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Fact or Fiction: Are Radon Levels Higher In Vacant Homes?


Did You Know…?

  A home that is vacant or unoccupied will not have higher radon levels…it’s a myth! 

 How many times have you heard someone tell you this is the reason for an elevated Radon Test Result?

 We often hear that radon builds up over time if a house is vacant and closed up. This is false. The fact is that radon levels reach equilibrium (where the new radon entering the house is offset by the radon that is decaying). This equilibrium is usually reached within 12 hours of a house being closed up. (This 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. This 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…

If you opened all the windows and doors and completely aired the house out, after 24-48 hours, the original radon levels would be realized. The new radon entering the house largely equals the radon which is decaying, this again, is equilibrium.

However, radon concentration is not constant. Radon gas levels in houses vary hourly, weekly, and seasonally. These variations are mainly due to temperature differences, weather changes and house use throughout the year.

With this in mind, high radon levels cannot be a result of the house being closed up for a long period of time. Actually, closed house conditions are the ideal conditions under which to do a radon measurement – especially a short-term measurement. Short-term radon measurement is an indication of a house’s potential for radon.

Radon decay rate illustration at four-day half-life: (numbers rounded for ease of demonstration)

If day 1 radon level is 4.0 PCi, (100%), then day 64 is 1.56% concentration of the original amount (.0625 PCi). 

Day Day Day Day Day Day Day
#1 #4 #8 #12 #16 #32 #64
4.0 2.0 1.0 .50 .25 .125 .0625
100% 50% 25% 12.5% 6.25% 3.125% 1.56%

January is National Radon Month!

For additional Information:

 Do you know the Radon level in your home? No? Contact our guest author, Tiger Home & Building Inspection, to schedule a Continuous Monitor Radon Test to find out the Radon level in your home.

Tiger Home & Building Inspection /1353 Boston Post Road, Suite 8 /Madison, CT 06443 /Tel: 800-328-4677 /Fax: 203-245-2067 /Website:

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