Radon Testing and What a Result Actually Means

A buyer has asked for a radon test and your first instinct is that Oklahoma is not a radon state. That instinct is half right and it is the half that gets people into trouble, because the map everybody quotes says in its own text that it must not be used to decide whether a particular house is tested.

This article covers what radon is, what the zone map does and does not tell you, what the numbers mean, how testing works around a sale, and what mitigation involves.

What it is, briefly

Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It enters buildings from the ground, through cracks in slabs, foundation joints, sump openings and crawl spaces.

It cannot be seen, smelled or tasted. There is no symptom that tells you a house has it, and no inspection that reveals it visually. Testing is the only way anybody knows.

It is measured in picocuries per litre, written pCi/L, and that unit is all the arithmetic you need.

The zone map, and what it actually says

Almost every conversation about radon in Oklahoma runs into the EPA's Map of Radon Zones, and almost every one of them misuses it.

The map was developed in 1993 to help governments and organisations target risk reduction activities and resources, using indoor radon measurements, geology, aerial radioactivity, soil parameters and foundation types. Counties are placed in one of three zones by predicted average indoor screening level: Zone 1 above 4 pCi/L, Zone 2 between 2 and 4, Zone 3 below 2.

EPA's own words on the document: the Map of Radon Zones should not be used to determine if individual homes need to be tested. Homes with elevated levels have been found in all three zones.

So a low zone is a statement about a county average from a thirty-year-old predictive model. It is not a statement about your house. EPA also points readers to a USGS report on variation within counties, which is the whole problem with reasoning from a county colour.

What the map says about this area

Published readings of the map put Tulsa County, and the neighbouring Osage, Rogers, Wagoner, Creek, Okmulgee and Washington counties, in Zone 3, the lowest band. Mayes and Cherokee counties, among others to the east, are reported as Zone 2.

That distinction matters on this site because it runs through our own service area. A house in Tulsa or Sapulpa sits in the low band; a house in Pryor or Tahlequah sits in the moderate one. Our page on which county handles your town covers the county boundaries, which do not follow town names.

One source reading CDC testing data puts the Tulsa County mean at around 1.8 pCi/L across a few hundred tests. We are attributing that rather than asserting it, because it is a secondary reading rather than an EPA figure.

None of which tells you about your house. That is not a rhetorical flourish; it is what the map itself says.

The numbers that matter

Two thresholds, both from EPA:

Fix your home if the level is 4 pCi/L or higher.

Consider fixing if the level is between 2 and 4 pCi/L.

Those are the only two numbers in this article that decide anything. A result of 1.2 is a non-event. A result of 3.1 is a conversation. A result of 6 is a job.

Testing around a sale

Radon testing is not part of a general home inspection. Our article on what a home inspector checks lists it among the specialist tests that appear in a report as a limitation rather than a finding.

Practical points if it comes up in your transaction:

• Short-term tests are what transactions use, because they produce a result in days rather than months. Long-term testing gives a better picture of the actual annual average, which is what matters for health, but nobody delays a closing for it
• Closed-house conditions matter. A short-term test is run with the house closed up, and airing the property during it invalidates the result. Do not "help" by opening windows
• Do not run your own kit and hand the result to a buyer. For a transaction, use somebody independent, for the same reason we say it about mold, meth and water testing throughout this site
• Results vary between buildings on the same street, so a neighbour's test tells you nothing about yours
• The Oklahoma Department of Environmental Quality runs a radon programme and has offered free test kits. That is worth checking with DEQ, though for a transaction a professional test is the one with documentation attached

If a result comes back high

The reassuring part of this subject is that mitigation is well understood, standardised and not especially expensive relative to most things a buyer's inspector raises.

The usual method is sub-slab depressurisation: a pipe drawing air from beneath the foundation, a fan, and a vent discharging above the roofline. On a crawl space property the approach differs, and our article on crawl space against slab covers why the construction changes the answer.

We are not publishing a cost figure, because it depends on the foundation, the layout and the access. Get three written quotes from contractors who have been at the property, ask each what standard they work to, and ask specifically whether a post-mitigation test is included.

The post-mitigation test is the part that matters to a sale. A system installed with no follow-up test proves nothing. A system with a test showing the level came down is a documented, closed item.

What to tell a buyer

A test result you have, a mitigation system installed, and any known previous elevated reading all belong on the disclosure form. Our article on Oklahoma seller disclosure requirements covers the position.

The thing not to do is what people do with several subjects on this site: dismiss it because of the zone. Saying Oklahoma does not have radon, to a buyer holding a test result that says otherwise, damages the transaction more than the number does.

Where we come in

Radon is rarely a reason to sell differently, and we should say so plainly. Testing is cheap, most results in this area come back low, and where one does not, mitigation is a defined job with a documented outcome. A house with a system and a follow-up test sells to ordinary buyers at an ordinary price.

Where a cash sale becomes relevant is the usual place: when the radon result arrives alongside a longer list, when a buyer has already withdrawn and you are out of time, or when the property needs work you are not going to fund. Our page on selling a house that needs repairs sets out how the number is built.

If a test is all that stands between you and a normal sale, run the test.

The short version

• Radon is a naturally occurring radioactive gas from soil and rock. It cannot be seen or smelled and testing is the only way to know
• The EPA zone map was built in 1993 to target resources, and says in its own text that it should not be used to decide whether an individual home is tested
• Homes with elevated levels have been found in all three zones
• Published readings put Tulsa County and most neighbours in Zone 3, with Mayes and Cherokee in Zone 2
• Fix at 4 pCi/L or higher. Consider fixing between 2 and 4
• Transactions use short-term tests under closed-house conditions. Do not open windows during one
• Use somebody independent rather than your own kit
• The post-mitigation test is what makes a system worth anything in a sale