Guilford County Is Low-Risk for Radon. Your House Might Not Be.

A Pennsylvania builder from one of the country’s highest radon zones explains what the EPA map misses, and how Greensboro homeowners can test for free.

Quick Answer: The EPA puts Guilford County in Radon Zone 3, the lowest of its three risk tiers. That rating predicts a county-wide average, not the level inside any one home. North Carolina’s own health department reports elevated radon in 90 of the state’s 100 counties, and the EPA says every home should be tested regardless of zone. The state has given away free test kits every January for years, so finding out may not cost you anything.

If you’ve ever looked up radon for Greensboro, you probably found a map, saw Guilford County shaded in the lowest-risk color, and closed the tab. Most people do. I’d ask you to give me five minutes before you close it for good.

I live in York County, Pennsylvania, which is on the opposite end of that map. We’re EPA Zone 1. State testing data shows basement averages near 10 pCi/L in some York ZIP codes, well over the EPA’s action level of 4.0, and roughly a third of homes here test above that line. I spent my working life building houses in York, so radon was something I dealt with on every job. Living in a high-radon area taught me what the zone map is good for and what it isn’t.

The map was never meant to judge your house

The EPA Map of Radon Zones sorts every county in the country into three tiers. Zone 1 counties have a predicted average indoor level above 4 pCi/L, Zone 2 falls between 2 and 4, and Zone 3, which includes Guilford, is predicted to average below 2.

The EPA is clear about the map’s purpose. It exists to help government agencies decide where to spend their resources and where to adopt radon-resistant building codes. The agency says outright that it shouldn’t be used to decide whether a particular home gets tested, that elevated homes have been found in all three zones, and that all homes should be tested.

An average works the same way on your street as it does in a spreadsheet. If most of the houses around you sit at 1 pCi/L and one sits at 9, the average barely moves. The family in that house is still breathing a 9.

North Carolina’s own numbers tell a different story

The zone map was drawn up in the early 1990s from the data available then. North Carolina’s Department of Health and Human Services has been collecting newer test results, and in late 2025 it reported elevated radon in 90 of the state’s 100 counties. The department also estimates that about 480 North Carolinians die from radon-related lung cancer every year, and it calls radon the state’s leading environmental cause of lung cancer.

None of that means your house has a problem. It means a county label isn’t enough to decide either way.

Why two houses on the same street can test differently

This is where my builder’s background comes in, because the house matters more than the ZIP code.

Radon comes up out of the soil and finds its way inside through the foundation: slab cracks, wall joints, sump pits, the gaps around plumbing, and open dirt in a crawl space. How much gets in depends on the soil directly under the house and how the house was built and sealed.

Then there’s the stack effect. A heated house acts like a chimney. Warm air rises and leaks out near the roof, and replacement air gets pulled in low, right where the soil gas is waiting. That’s why readings tend to climb in the colder months, when the furnace is running and the windows stay shut. Tight, energy-efficient construction adds to it, because whatever gets in has a harder time getting back out.

Two houses built from the same plans a few lots apart can sit on different pockets of soil, settle differently, and get finished differently over the years. A neighbor’s result tells you about the neighbor’s house. So does a test from before you finished the basement or closed in the porch.

A Guilford County detail worth knowing: well water

If you’re on a private well, pay attention to this section.

A U.S. Geological Survey study sampled 70 wells across Guilford County and found radon in the water ranging from 37 to 6,300 pCi/L, with a median of 735. The highest readings came from the granite formations in the northwestern part of the county, and levels ran lower in the central and southern areas. The study is from 1997, so treat it as a reason to ask questions, not as a current reading for your property.

The USGS also found that drinking the water carries less risk than breathing radon in indoor air. The larger concern is what happens when water runs, because showers, dishwashers and washing machines release radon into the air you breathe. If you’re on a well, ask your water tester about radon by name. It usually isn’t part of a standard test.

How to find out, possibly for free

Every January is National Radon Action Month, and North Carolina has used it to give away free home test kits for several years running. In 2026 the state offered 8,000 of them at radon.ncdhhs.gov, one per household, with postage and lab analysis included. They went first come, first served, so it’s worth checking that site on New Year’s Day.

Outside January, a short-term kit from a hardware store or online runs about $15 to $50. Set it on the lowest level of the house that you actually live in, keep windows and doors closed as much as you can, leave it out for the time the package says, and mail it to the lab.

If the result comes back under 4.0 pCi/L, retest every couple of years and after any major renovation. If it comes back at 4.0 or higher, run a second test to confirm before you call anyone.

If you need a fix, you’ll have to vet the contractor yourself

This is where North Carolina and Pennsylvania differ in a way that matters.

In Pennsylvania, anyone who tests for or mitigates radon has to be certified by the state Department of Environmental Protection, and that’s been the law since 1988. North Carolina doesn’t license radon contractors. The NC Radon Program recommends hiring someone certified through one of two national programs, the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB). Nobody at the state level checks that for you.

Vetting contractors is most of what I do now. I founded York PA Radon Pros to check out the companies that do this work in my area, because homeowners kept telling me they didn’t know who to trust. The questions I ask work anywhere:

• Can you show me your NRPP or NRSB certification number? Look it up yourself on the program’s website.
• Will you inspect the house in person before you quote? A price given over the phone is a guess.
• Does your price include a follow-up test after the system is running? That test is how you know the system worked.
• What does the fan cost to replace, and who do I call when it quits? Fans wear out eventually, and you want an answer before you sign.

A good contractor answers those without getting defensive. If money is the obstacle, the state has pointed homeowners toward assistance through the North Carolina Housing Finance Agency.

Let the test answer the question

I’m not writing to scare anybody in Greensboro. The odds are decent that your house is fine. But you won’t know that from a county map. A test kit, which may be free this January, will tell you.

Tom Bartokowski is the founder of York PA Radon Pros and the owner of Bartokowski Builders in York, Pennsylvania. He does not perform radon testing or mitigation. He vets the companies that do.