Radon · Davidson County

The gas under Nashville.

Davidson County sits in EPA's highest radon category, and the bedrock under Middle Tennessee helps explain why. Here is what the local numbers say and what to do about your house.

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Last updated · sources at the end of the page

Does Nashville have a radon problem?

Davidson County is in EPA Zone 1, the highest-potential category, and in a state screening survey 30% of the 245 Davidson County homes measured read above 4 pCi/L. Nashville Basin geology, with phosphate-rich soils and karst limestone, helps explain it. A short-term test on your lowest lived-in floor is the only way to know your home's level.

What do Davidson County's radon numbers show?

Before EPA drew its 1993 zone map, Tennessee's health department and EPA ran a statewide screening survey using short-term charcoal canisters set out on each home's lowest floor. The U.S. Geological Survey published the county results. For Davidson County:[USGS]

245Davidson County homes measured
30%above EPA's 4 pCi/L action level
64.2pCi/L, the highest reading in the county

The county's average was 5.1 pCi/L, with a median of 2.0 pCi/L, and 5% of homes read above 20 pCi/L.[USGS] That gap between average and median is the story in a nutshell: most homes were modest, a minority were very high, and you can't tell which from the street. USGS itself cautions that the survey was small and focused on population centers, so treat it as a signal, not a forecast.

The zone map that followed put Davidson in Zone 1, meaning a predicted county-average indoor level above 4 pCi/L.[EPA] Statewide, Tennessee's radon program reports that about 1 in 4 homes tested with its free kits come back above 4 pCi/L.[TDEC]

Why is radon high under Nashville?

Radon forms when uranium in soil and rock breaks down, then moves up through the ground and into houses through cracks and openings in the foundation.[EPA] Geologists at the USGS gave the Nashville Basin a high radon potential rating and listed four reasons: elevated uranium readings, abundant phosphate-rich soils, local karst (the cave-and-sinkhole limestone terrain) and generally well-drained soils that let gas travel.[USGS]

"Very high (>20 pCi/L) to extreme indoor radon values (>200 pCi/L) are possible where homes are sited on soils developed on the Chattanooga shale, on phosphate-rich residual soils, or karst pinnacles."U.S. Geological Survey, Tennessee radon assessment (1993)

How should you test a Nashville house?

Start with the free kit

Every Tennessee household can get one free short-term test kit, lab fee included, from the state radon program. Order it online or by phone at 1-800-232-1139.[TDEC]

Set it up right

  • Use the lowest level you actually live in: the finished basement if you use it, otherwise the main floor. Skip kitchens and bathrooms.[EPA]
  • For a 2- to 3-day test, shut windows and outside doors 12 hours ahead and keep them shut, normal comings and goings aside.[EPA]
  • Don't run a short test during a big storm or unusually high winds.[EPA]

Buying or selling?

Real-estate deadlines usually call for a professional test with a documented result. EPA recommends sellers test before listing and fix high levels early, and says saved test and repair records "could be a positive selling point."[EPA]

What if the number comes back high?

EPA's advice: at 4 pCi/L or above, fix the home; between 2 and 4, consider it. If a short-term test read 4 or more, confirm with a second short-term or a long-term test first.[EPA]

The usual fix is a vent pipe and fan that draws radon from under the slab (similar systems work for crawl-space homes) and sends it outside; sealing cracks alone isn't recommended.[EPA] Installation generally takes a day or less.[EPA] Then re-test within 30 days, but not sooner than 24 hours after the system is running, and keep testing at least every two years.[EPA][EPA]

What should it cost? National guides put an installed system at $805–$1,326 (Angi average $1,043), with bigger homes running higher. See the Nashville cost page.

How do nearby counties compare?

EPA radon zones for Davidson and neighboring counties
CountyTownsEPA zone
Davidson CountyNashvilleZone 1 · High
Williamson CountyBrentwood, FranklinZone 1 · High
Wilson CountyMt. Juliet, LebanonZone 1 · High
Rutherford CountyMurfreesboro, SmyrnaZone 1 · High
Sumner CountyHendersonville, GallatinZone 2 · Moderate
Cheatham CountyAshland CityZone 2 · Moderate
Robertson CountySpringfieldZone 2 · Moderate

Zones: EPA radon zone data file, June 2024. EPA says all homes should be tested, whatever the zone.

Keep reading

Sources

  1. USGS Open-File Report 93-292-D: Geologic radon potential, Tennessee chapter (1993)
  2. EPA, Tennessee Map of Radon Zones (PDF)
  3. EPA radon zone data file, June 2024
  4. Tennessee Department of Environment & Conservation, Radon Program
  5. EPA, A Citizen's Guide to Radon (PDF)
  6. EPA, Home Buyer's and Seller's Guide to Radon (PDF)
  7. EPA, Tribal IAQ Resource Directory: Radon
  8. EPA, Consumer's Guide to Radon Reduction (PDF)
  9. Angi, radon mitigation cost (Sep 2026)