Blog › 2026-10-21
Is Radon a Problem in Greenville County, SC?
Short answer: Greenville County has the highest radon potential rating EPA gives. In EPA's Map of Radon Zones, it is listed as Zone 1, and it is the only county in South Carolina with that rating. That doesn't mean every house here has high radon. It does mean every house here should be tested.
What we checked
We didn't rely on secondhand claims. We pulled EPA's own published county data (the "Radon Zones" data file linked from EPA's Map of Radon Zones page) and looked up every South Carolina county. Here's what it shows for the Upstate:
| County | EPA radon zone | Upstate towns in it |
|---|---|---|
| Greenville | Zone 1 (highest potential) | Greenville, Simpsonville, Mauldin, Taylors, Travelers Rest, Fountain Inn, most of Greer |
| Spartanburg | Zone 2 (moderate) | Spartanburg, part of Greer |
| Pickens | Zone 2 (moderate) | Most of Easley |
| Anderson | Zone 2 (moderate) | Anderson, part of Easley's outskirts |
| Laurens | Zone 2 (moderate) | South of Fountain Inn |
Source: EPA radon zones county data (2024 file). Town-to-county notes are general geography; some cities cross county lines.
What the zones actually mean
EPA and the U.S. Geological Survey built the map in 1993 using indoor radon measurements, geology, aerial radioactivity, soil data and foundation types. Each county got one of three ratings:
- Zone 1: predicted average indoor screening level greater than 4 pCi/L.
- Zone 2: predicted average between 2 and 4 pCi/L.
- Zone 3: predicted average below 2 pCi/L.
Those are county-wide predictions of a short-term "screening" average, not a measurement of any home. EPA says plainly that the map should not be used to decide whether an individual home needs testing, because homes with elevated radon have been found in all three zones.
Why the Upstate rates higher than the rest of the state
Radon comes from the natural decay of uranium in soil and rock. The Upstate sits in the Piedmont, close to the Blue Ridge, where much of the ground is weathered crystalline rock like granite and gneiss rather than the sandy coastal-plain sediments found across much of the Midlands and Lowcountry. USGS's geologic radon assessment of South Carolina (Open-File Report 93-292-D, which EPA recommends reading alongside the map) is the place to go for the detailed geology. The practical result shows up in the map itself: the higher-rated counties cluster in the northwest corner of the state.
Geology is only part of it. How much radon ends up inside depends on the individual house: cracks and openings in the foundation, whether it sits on a basement, slab or crawlspace, how tightly it's built, and how the HVAC system moves air. Two houses on the same street can test very differently.
Local building codes have noticed too
The International Residential Code includes an optional appendix on radon-resistant construction that points jurisdictions to EPA's Zone 1 list. A 2021 Greenville County building codes memo to County Council noted Greenville County's listing as a "High Radon-Potential" (Zone 1) county in that appendix. If you're building new, ask your builder whether radon-resistant features such as a gas-permeable layer, vapor barrier and a stubbed-out vent pipe are included, and test after move-in either way.
So what should a Greenville homeowner do?
- Test. It's quick and inexpensive. See how to test your Greenville home for radon, or book professional radon testing.
- Read the number against EPA guidance. Fix the home at 4 pCi/L or higher. Consider fixing between 2 and 4 pCi/L.
- If it's high, mitigate. A radon mitigation system is usually a one-day install. Then retest to confirm.
- Retest over time. EPA suggests retesting every two years and after major renovations, even if the result was low.
Living outside Greenville County, in Spartanburg, Easley or Anderson? Zone 2 still means a predicted average between 2 and 4 pCi/L, which is in EPA's "consider fixing" range. The advice is the same: test.
More from EPA: EPA Map of Radon Zones and supplemental information. South Carolina's state radon program is run by the SC Department of Environmental Services (800-768-0362).
Quick answers
What EPA radon zone is Greenville County, SC?
Zone 1, EPA's highest-potential rating. It is the only South Carolina county in Zone 1, according to EPA's county radon zone data.
Does Zone 1 mean my house has high radon?
No. The zone is a county-level prediction. EPA says homes with elevated radon are found in all zones, so only a test can tell you about your home.