Make sure that a radon test is done as soon as possible. Consider including provisions in the contract specifying:
Make sure that the test is done in the lowest level of the home suitable for occupancy. This means the lowest level that you are going to use as living space which is finished or does not require renovations prior to use. A state or local radon official or qualified radon tester can help you make some of these decisions. If you decide to finish or renovate an unfinished area of the home in the future, a radon test should be taken before starting the project, and after the project is finished. Generally, it is less expensive to install a radon-reduction system before (or during) renovations rather than afterward.
Even if built to be radon-resistant, every new home should be tested for radon after occupancy. If you have a test result of 4 pCi/L or more, a vent fan can easily be added to the passive system to make it an active system, and further reduce radon levels. Building radon-resistant features into the house during construction is easier and cheaper than fixing a radon problem from scratch later. Let your builder know that radon-resistant features are easy to install using common building materials. When installed properly and completely, radon-resistant techniques can also make your home more energy-efficient and help you save on your energy costs.
Radon Test Device Placement
Test the home with a continuous monitor for at least 48 hours.
"Closed-house conditions" mean keeping all windows closed, keeping doors closed except for normal entry and exit, and not operating fans or other machines which bring in air from outside. Fans that are part of a radon-reduction system or small exhaust fans operating for only short periods of time may run during the test.