Guilford County's EPA zone classification might be giving homeowners a false sense of security. Here's what the actual NC data shows about radon risk in Greensboro and High Point.
If you’ve looked into radon at all, you’ve probably come across the EPA’s zone map and noticed that Guilford County falls into Zone 3 — the lowest predicted risk category. It’s easy to read that and move on, assuming your home is fine. A lot of homeowners do exactly that.
But the NC Department of Health and Human Services publishes its own county-level data, and what it shows about Guilford County is worth understanding before you draw any conclusions. The EPA zone is a population-level estimate. Your home is not a population average. Here’s what that distinction actually means — and why it matters more in the Piedmont than most people realize.
Radon testing is simpler than most people expect. We place a continuous electronic radon monitor in the lowest livable area of your home — at least 20 inches off the floor, away from drafts and high-humidity zones. The monitor runs for a minimum of 48 hours under closed-building conditions, meaning exterior windows and doors stay shut throughout. Your HVAC system can operate normally.
At the end of the test, you get a formal report that includes the average radon level recorded, equipment calibration documentation, and chain-of-custody records. That last part matters a great deal if you’re buying or selling a home — real estate transactions in North Carolina require certified, documented results from a qualified professional. A $15 kit from the hardware store won’t satisfy that requirement.
Radon forms naturally from the radioactive decay of uranium in soil and rock. It’s a gas, so it moves — rising up through the ground and finding its way into your home through any opening where the structure meets the earth. Foundation cracks, gaps around pipes, sump pump openings, construction joints. In a tightly sealed home, especially in winter, it accumulates.
Here’s what makes this particularly relevant for Guilford County: a significant portion of homes in Greensboro and High Point were built with crawl space foundations. That’s not a minor detail. A crawl space creates a large, often open interface between the soil beneath your home and the air inside it. Radon doesn’t need a dramatic pathway — it seeps through the soil, rises into the crawl space, and migrates upward into the rooms where your family spends time.
This is different from a basement slab situation, where the contact point is more defined and more easily sealed. A crawl space — especially one that isn’t properly encapsulated — gives radon a wide-open channel. We’ve been working in Guilford County crawl spaces for over 30 years, and we see this dynamic play out regularly. The homes that test elevated aren’t always the ones you’d expect. They’re often mid-century neighborhoods in Greensboro — areas with older construction, original crawl spaces, and no vapor barrier to speak of.
The Piedmont’s geology adds another layer to this. A 1997 USGS study of Guilford County found radon in local groundwater ranging from 37 to 6,300 pCi/L, with a median of 735 pCi/L. The highest concentrations were found in younger granites in the northwestern portion of the county. That kind of geological variability means radon risk isn’t uniform across Guilford County — it shifts by neighborhood, by soil type, by the specific rock formations beneath a given address. No zone map resolves that for an individual home. Only a test does.
The EPA’s radon zone map divides counties into three categories based on predicted average indoor screening levels. Zone 1 counties are predicted to average above 4 pCi/L. Zone 3 counties — where Guilford County sits — are predicted to average below 2 pCi/L. That sounds reassuring. The problem is that “predicted average” is doing a lot of work in that sentence.
The EPA zone is a statistical estimate based on geology, housing characteristics, and limited screening data. It predicts what a large group of homes in a county might average. It says nothing about what any specific home will measure. And the NC DHHS county-level radon map — which tracks actual test results, not predictions — shows Guilford County in red. That means at least one home in this county has tested at or above 4 pCi/L, the EPA’s action level. In practice, it means more than one.
NC’s Division of Public Health is direct about this: the Piedmont and mountain counties are estimated to have the greatest proportion of homes with elevated radon levels in the state. That’s a meaningful statement for anyone in Guilford County who has been treating Zone 3 as a clean bill of health.
The NC DHHS recommends that all homes in North Carolina be tested regardless of county zone classification. Radon is the number one environmental cause of lung cancer in this state, responsible for an estimated 480 deaths per year. It has no smell, no color, no taste. The only way to know your home’s level is to measure it. A zone map — even a well-constructed one — cannot do that for you.
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If you’re buying or selling a home in Greensboro or High Point, radon testing isn’t just a good idea — it’s part of the transaction process. Under NC General Statutes §47E, sellers are required to disclose known environmental hazards, and NC real estate brokers are obligated to disclose if radon levels meet or exceed 4 pCi/L to all parties involved.
That disclosure requirement creates a practical question: when do you want to find out? Discovering elevated radon during a buyer’s due diligence period, under deadline pressure, is a harder situation than knowing in advance. Sellers who test before listing have the option to address the issue proactively — which puts them in a much better position than having it surface as a surprise during negotiations.
The short answer is that they’re not accepted. Real estate transactions in North Carolina require certified, documented test results from a qualified professional. A passive charcoal kit from a hardware store doesn’t come with calibration records, chain-of-custody documentation, or a formal report — and buyers, agents, and lenders won’t treat it as valid evidence of a home’s radon levels.
There’s also a practical accuracy gap. DIY kits are passive devices. They absorb radon over time and get mailed to a lab for analysis. A professional continuous electronic monitor records radon levels hour by hour throughout the test period, giving a much clearer picture of how levels fluctuate and what the true average is. A single spike in a passive kit’s result looks the same as a sustained elevated average — which can lead to unnecessary alarm or, in the other direction, a misleadingly low reading if the spike happened to fall outside the collection window.
Beyond the real estate context, there’s the matter of what you do with the results. If your home tests above 4 pCi/L, the next question is: what’s driving it, and how do you address it? We bring 30 years of crawl space and indoor air quality experience to that conversation. We can look at your crawl space conditions, your vapor barrier situation, your foundation type, and give you a grounded assessment of where the radon is likely entering and what options make sense — not just a reading on a piece of paper.
**Does radon testing cover the whole house, or just one area?**
The standard protocol places the monitor in the lowest livable area of the home — typically the ground floor or, if there’s a finished basement, in that space. That’s where radon concentrations are highest, since it enters from below and dilutes as it moves upward. If you have a finished basement you use regularly, that’s where the test should be centered.
**How long does a radon test take?**
The minimum for a short-term test is 48 hours. During that window, closed-building conditions apply — exterior windows and doors stay shut, though your HVAC system can run normally. Results are typically available shortly after the monitor is retrieved and the data is processed.
**Is Guilford County actually at risk, or is this overblown?**
It’s a fair question, and the Zone 3 classification makes it easy to assume the answer is no. But as we’ve covered above, Zone 3 reflects a population average — not a per-home prediction. The NC DHHS county map shows confirmed tests above the EPA action level in Guilford County. The Piedmont’s geology creates real variability within the county. The NC Division of Public Health specifically calls out Piedmont counties as having among the highest proportion of homes with elevated radon in the state. Whether your specific home in Greensboro, High Point, or elsewhere in Guilford County is a problem or not, you genuinely don’t know until you test it.
**What happens if my test comes back high?**
Elevated radon is a fixable problem. Mitigation systems — typically sub-slab or sub-membrane depressurization — can dramatically reduce indoor levels. The important thing is knowing your starting point. A professional test gives you that, along with documentation you can act on.
**Is a home air quality test the same as a radon test?**
Not exactly. A home air quality test is a broader category that can include testing for mold, VOCs, particulates, humidity, and other contaminants in addition to radon. Radon testing is one specific component of that picture. At Clean Air LLC, radon testing fits within a broader indoor air quality framework that also covers crawl space conditions, moisture control, and duct system health — all of which affect what you’re breathing inside your home.
If you’ve been holding off because you figured Zone 3 meant your home was low-risk, the data suggests it’s worth revisiting that assumption. Guilford County has confirmed elevated test results. The Piedmont geology creates real within-county variation. And the most common foundation type in Greensboro and High Point — the crawl space — happens to be the most common radon entry pathway in this region.
Testing is the only way to know what’s actually happening in your specific home. Everything else is a guess based on averages that may not apply to your address, your foundation, or the soil beneath your property.
If you’re buying or selling, the timeline matters — getting a certified test done before the due diligence clock starts ticking puts you in a much better position. If you’re a homeowner with no immediate transaction in mind, the answer is still the same: the test is the starting point for every decision that follows.
We’ve been working in Guilford County homes since the early 1990s. If you have questions about radon testing or want to understand what the results might mean for your crawl space or overall indoor air quality, reach out and we’ll walk you through it.
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