Radon is volatile. It is quite normal for radon levels to change up to a factor of 5 (5 times initial reading) within one 24-hour measurement.
Radon levels can change because of the following reasons:
- Building insulation
- Building foundation
- Use of water
In addition, no radon test is 100% accurate. Radon levels will also change because of the inherent level of uncertainty in each method of measurement.