Radon Mitigation: What It Costs and Why Testing Comes First
IllumenAir does not install radon mitigation systems. We measure. That independence is deliberate — the company telling you whether you have a radon problem should not be the company selling you the fix. This page explains how mitigation works, what it costs in our area, and where testing fits on either side of it.
What radon mitigation actually is
Radon mitigation is not air purification, and no consumer air cleaner reduces radon. The gas enters from the soil under a building, so mitigation works by intercepting it before it gets inside or by depressurizing the soil so it vents outside instead.
The dominant method in the Pacific Northwest is active sub-slab depressurization. A contractor cores a hole through the slab, excavates a small pit in the gravel beneath, and connects a sealed pipe that runs up through the building or along an exterior wall to a fan mounted above the roofline or in the attic. The fan runs continuously, holding the soil gas under slight negative pressure so radon vents above the roof rather than diffusing into living space.
Homes over crawl spaces usually get sub-membrane depressurization instead: a sealed polyethylene membrane laid over the exposed soil, with the suction point drawing from beneath it. Many older homes in Clark County and outer east Portland are built this way, and the membrane also cuts general crawl-space moisture, which matters for mold as well.
What it costs around Portland and Vancouver
Typical residential mitigation in this metro runs roughly $1,200 to $3,000, depending on foundation type, the number of suction points needed, and how far the exhaust run has to travel. A straightforward single-slab ranch sits at the low end. Multiple foundation sections, a finished basement that constrains pipe routing, or a home needing several suction points push toward the high end and occasionally past it.
Operating cost is modest but real: the fan draws power continuously, generally $5–$15 a month, plus a small heating penalty from the air it removes. Fans are typically warrantied around five years and usually last longer.
These are ranges, not quotes. Get bids from at least two mitigation contractors, and confirm they are certified through the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB).
Why you test before mitigating
The EPA action level is 4.0 pCi/L. The WHO recommends a more protective reference near 2.7, and there is no threshold below which radon is known to be harmless. But mitigation is a permanent mechanical alteration to your building, and you should not commit to one on a guess or on a neighbor’s reading.
Radon varies enormously between adjacent homes. Two houses on the same street, built the same year on the same soil, routinely differ by a factor of three or more, because what governs indoor concentration is the specific set of entry pathways and pressure dynamics in that particular building. A high reading next door tells you the area warrants testing. It does not tell you your number.
A test also establishes the baseline that determines system design. A home reading 6 pCi/L and a home reading 30 pCi/L need different suction capacity, and a contractor designing without a real measurement is guessing at the size of the problem.
Why you test again afterward
This step gets skipped, and it shouldn’t. A mitigation system is a piece of engineering that either achieves its target or does not, and the manometer on the pipe only confirms the fan is moving air — not that indoor radon actually came down.
Post-mitigation verification testing measures the result. It should be performed no sooner than 24 hours after the system is commissioned and ideally by someone other than the installer, for the same reason you would not have a contractor inspect their own work. Systems underperform for ordinary reasons: an undersized fan, a suction point in the wrong location, unsealed pathways the design missed, or a slab less permeable than assumed. All of those are fixable, and all of them are invisible without a measurement.
Retest every two years after that, and any time you finish a basement, replace the furnace or water heater, alter the building envelope, or the fan is serviced or replaced. Changes to a home’s pressure balance change its radon behavior.
Radon in a real estate transaction
Radon comes up most often during a sale, and the timelines are unforgiving. Oregon and Washington both treat radon as a disclosable condition, and an inspection contingency period rarely leaves room for a leisurely 90-day test.
If a transaction test comes back above the action level, the practical outcomes are a seller-funded mitigation with verification before closing, a price concession, or a credit at closing. Buyers who accept a credit and skip verification are the ones who discover a year later that the system never brought the level down.
How IllumenAir fits
We handle the measurement on both sides — the diagnostic test that tells you whether you have a problem and what its magnitude is, and the independent verification that tells you whether the mitigation worked. We are not compensated by mitigation contractors and we do not receive referral fees, so our number is just our number.
If a test indicates mitigation, we will tell you plainly and point you toward certified contractors in the metro. Then we will come back and verify their work.
Test first. Then decide.
Radon testing for homes across the Portland and Vancouver metro, including post-mitigation verification.