Radon is invisible, odorless, and tasteless. It causes no immediate physical symptoms. And it is the second leading cause of lung cancer in the United States, responsible for an estimated 21,000 deaths every year — more than drunk driving. In the Portland metro area and Southwest Washington, approximately 1 in 4 homes tests at or above the EPA action level. Your home may have a radon problem and you would have no way of knowing without testing.
If your home inspection report recommended radon testing, or if testing was conducted and came back elevated, this article will give you a complete picture of what you are dealing with and what to do about it.
What Is Radon and Where Does It Come From?
Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It is present everywhere in the earth’s crust, and low background levels exist in virtually all outdoor air. The problem occurs when radon migrates from the soil into enclosed spaces — homes, schools, workplaces — where it accumulates to concentrations that pose a meaningful health risk.
Radon enters homes primarily through the path of least resistance from the soil below: foundation cracks, gaps around pipes and utility penetrations, hollow block foundation walls, sump pump openings, and the general interface between soil and the lowest level of the structure. In homes with crawl spaces — extremely common in the Portland area — radon can accumulate in the crawl space and migrate upward into the living area through the floor system.
Because radon is heavier than air, it tends to accumulate at the lowest levels first — basements, ground-floor rooms, and areas directly above crawl spaces. This is why radon testing protocols specify testing at the lowest livable level of the home.
Why the Portland Area Has Elevated Risk
The Pacific Northwest’s geology contributes significantly to its radon risk profile. The Columbia River Basalt Group — the volcanic rock formation underlying much of the Portland metro area and extending into Southwest Washington — contains elevated uranium concentrations relative to national averages. As this rock weathers and breaks down, it releases radon into the overlying soil, which then migrates into buildings.
Multnomah, Washington, Clackamas, and Clark counties all have documented histories of elevated radon in residential testing. Portland Public Schools testing found elevated levels in more than 120 classrooms. There is no neighborhood within the metro area that can be considered automatically safe — testing is the only reliable way to know the levels in any specific home.
The Health Risk: What the Numbers Mean
Radon itself does not directly cause cancer. It decays into radioactive daughter products — polonium, bismuth, and lead isotopes — that are electrically charged, adhere to airborne particles, and are inhaled into the lungs. These decay products emit alpha radiation that damages lung cell DNA, and repeated exposure over years increases the probability of lung cancer.
The risk is cumulative and dose-dependent. The EPA estimates that at 4 pCi/L — the action level — the lifetime lung cancer risk is approximately 7 per 1,000 non-smokers and 62 per 1,000 smokers. At 8 pCi/L, those numbers roughly double. These are real, statistically meaningful increases in cancer risk for everyone living in the home.
The interaction between radon and smoking is particularly significant — the two act synergistically, and the combined risk for a smoker in a high-radon home is far greater than the sum of the individual risks. Children are also at elevated risk because they breathe faster than adults, have more rapidly dividing cells, and will accumulate longer lifetime exposures if they grow up in a high-radon environment.
Understanding Radon Test Results
Radon is measured in picocuries per liter (pCi/L). Outdoor air typically averages around 0.4 pCi/L. The EPA action level is 4 pCi/L, at which mitigation is strongly recommended. The EPA also notes that levels between 2 and 4 pCi/L should be considered for mitigation, particularly if occupants smoke or children are present.
Short-term tests (48–96 hours, using charcoal canisters) are the most common method during real estate transactions because results are available quickly. They provide a reasonable snapshot but are subject to variation based on weather, season, and whether testing protocols were properly followed. Long-term tests (90 days or more, using alpha track detectors) provide a more accurate picture of average annual exposure and are recommended for definitive assessment.
Radon levels are typically higher in winter than summer — homes are more tightly sealed, and the temperature gradient between indoor and outdoor air is greater, increasing the stack effect that draws soil gases upward. A short-term test conducted in summer may underestimate average annual exposure.
Radon Mitigation: What the Fix Actually Looks Like
Radon is one of the more straightforwardly solvable environmental hazards in residential construction. Active Soil Depressurization (ASD) — the standard mitigation approach — is effective in the vast majority of homes, typically reducing radon levels by 50 to 99 percent.
The system works by creating a low-pressure zone beneath the foundation slab or crawl space vapor barrier that intercepts radon before it enters the home and vents it harmlessly to the exterior. The components are simple: a suction pit beneath the slab (or under the crawl space vapor barrier), PVC piping routed to the exterior, and a continuously running in-line fan that maintains the pressure differential. The fan runs constantly and quietly, consuming roughly as much electricity as a light bulb.
For homes with crawl spaces — common in the Portland area — mitigation typically involves sealing and covering the crawl space floor with a heavy-gauge vapor barrier and installing the suction point beneath it. This is often combined with crawl space encapsulation work that provides moisture management benefits beyond radon reduction.
Radon mitigation systems installed by certified contractors in the Portland area typically cost between $800 and $2,500 depending on foundation type, number of suction points required, and the routing complexity of the exhaust pipe. This is a modest cost relative to the health risk being addressed. Annual testing or a continuous radon monitor is recommended after installation to verify ongoing system performance.
Radon in Real Estate Transactions
When radon testing in a real estate transaction reveals levels at or above 4 pCi/L, mitigation is a legitimate and appropriate repair item for negotiation. Sellers can either install a mitigation system prior to closing or provide a credit for the buyer to have one installed after. Given the modest cost of mitigation relative to home values in the Portland market, buyers should not hesitate to make this a condition of the transaction.
Oregon and Washington both have disclosure requirements related to known environmental hazards. If a seller is aware of elevated radon levels from prior testing, that information must be disclosed to buyers. Buyers should also be aware that radon levels in a home can change over time as the structure settles and new pathways develop — a home that tested below the action level five years ago may be above it today.
New Construction and Radon-Resistant Features
Oregon and Washington building codes now require radon-resistant construction features in new homes in designated high-risk areas. These features typically include a gas-permeable layer beneath the slab, a vapor barrier over the slab sub-base, and a capped PVC stub-out that can be connected to a fan if testing reveals elevated levels after construction. Homes built with these features can often be upgraded to active mitigation for a few hundred dollars rather than the full cost of a new system.
Radon-resistant construction features reduce risk but do not guarantee safe levels. Testing after occupancy is still recommended for all new construction in the Portland area.
Trusted Home Inspections offers radon testing as part of our comprehensive inspection services throughout the Portland metro area and Southwest Washington, following EPA and state testing protocols. If radon testing was recommended in your report or if you have questions about testing your current home, contact us at office@trustedhome.org.