Imagine for just a moment visiting a busy restaurant kitchen.
Over here, the smell of frying bacon fills the air.
Walk over there and someone chopping onions brings tears to your eyes.
And there, next to the oven, the smell of baking bread.... mmmmm!
Most of us possess an incredibly fine-tuned sense of smell and we can literally follow our noses to the source of a smell, especially a good one!
Radon gas fills spaces in a similar manner, but unfortunately we can't smell it or see it. And unfortunately, in enough concentration, radon can be deadly. The best we can hope to do is detect it, measure it, find its entry point and divert it elsewhere. But finding its entry point can be tricky, and where and when we measure it can be critical.
Factors affecting the way radon fills a space:
• Geography: Some areas are more prone to high radon than others. The EPA map of radon zones shows average test results (red zones being higher) for various zones.
• Topography: Receding glaciers seem to have been responsible for stirring up the soil in many high radon zones. Homes built atop Karst geology or on mountain tops often read high levels of radon.
• Lay of the land the dwelling is sited on: are there partly or completely underground walls?
• Construction details: what is under the foundation? Is a radon mitigation system installed but not in use? Are there open-top cinder block outside walls, and if so, how are they sealed?
• What is the HVAC configuration? Are thermostats manual or programmable? Are there multiple units for different parts of the home? Where do they take in air?
• Air-tightness of the home (airtight drywall—ADA—or caulk and seal—SCS).
Newer homes tend to be much more air-tight, which is great for energy efficiency, but can keep radon trapped with less outside air coming in and fewer places for it to leak out. With a half-life of 3.8 days, the radon trapped in a home will eventually decay, but with a continuous inflow of new radon gas, the sustained concentration can accumulate.
Weather and seasonal variations also play a major role. Several days of a soaking rain can cause radon levels to spike simply by pushing down on the radon gas in the ground surrounding the house, leaving the footprint of the house as the only dry ground for it to escape up through. I have seen radon levels of 2-3 pCi/L spike upwards of 60 pCi/L that lasted 2-3 days during and after a hard rainfall. Snowfall and even high winds can have a similar effect.
Winter months are usually recommended for radon testing because the dwelling is typically much better sealed during winter months. Also, heating systems can produce a “chimney effect,” since heat rises, thus potentially drawing more air up through any openings in the foundation.