Radon Test Failed at 4.8 - Would you be concerned if you were the buyer?

I recently had a home test at 14.  We thought maybe the machine was broke, so we retested.  The second test came back at 16.  THAT was concerning.  After that, I researched radon.  It is believed to be the second highest cause of cancer.  Newer homes are not built to be able to "breathe."  The cost to remediate my listing was $1,100.  I think that's a small price to pay for piece of mind.

BTW, radon tests are not common in our area either.  After that last home...I recommend one for all my buyers.

The cost of a system is reasonable, I would recommend the buyer to ask the seller to install it.  If the seller wont, follow the EPA guidelines regarding re-testing.  4.8 is not too high.  37 is my highest average--needed a system for sure.

Yes I would be concerned.  You cannot treat these issues lightly.

"Most people I've talked with feel the reading is going to be higher because the home has sat vacant for 3+ years."

A common misperception with radon is that it builds up over time if a house is vacant and closed up. The fact is that radon -- being radiactive -- reaches an equilibrium where the new radon entering the house is offset by the radon that is decaying away. This equilibrium is usually reached within 12 hours of a house being closed up. (That is why closed-house conditions must be maintained for at least 12 hours before the start of a radon test.)

Radon has a half-life of about 3.8 days. What that means is that if you had a certain amount of radon in a closed container (so no new radon could enter) and waited 3.8 days half the radon would remain. If you waited another 3.8 days half of that half (or 25% of the original amount) would remain. And so on, and so on.

Let us take a look at a house that is vacant and closed up for 28 days. How much of the original radon (the radon that was in the house when the house was closed up) remains after 4 weeks? To make the math easier let's assume the half-life of radon is 3.5 days instead of 3.8 days. After 3.5 days 50% of the original radon remains. After 7 days 25% of the original radon remains. After 1 1/2 weeks 12.5% remains. After 2 weeks 6.25% remains. After 2 1/2 weeks 3.125% remains. After 3 weeks 1.56% remains. After 3 1/2 weeks 0.78% remains. And after 4 weeks only 0.39% of the original radon remains in the house. In other words, after 4 weeks 99.61% of the original radon has decayed away. After 3 years there would be no original radon remaining in the house. It would have all decayed away. (OK, technically the remaining amount would not be zero but it would be so small that it would approach zero.)

What about the new radon that entered the house during the 4-week period? That, too, decays away at the same rate. The new radon entering the house equals the radon decaying away. This is equilibrium. (This does not mean that the radon concentration will be constant. Radon concentrations in a home are constantly fluctuatiing due primarily to weather conditions and the temperature differential between indoors and outside.)

To summarize, a high radon measurement cannot be blamed on the house being closed up for a long period of time. As a matter of fact, those are the ideal conditions under which to do a radon measurement (especially a short-term measurement).  And don't forget that a short-term radon measurement is an indication of a house's potential for radon.

Hope this helps.

We too often read about "radon buildup" being a concern in vacant homes. It's just not so. Bruce has explained this very well.

Darla--Little late on my response!  I think retesting is a good idea---if it comes in high the second time around, it needs to be mitigated!