By Samuel 
It is also an easy way to talk yourself out of a test your own house may need.
Radon does not spread evenly down a street. Two homes on the same block can return very different results, because each one pulls gas from the soil directly beneath it.
That is why DocAir, the Nashville building science firm Barry Westbrook founded in 2002, will not recommend radon mitigation off anyone’s numbers but yours.
Westbrook is a Senior Certified Industrial Hygienist, and the firm’s rule is short. Measure the house you actually live in, then decide.
Radon Rises From the Soil Under Your Own Floor
Radon is a radioactive gas that forms as uranium in soil naturally breaks down. It drifts upward into whatever building happens to sit on top.
Metro Nashville’s health department lists the ways in. Cracks in floors and walls, gaps in suspended floors and around pipes, hollow wall cavities, and construction joints.
None of those openings are shared with the house next door. Your slab, your crawl space, and your pipe penetrations belong to your house alone.
So does the patch of ground under them. That single fact is why a neighbor’s result can’t stand in for yours.
Why Two Houses on One Street Test So Differently
EPA’s buyer and seller guide is direct bout it. Homes right next to each other can have different indoor radon levels, so a neighbor’s result can’t estimate yours.
Here is what drives the gap.
The ground changes lot to lot. EPA names local geology as one of the factors behind a home’s radon level. Geology does not follow property lines.
Foundations let gas in differently. A slab, a basement, and a crawl space each give soil gas a different route inside. That is why DocAir designs every system around the foundation type.
Every house has its own openings. Cracks in solid floors, construction joints, gaps around service pipes. Two crews building side by side leave two different sets of holes.
Pressure inside the house pulls on the soil. A home running slightly negative draws soil gas up through whatever gaps it has.
In crawl space homes, DocAir frequently traces high readings back to leaky ductwork and ventilation problems that create exactly that pull.
That finding changes the fix. When ducts are the main driver, DocAir says sealing them may lower radon without a full fan system.
How the house is lived in. Major renovations can change radon levels, and EPA says to test again once the work is done.
Metro Health also warns that radon exposure climbs in winter, when doors and storm windows stay shut and ventilation drops.
Why Middle Tennessee Homes Are Worth Testing
The stakes are real. The U.S. Surgeon General has warned that radon is the second leading cause of lung cancer in the United States.
EPA lists Davidson County as an area with high potential for elevated radon. Local testing backs that up.
The other 60 percent or so did not. A clean result next door and a high one in your living room are both ordinary outcomes on the same block.
Metro Health’s page backs that reading. Testing by the department and others found wide-ranging radon levels among homes in all areas of the county.
Live outside Davidson County? The advice holds.
EPA says every home should be tested regardless of zone, because elevated levels have been found in all three of its radon zones.
How to Get a Radon Number You Can Trust
A result is only as good as the test behind it. EPA’s testing guidance comes down to a few habits.
- Test the lowest lived-in level. That means the basement if your family uses it; otherwise, the first floor. Skip the kitchen and bathrooms.
- Place the device with care. Keep it at least 20 inches off the floor, away from drafts, high heat, humidity, and exterior walls.
- Give it enough time. Short-term tests should run at least 48 hours. For a 2- or 3-day test, close windows and outside doors 12 hours before it starts and keep them shut throughout.
- Go long when you can. A long-term test stays in place more than 90 days and is more likely to reflect your year-round average.
DocAir places calibrated monitors for at least 48 hours and also offers 90-day long-term measurement, depending on what the homeowner needs to decide.
What to Do With the Number You Get
EPA’s action level is 4 picocuries per liter (pCi/L). At or above it, fix the home. Between 2 and 4, EPA says consider fixing.
A short-term result of 4 or higher calls for a follow-up test first. A second short-term test is the fast route, and a long-term test gives the fuller picture.
This is where science before sales earns its keep. DocAir will not recommend mitigation when a properly run test comes back below EPA’s action level.
When the numbers do call for a fix, Westbrook reviews the property as a complete system before any mitigation plan is specified.
Every engagement is documented with before-and-after radon readings in a written findings report the owner keeps.
So thank your neighbor for the tip, then test your own house. Their number describes the soil directly beneath their home, not yours.