When is retesting recommended prior to the five-year mark?

Retesting for radon is recommended when significant changes are made to a home or building that could potentially alter the radon levels present. The correct response indicates that retesting is necessary when a new addition is built or when significant alterations are made to heating or cooling systems.

When a new addition is constructed, the structural changes can impact the airflow and radon entry points in the home. This might create new pathways for radon gas to enter or alter the mitigation effectiveness of existing systems. Similarly, significant alterations to heating or cooling systems can also affect pressures and air circulation within a building, which could either increase or decrease radon levels.

Understanding that both scenarios—construction of a new addition and substantial modifications to HVAC systems—affect radon levels helps ensure that radon measurement reflects the current state of the environment within the building. Regular retesting is essential for maintaining safe indoor air quality, as radon concentrations can fluctuate based on these changes. Hence, the need for retesting prior to the five-year mark when either situation occurs is crucial for the safety of occupants.