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Radon Testing When Buying a House: What It Is and What to Do
Radon is a naturally occurring radioactive gas; EPA action level is 4 pCi/L. The second-leading cause of lung cancer in the U.S. after smoking (EPA). Highest-risk states: Iowa, Minnesota, Wisconsin, Pennsylvania, Colorado, Montana, North Dakota. DIY short-term test kit: $15-$30 (leave in lowest habitable level 48-96 hours). Professional 48-hour electronic test: $100-$200. Above 4 pCi/L: mitigation system $800-$2,500 installed. After mitigation: re-test confirms levels typically below 2 pCi/L. Own Luxury Homes® 12-Point Agent Integrity Audit™.
Radon Testing When Buying a House: What It Is and What to Do
Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It enters homes through foundation cracks and openings. It is colorless, odorless, and tasteless — completely undetectable without a test.
Why Radon Matters in Real Estate
Radon is the second-leading cause of lung cancer in the United States after cigarette smoking, responsible for approximately 21,000 deaths annually according to the EPA. The EPA action level is 4 pCi/L (picocuries per liter of air) — at or above this level, mitigation is strongly recommended. The average indoor radon level in the U.S. is 1.3 pCi/L; the average outdoor level is 0.4 pCi/L. Radon risk is geographic. The U.S. EPA has mapped radon zones based on predicted average indoor radon levels: Zone 1 (highest potential, predicted average above 4 pCi/L) includes much of Iowa, Minnesota, Wisconsin, Michigan, Pennsylvania, Colorado, Montana, North Dakota, and South Dakota. Zone 3 (lowest predicted potential) covers much of the Southeast coast, Gulf states, and Pacific coast. Zone 1 states should prioritize radon testing.
How to Test: DIY vs Professional
DIY short-term test kit ($15-$30): Available at hardware stores and online. A charcoal canister is placed in the lowest habitable level of the home (basement if present, first floor if slab) for 48-96 hours, then mailed to a lab. Results in 1-2 weeks. Limitations: must be conducted in closed-house conditions (windows and doors closed 12 hours before and during the test), and results vary with weather conditions. Professional 48-hour electronic test ($100-$200): A certified radon measurement professional places an electronic continuous monitor. Results are available immediately after the test period, producing a detailed hourly log. Required for most real estate transactions where a professional result is needed for negotiation. Produces a certified report. For real estate due diligence, the professional test is preferred because it produces documentation and is harder for either party to dispute.
What to Do if Radon Is High
Results above 4 pCi/L trigger a recommendation to mitigate. A sub-slab depressurization (SSD) system is the most common mitigation method: a PVC pipe is installed through the slab into the soil layer beneath, connected to a continuously running fan that draws radon-laden air out from under the foundation before it enters the home. Cost: $800-$2,500 installed by a certified radon mitigation contractor. After installation, a retest confirms effectiveness — most systems reduce levels to below 2 pCi/L. The system runs on electricity ($10-$30/year). In a real estate transaction: if testing reveals radon above 4 pCi/L, buyers typically request either a seller-installed mitigation system (with a passing post-mitigation test as a condition of closing) or a closing credit of $1,000-$2,500 to cover the buyer's mitigation cost.
“I have sold homes in high-radon areas where the test came back at 12 pCi/L — three times the EPA action level. The mitigation system cost $1,400. The buyer got a $2,000 credit from the seller, covered the system, and had money left over. That is a great outcome. The alternative — a buyer who skips the radon test, moves in, and finds out two years later the home has elevated radon — is a much more expensive problem with no seller to go back to.”
— Ryan Brown, Principal Broker & CEO, Own Luxury Homes®
Is radon testing required when buying a house?
Radon testing is not universally required by law, but it is strongly recommended in high-risk areas (EPA Zone 1 states including Iowa, Minnesota, Pennsylvania, Colorado, Wisconsin, and much of the northern Midwest). Some states have disclosure requirements for known radon issues. Many buyers in high-risk areas include radon testing as a standard contingency. A $15-$200 test that reveals a $1,000-$2,500 mitigation need is one of the best-ROI inspections available.
What radon level is acceptable in a house?
The EPA recommends taking action when indoor radon levels are 4 pCi/L or above. Levels between 2-4 pCi/L are a gray zone where the EPA recommends considering mitigation. The average U.S. indoor radon level is 1.3 pCi/L. There is no completely safe level of radon — any exposure carries some risk — but levels below 2 pCi/L are generally considered acceptable. After mitigation, most systems reduce levels to below 2 pCi/L.
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— Ryan Brown, Principal Broker & CEO, Own Luxury Homes® (FL License BK3626873)