Radon Inspection: What to Know
Radon is the #2 cause of lung cancer in the US. It's invisible, odorless, and lives under 1 in 15 American homes above the EPA action level. Here's the 2026 cost, threshold, and mitigation playbook.
Radon-level decision matrix
| Result (pCi/L) | EPA category | 2026 action |
|---|---|---|
| < 2.0 | Low | No action. Retest every 5 years. |
| 2.0 – 3.9 | Elevated | Retest long-term. Consider mitigation if levels persist. |
| 4.0 – 9.9 | Action level | Mitigation strongly recommended. Negotiate credit during contingency. |
| 10.0+ | High | Mitigate before move-in. Don't waive contingency on this finding. |
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Frequently asked
How much does a radon inspection cost?+
Short-term professional radon tests in 2026 cost $150–$300; long-term tests $250–$500. DIY kits run $25–$50 but take 90 days. Mitigation systems, if needed, average $1,200–$2,800 installed.
What is a safe radon level?+
The EPA action threshold is 4.0 pCi/L. Levels of 2.0–3.9 pCi/L warrant retesting and consideration of mitigation. Below 2.0 pCi/L is considered low-risk. There is no truly 'safe' level — radon is the second-leading cause of lung cancer in the US.
Is radon testing required to buy a house?+
Required in some states (e.g. Illinois, Florida disclosure rules), elective in most. Lenders rarely require it. HomeScore recommends a radon test on every basement-level living space and any home in EPA Zone 1 (red zone) — about 40% of US counties.
How long does a radon test take?+
Short-term: 48 hours minimum (closed-house conditions). Long-term: 90+ days. Continuous monitors give hour-by-hour readings during the test window. Schedule early in your inspection contingency — results take 3–7 days to return.
Can high radon kill a real-estate deal?+
Rarely. Mitigation is solvable for $1,200–$2,800 and most sellers will pay for it or credit it at closing. If the seller refuses, request the credit and install post-close — it's a 1-day installation.