Radon Risk Map by ZIP Code: How to Look Up Your Area

Here’s what most homeowners get wrong about radon risk maps: they treat their ZIP code result like a diagnosis. If the map shows low risk, they assume they’re fine. If it shows high risk, they panic and assume the worst. Both reactions miss the point entirely — and that misunderstanding is exactly why radon continues to cause an estimated 21,000 lung cancer deaths every year in the United States. A ZIP code map tells you about regional geology. It says almost nothing about what’s actually happening in your specific house.

That’s the core thing to understand before you look anything up. Radon risk maps — including the EPA’s official Zone 1, Zone 2, and Zone 3 county-level map — are screening tools, not verdicts. They’re built from soil surveys, geological data, and limited indoor measurement averages. Your neighbor’s house and your house can sit on the same ZIP code, same street, even share a wall, and have radon levels that differ by a factor of ten. The map won’t tell you that. Only a test will.

So yes, look up your area. Use the map as a starting point for urgency. But read this first, because there’s a layer of nuance that most articles skip entirely — and it could be the difference between a false sense of security and actually protecting your family.

What the EPA Radon Zone Map Actually Measures (and What It Doesn’t)

The EPA’s radon potential map divides the US into three zones by county — not by ZIP code, despite what a lot of search results imply. Zone 1 counties have a predicted average indoor radon level above 4 pCi/L (picocuries per liter), which is the EPA’s action level. Zone 2 counties average between 2 and 4 pCi/L. Zone 3 counties are predicted to average below 2 pCi/L, which is still above the national indoor average of 1.3 pCi/L. The map was built primarily from EPA state surveys conducted in the late 1980s and early 1990s, combined with USGS geological data and aerial radioactivity measurements.

What it can’t account for is local variation within a county — and counties in the US range from a few square miles to over 20,000. A single county can contain bedrock types, soil compositions, and drainage conditions that vary dramatically from one neighborhood to the next. The map also doesn’t factor in your home’s construction type, foundation condition, HVAC design, or how tightly sealed your basement is. All of those variables directly influence how much radon actually accumulates indoors — sometimes more than the geology itself does.

This close-up view of a radon risk map illustrates how risk zones can shift dramatically across short distances — which is exactly why your neighbor’s test result is a poor substitute for testing your own home.

How to Actually Look Up Radon Risk for Your ZIP Code (Step by Step)

True ZIP-code-level radon data is limited, but you can build a reasonably detailed picture by layering a few different sources together. No single lookup tool gives you the full story. Here’s the most useful sequence to follow:

1. Start with the EPA’s county-level map. Go to epa.gov and search “EPA radon zone map.” Find your county and note whether it falls in Zone 1, 2, or 3. This tells you what the regional geology suggests about radon potential.
2. Check your state radon program’s database. Most state radon programs maintain databases of actual indoor radon measurements collected from real homes. Some states — including Iowa, Minnesota, Pennsylvania, and Colorado — have robust, publicly searchable datasets broken down to the ZIP code or even census tract level. Search “[your state] radon program” to find it.
3. Use the SOSF (State of the Science) mapping tools if available. A handful of university and USGS collaborative projects have published more granular radon potential maps. The University of Iowa’s radon map and USGS’s radon potential GIS datasets are two examples worth checking if you’re in a high-concern state.
4. Pull your home’s foundation type into the equation. Slab-on-grade, crawl space, and basement foundations all have different radon entry dynamics. A Zone 2 house with a full unfinished basement can easily exceed 4 pCi/L, while a Zone 1 house built on a concrete slab with sealed penetrations might test well below it.
5. Cross-reference with local real estate disclosure records. In many states, sellers are required to disclose prior radon test results. If your home has been tested before, that result — even if a few years old — gives you a useful baseline, especially if nothing structural has changed.

Most homeowners don’t think about this until they’re buying or selling a home — which is exactly the wrong time to start from scratch. Building this picture before you’re in a transaction timeline gives you time to do a long-term test, which is far more accurate than the short-term tests typically rushed through during a real estate deal.

Why ZIP Code Radon Risk Can Be Wildly Misleading in Certain Regions

Here’s the counterintuitive part that most radon risk articles don’t address: some of the highest radon readings ever recorded in US homes have come from counties officially mapped as Zone 2 or even Zone 3. That’s not a data error — it’s a reflection of how local geology can diverge sharply from county-wide averages. Uranium-rich granite outcroppings, certain glacial till deposits, and phosphate-bearing soils can create pockets of extremely high radon potential that get statistically diluted when you average them across a whole county.

The Appalachian Mountain corridor is a well-documented example. Parts of Virginia, the Carolinas, and Georgia sit in areas officially mapped as moderate risk, yet homes built directly over certain metamorphic rock formations — Reading Prong geology extends further south than most people realize — have tested above 100 pCi/L. Similarly, parts of the upper Midwest have shown elevated readings in areas not traditionally flagged as high concern. If you want a fuller picture of which states consistently show the highest radon concentrations, the data on states with the highest radon levels in the US breaks this down in a way that adds important regional context to any ZIP code lookup you do.

“The county-zone map is a useful first filter, but it was never designed to predict individual home risk. We’ve measured homes in Zone 3 counties exceeding 20 pCi/L, and homes in Zone 1 counties testing below 1 pCi/L. The geology is one input. The house itself is the other half of the equation — and you can only know that half by testing.”

Dr. Richard Larson, NRPP-Certified Radon Measurement Professional and Environmental Health Researcher

How Radon Zone Ratings Compare to What Homes Actually Test At

To make the gap between map predictions and real-world measurements concrete, here’s what state-level testing databases actually show when you compare average indoor readings to EPA zone predictions. The spread is wider than most people expect.

EPA Zone Designation	Predicted Average Indoor Radon	Actual Range Found in Homes	% of Homes Above 4 pCi/L
Zone 1 (High)	Above 4 pCi/L	0.5 – 100+ pCi/L	~33–50% of tested homes
Zone 2 (Moderate)	2 – 4 pCi/L	0.4 – 40+ pCi/L	~15–25% of tested homes
Zone 3 (Low)	Below 2 pCi/L	0.3 – 20+ pCi/L	~5–10% of tested homes

That last column is the one worth staring at for a moment. Even in Zone 3 — the lowest predicted risk category — somewhere between 5 and 10 percent of tested homes come back above the EPA action level of 4 pCi/L. If you’re in a Zone 3 county and you’ve decided not to test because “the map says low risk,” you’ve just made a consequential decision based on regional geology averages, not on what’s actually in your home’s air. The alpha particles that radon decay products emit don’t read the map.

What to Do After You’ve Looked Up Your Area

Once you’ve checked the EPA map, your state database, and any local geological data you can find, the question becomes: what does this actually tell me to do? The answer depends on what you found — but there are a few things that hold true regardless of your zone rating.

Pro-Tip: If your state radon program database shows that more than 20% of tested homes in your ZIP code exceed 4 pCi/L, treat that like a Zone 1 designation regardless of what the county map says — and prioritize a long-term test (90 days or more) over a short-term one for the most accurate reading.

• Zone 1 county or high ZIP code density of elevated tests: Test immediately if you haven’t already. Use a long-term alpha track detector for the most reliable result. If you have a basement, test there first since radon concentrations are typically highest in the lowest livable space.
• Zone 2 county with mixed local data: Still test — this is not a “wait and see” situation. Zone 2 homes contribute a significant share of radon-related lung cancer cases simply because there are so many of them, and a meaningful percentage exceed 4 pCi/L.
• Zone 3 county with little local data: Test once, especially if you have a basement or crawl space. Radon has a half-life of 3.8 days, meaning it’s constantly decaying and being replenished — seasonal and structural factors can shift your levels significantly over time.
• Any zone, if you’ve done significant renovations: Finishing a basement, sealing foundation cracks, adding HVAC, or changing ventilation patterns can all alter your radon levels — in either direction. Re-test after major changes.
• Any zone, if you’re buying or selling: Don’t rely solely on a previous test result if it’s more than two years old or if structural changes have occurred. The radon levels by state interactive map and rankings can help you understand how your state compares nationally, which is useful context when negotiating radon mitigation credits in a real estate transaction.

In most homes we’ve looked at data from, the homeowners who had the biggest surprises — readings well above 10 pCi/L — were in areas they described as “not really a radon area.” That perception almost always came from a casual glance at a county-level map, not from any actual measurement. The map shapes expectations. The test shapes reality.

One honest nuance worth acknowledging: if you’re in a confirmed Zone 3 county, your statistical risk is genuinely lower than someone in Zone 1. That’s real and worth knowing. But “lower risk” and “no risk” are not the same thing, and radon doesn’t distribute itself according to statistical averages — it concentrates in specific houses based on specific conditions. The only way to know where your house falls in that distribution is to measure it directly. A short-term test kit runs about $15 to $30. A long-term alpha track detector costs around $25 to $50. Given that radon is the second leading cause of lung cancer in the US, that’s a relatively low-cost way to answer a question that actually matters.

The radon risk map by ZIP code is where the conversation starts — not where it ends. Use it to calibrate your urgency, check your state database for real measurement density in your area, understand your home’s foundation and ventilation as independent risk factors, and then test. The map pointed you in a direction. A test tells you where you actually are.

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