What is Radon Testing in Real Estate?
Radon testing measures the concentration of radon gas inside a building. Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It seeps into buildings through cracks in foundations, gaps around pipes, and other openings. Radon is colorless, odorless, and the second leading cause of lung cancer in the United States after smoking, responsible for an estimated 21,000 deaths annually.
The EPA recommends radon testing for all real estate transactions. The action level is 4.0 picocuries per liter (pCi/L). Homes testing at or above this level should be mitigated. Approximately 1 in 15 homes in the U.S. has elevated radon levels, though prevalence varies significantly by geography. The Midwest and Mountain West tend to have higher radon levels than coastal areas.
How radon testing works
Short-term tests (2-7 days) use charcoal canisters or continuous electronic monitors placed in the lowest livable area of the home. These are the standard tests used during real estate transactions. They provide a snapshot of radon levels during the test period.
Long-term tests (90+ days) provide more accurate averages since radon levels fluctuate seasonally. These are used for post-mitigation monitoring or when short-term results are borderline.
Professional radon testing costs $150-$300. DIY test kits are available for $15-$30 at hardware stores but are less reliable and not typically accepted in real estate transactions.
Radon mitigation
If testing reveals elevated levels, a radon mitigation system can reduce concentrations by up to 99%. The most common system is sub-slab depressurization, which involves installing a pipe through the foundation slab connected to a fan that draws radon from beneath the foundation and vents it above the roofline. Installation costs $800-$2,500 depending on home size and foundation type.
Radon in real estate transactions
Radon testing is typically ordered by the buyer during the inspection period alongside the general home inspection. If elevated levels are found, the buyer can negotiate for the seller to install mitigation, request a price reduction to cover mitigation costs, or terminate the contract if the contingency allows. For investors, radon mitigation is a relatively inexpensive fix that should be factored into repair estimates rather than used as a deal-killer.