the soil harder. You see: since windows, doors, and insulation have gotten better at containing air, then the replacement air is more likely to come from the soil or subfloor. Older homes are draftier as well, which means more of their make up air may come from walls, windows, and doors, rather than porous concrete or crawlspaces.
Again, this is a hypothesis and should be tested. If you’re interested in conducting an experiment please contact me.
Passive radon systems biggest flaw: don’t drop the ball
Many newer homes are built with “passive” radon systems. Passive radon systems–even when built properly–rarely work 365 days a year, so you still need to test and add a fan. This is a huge misconception that I hear every single day: it wears on me because I know it’s putting people at risk. Well-intentioned engineers and builders using dated terminology are turning homeowners away from testing. This term implies the system works passively all the time. It gives a false
sense of security and leads to many homeowners still being at risk. It’s analogous to the premature NFL end-zone celebration where a player drops the football one yard before the goal line. Be sure to build radon ready to a contemporary radon standard (ANSI-AARST) and make sure that all RRNC passive homes are tested for radon once complete.
Construction type, home age, and radon “blocking” tools: none of these materials or methods can 100% guarantee you’ll have no radon. Repeated testing and system maintenance is the best way to limit your exposure. For help designing a radon ready home, click here and contact an NRPP certified pro.
Regardless of your home’s age and built type, it’s best to perform long term radon testing often. The EPA recommends testing all US homes once every five years in the winter. Those with systems need to test every two. Read my full maintenance recommendations here.
In the future, you may be able to check your radon exposure from toenail clippings. Yikes, I’d rather keep it out in the first place.
Thanks for reading!
Post Categories
Test for radon order an at - home radon test kit
The EPA recommends performing a radon test on every American home at least once every five years. If you have an existing radon system, EPA recommends testing every two. Sign up for PDS Protects (™) and let us send your kits on schedule so you don’t forget!