Radon Testing in Portland Transactions:
What Every Agent Needs to Know
Radon is invisible, odorless, and the second leading cause of lung cancer in the U.S. Here is how testing works, what the numbers mean, and how to guide buyers through it.
Most buyers have heard the word “radon” but have no idea what it means for their specific purchase. That is where you come in. A well-informed agent can walk a buyer through the test, the results, and the next steps without overstating the risk or dismissing it. This guide gives you the facts to do exactly that.
Radon is a naturally occurring radioactive gas. It forms when uranium in soil and rock breaks down. The gas seeps up through the ground and into homes through foundation cracks, gaps around pipes, and crawlspace openings. Once inside, it accumulates. Outdoors it disperses harmlessly. Inside, it can reach dangerous concentrations.
The Portland metro has meaningful radon presence. On the EPA’s county radon zone map, Multnomah and Washington counties are Zone 2 (moderate potential) and Clackamas is Zone 3, but elevated readings turn up across the metro and Clark County, and the EPA says every home should be tested regardless of zone. Homes with basements, crawlspaces, and slab-on-grade construction in certain soil zones all carry some risk. You cannot tell by looking at a house. Testing is the only way to know.
I am a Certified Master Inspector® with 3,000+ inspections in the Portland metro and SW Washington. Radon testing is one of the most common add-on services I perform. Here is what I have seen, and what your buyers need to understand.
Why Radon Matters in Portland-Area Homes
The EPA sets an action level of 4.0 picocuries per liter (pCi/L). That is the point where the agency recommends taking steps to reduce exposure. The average indoor radon level in the U.S. is about 1.3 pCi/L. The average outdoor level is 0.4 pCi/L. When a home tests at 6, 8, or 12 pCi/L, that is a significant difference from normal background exposure.
Oregon’s geology contributes to elevated radon in certain areas. The ice-age Missoula Floods spread sediment from uranium-bearing granites across the Portland area and the Willamette Valley. That does not mean every home is a problem. It means testing is worth doing rather than assuming.
Radon Risk Is Real and Uneven Across the Metro
- Oregon Health Authority data flag large parts of North, Northeast, and Southeast Portland as high risk for elevated radon
- Oregon City, Lake Oswego, West Linn, and Happy Valley are worth testing too; zone maps do not predict individual homes
- SW Washington, including parts of Clark County, has its own elevated zones
- Homes with basements often accumulate radon at higher concentrations than crawlspace homes
- New construction is not immune: tight, energy-efficient envelopes can trap gas that older drafty homes would vent naturally
How Radon Testing Works
I use a continuous radon monitor for a minimum 48-hour test, following EPA testing protocol for real estate transactions. I place it in the lowest livable level of the home: finished basement if there is one, otherwise the main floor. The device stays in place for 48 hours minimum under “closed-house conditions.” That means windows and doors stay closed except for normal entry and exit. No whole-house fans. No fireplaces running with open dampers. No HVAC systems drawing outside air.
After at least 48 hours, I retrieve the monitor and pull the readings. You get the full readings and a plain-English summary, with test placement noted, delivered with your inspection report.
When added to a buyer’s home inspection, the test runs $150. As a standalone service, it is $225. Both include the full readings and a plain-English summary. Full pricing is on the pricing page.
Reading the Results: What the Numbers Mean
The result is a single number in pCi/L. Here is how to think about the ranges.
Well below the EPA action level. No action required.
- Result is near or below the national average indoor level of 1.3 pCi/L; note for the record
- No mitigation recommended at this level
- Future owners may want to retest if they finish a basement or significantly change the home envelope
Below the EPA action threshold, but elevated enough that many buyers choose to mitigate.
- EPA recommends considering mitigation above 2.0 pCi/L
- A mitigation system typically brings levels to 1.0 pCi/L or below
- Installation cost is the same regardless of starting level; buyer’s call based on their preferences
At or above the EPA action level. Mitigation is recommended.
- EPA action level reached; professional mitigation is the standard recommendation
- Very high results (10+ pCi/L) should be addressed before extended occupancy
- Post-mitigation testing helps confirm the system is working; a separate test done after installation
Mitigation: What the Fix Looks Like
The most common solution for elevated radon is a sub-slab depressurization system. A licensed mitigator drills one or more holes through the slab or into the crawlspace, installs PVC pipe, and routes it to an exterior fan. The fan creates negative pressure beneath the slab, pulling radon out before it can enter the living space.
Installation usually takes half a day to a full day. The pipe exits through the side of the house or up through the roof. The fan runs continuously and is built for long-term use. Most systems are quiet and require minimal maintenance. Occasional fan replacement after many years of service is about all.
| Standard slab-on-grade (single suction point) | $800 – $1,400 |
| Crawlspace home with membrane installation | $1,200 – $2,000 |
| Complex foundation or multiple suction points needed | $1,500 – $2,500+ |
| Post-mitigation confirmation test | $100 – $200 |
Homes with existing mitigation systems still need to be tested. The system could be undersized, the fan could have failed, or foundation conditions may have changed. A system’s presence alone does not guarantee low levels.
Elevated radon is fixable. A mitigation system is a one-time installation that typically brings levels down. It is a known problem with a known solution and a typical cost range.
The Agent Workflow: When and How to Bring It Up
Most buyers do not ask about radon. That means the recommendation usually falls to you. Here is a simple approach that works.
At the offer stage: Mention radon testing when you discuss the inspection plan. It is an add-on, not a separate appointment, and costs $150 alongside the inspection. If the buyer asks why, tell them it is invisible, it is common in parts of the Portland metro, and testing is the only way to know. That is accurate and not alarmist.
When results come back low: Nothing to act on. Note the result in your transaction records. Buyers occasionally ask about retesting if they plan to finish a basement. That is reasonable.
When results come back elevated: Present the number factually. “The test came back at X pCi/L. The EPA action level is 4.0. A mitigation system typically costs $800 to $2,500 and typically brings levels down to below 1.0.” That is the information. What happens next is the buyer’s decision.
What you do not want to do is minimize the result or overstate it. The number is the number. A mitigation system is the solution. Your job is making sure the buyer understands both clearly.
For pre-listing inspections, the same logic applies. A seller who knows their radon level can address it before the home goes to market. A mitigated home with a low post-mitigation result is a clean disclosure. That is better than a high result surfacing mid-transaction.
Anywhere in the Portland metro or Clark County, radon testing is worth recommending on nearly every transaction. The cost is low. The information lasts the length of their ownership.
To add a radon test to a scheduled inspection, use the online scheduler. For questions about specific properties or foundation types, call or email directly.
Radon Testing FAQ
