Basements have elevated radon more often than slab on grade which have elevated radon more often than crawl space homes.

Back in 1987 Alabama participated in the EPA national radon survey. 789 of our participants were self select, meaning they responded to our request for volunteers. 1,299 of our participants were randomly selected for solicitation by the EPA contractor. In areas of Alabama with significant indoor radon, the occurrence of homes with radon test results greater than 4 pCi/l was about twice as great in the self select participants as in the random select participants! Twice as great a % over 4 pCi/l.

In that 1987 study participants responded to a 35 question questionnaire about how their home was constructed and weatherized. Because we had no money for radon, we used a DOE weatherization grant to fund the questionnaire on weatherization and that provided our match for the EPA State Radon Survey which provided the canisters. I am told that such wouldn't be allowed today as the rules have since changed so you can't count federal dollars from other sources to match any federal grant.

The only statically valid conclusion from the questionnaires of 2,088 respondents who completed both the questionnaire and the radon test was that Alabama homes with basements have elevated radon more often than Alabama homes built slab on grade and Alabama homes built slab on grade have elevated radon more often than Alabama homes built with crawl spaces. The study showed no correlation between storm doors and/or storm windows and elevated radon. After we analyzed the data, students at both Auburn University and Tuskeegee University also analyzed it. They came to the same conclusions. The DOE weatherization people were very happy with the results.

But why did the self select participants had elevated radon twice as often and the random select participants?

Because it turned out that in the high radon areas of Alabama the self select participants had basements in about twice the rate as the random select participants!

Apparently in 1987 the population had heard or otherwise gotten the idea that basements were associated with elevated radon (from the TVA phosphate slag block scare) and thus people with basements were more apt to volunteer for our 1987 radon study.

I saw where there was to be a paper on building footprint and radon in St Louis. I wonder if they will have similar conclusions.