EPA Radon Zones Explained: What Homebuyers Need to Know

Radon is the second leading cause of lung cancer in the United States, responsible for roughly 21,000 deaths per year according to the EPA. It is an odorless, colorless gas that seeps into homes from naturally occurring uranium in soil and rock. If you are buying a home, understanding your property's radon zone is one of the cheapest, highest-impact due diligence steps you can take.

The EPA divides the entire US into three radon zones based on predicted average indoor screening levels. Here is what each zone means for you as a buyer, what testing costs, and what to do if levels are high.

The Three EPA Radon Zones

The EPA's Map of Radon Zones classifies every US county into one of three zones based on indoor radon potential. The classification is based on geological data, indoor radon measurements, and building characteristics.

The critical threshold is 4 pCi/L (picocuries per liter). The EPA recommends mitigation at or above this level. The World Health Organization sets a stricter reference level of 2.7 pCi/L (100 Bq/m3). For context, outdoor air typically measures 0.4 pCi/L.

Zone designations are county-level averages. A home in a Zone 3 county can still have dangerously high radon levels due to localized geology. The EPA is clear: every home should be tested regardless of zone.

Which States Have the Highest Radon Risk?

States with the most Zone 1 counties include Iowa (where virtually every county is Zone 1), Minnesota, Pennsylvania, Ohio, Colorado, and Nebraska. The northern Midwest and Appalachian regions have the highest concentrations of Zone 1 counties due to glacial deposits and granite bedrock.

But geography alone does not determine your home's radon level. Foundation type, soil permeability, HVAC design, and even seasonal weather all influence how much radon accumulates indoors. A slab-on-grade home next door to a basement home can have dramatically different readings.

Testing: Costs and Methods

Radon testing is one of the most affordable environmental checks you can do. Here is what to expect:

For real estate transactions, most buyers use a professional short-term test with a CRM. These devices log hourly readings and produce tamper-evident reports, which gives both parties confidence in the results. Many states require certified testers for real estate transactions.

You can order a DIY test kit from the EPA's list of radon testing resources or through your state radon program. Some states offer free or discounted kits.

Mitigation: Fixing High Radon Levels

If your test returns 4 pCi/L or above, mitigation is straightforward. The most common approach is sub-slab depressurization (SSD): a contractor drills a hole through your basement floor, installs PVC piping and a fan, and vents radon gas above the roofline. Typical costs:

• Standard SSD system: $800 – $1,500 for most homes
• Complex installations (crawlspace, multiple foundation types): $1,500 – $2,500
• Radon-resistant new construction (RRNC): $350 – $500 added during building

SSD systems reduce radon levels by up to 99% according to the EPA's Consumer's Guide to Radon Reduction. Annual operating cost is minimal (fan electricity runs $50-$100/year). Systems last 15-25 years with occasional fan replacement ($200-$400).

What This Means for Homebuyers

Radon should never be a deal-breaker. It should be a negotiation point. A $150 test and an $800-$2,500 mitigation system are trivial compared to the cost of a home. Here is a practical approach:

1. Check the zone first. Know whether your target property is in Zone 1, 2, or 3 before you even visit.
2. Always test during inspection period. Do not skip this because the home "looks fine" or is new construction.
3. Negotiate credits for mitigation. If radon is above 4 pCi/L, ask the seller to install an SSD system or provide a credit of $1,500-$2,500.
4. Retest after mitigation. Confirm levels dropped below 4 pCi/L (ideally below 2 pCi/L).
5. Retest every 2-5 years. Levels can change over time as soil conditions shift.

According to the CDC, radon exposure is the number one cause of lung cancer among non-smokers. For smokers, radon and tobacco together create a risk that is far greater than either alone. Testing is cheap insurance.