Yes. Test before finishing the basement, particularly if it will become a bedroom, office or family room used regularly. You cannot judge radon levels by a home’s age, appearance or your neighbour’s test result. Follow the test kit instructions and Wisconsin Department of Health Services guidance for placement and testing conditions. An early result gives you time to address elevated levels while the basement is still accessible.
If a result is elevated, follow the state’s guidance for repeat testing and discuss mitigation with a nationally certified radon professional. Share the findings when planning your basement renovation so any required system can be considered alongside the layout. Test again after major work that changes the foundation or heating and cooling systems. Finishing the space does not replace testing.