What Ohio's radon maps can and cannot tell you

The EPA divides the country into three radon zones. They were built from indoor measurements, geology, aerial radioactivity, soil parameters and foundation types, and they are colour-coded on a map published for every state including Ohio.

The EPA is explicit about what the map is for: to “assist national, state and local organizations to target their resources and to implement radon-resistant building codes”. It is a planning instrument for agencies and code officials. It was never built to be a lookup tool for homeowners.

This is worth quoting rather than paraphrasing. On its own page describing the map, the EPA writes: “The Map of Radon Zones should not be used to determine if individual homes need to be tested. No matter where you live, test your home for radon.”

The Ohio map itself carries the same warning in its own margin, and adds the part people miss: “Homes with elevated levels of radon have been found in all three zones. All homes should be tested, regardless of zone designation.”

That is the whole point. A zone is a prediction averaged across an entire county. Your house is one building, with one foundation, one set of openings and one way of moving air. Two houses on the same street routinely return different readings, which is exactly why a county-level average cannot stand in for a measurement.

Ohio publishes radon measurement data by county and zip code, and several private sites republish it in more convenient form. It is real data and it is worth looking at. What it is not is a survey of the housing stock.

Radon datasets are built from tests that somebody chose to run and chose to report. Houses get tested for reasons: a sale is pending, a basement is being finished, a neighbour came back high. That is not a random sample of the homes in an area, and an average built from it does not describe the house next door, let alone yours.

Use the maps the way the EPA intends them. They tell you that this region warrants attention. They do not tell you what is in your basement.

Results come back in picocuries per litre, written pCi/L. The EPA has set the action level at 4.0 pCi/L; the Ohio Department of Health puts it plainly, saying that at that level or higher it is highly recommended to install a mitigation system.

Below it there is still a judgment to make. ODH is direct on this point too: any radon level poses some health risk, it is not possible to reduce radon to zero, and the best approach is to lower the level as much as reasonably possible. Between 2.0 and 4.0 the decision usually turns on how the lower level is used, because a storage basement and a bedroom are different exposures at the same reading.

On why any of it matters, ODH states that radon is the number one cause of lung cancer for non-smokers and the second leading cause among smokers, and that an estimated 21,000 people die each year in the United States from radon-related lung cancer.

The Ohio Department of Health runs a federally funded radon programme in cooperation with the US EPA and local health departments, and free radon test kits are available to Ohio homeowners through it. Registration is at ohio.radon.com, and the programme's education staff can be reached on 614-728-0272.

We would rather you knew that than not. A free kit is a perfectly good way to find out whether you have a problem at all, and if the reading comes back low you have spent nothing and can retest in a couple of years.

Radon work is licensed in Ohio. The Department of Health licenses the contractors who install mitigation systems, the specialists who design and supervise them, radon testers, radon laboratories and the companies providing the required training.

That means the question “are you licensed in Ohio?” has a checkable answer, and it is a fair one to ask of anybody quoting on your house, ourselves included. The programme's licensing staff are on 614-752-4425.

Test the house. It is the only step that produces a number about your building rather than your county, and both the EPA and ODH say so in almost identical words: a test is the only way to know how much radon is in your home.

If the result is low, nothing further is needed and you retest in a couple of years. If it is high, the design of any system should follow measurements taken inside your house, not the zone your county sits in.