Which of the following creates the greatest radon threat in a property?

Poor ventilation creates the greatest radon threat in a property because it allows radon gas, which is naturally produced by the decay of uranium in soil and rock, to accumulate indoors. When a home is not adequately ventilated, the radon levels can rise significantly, posing serious health risks to occupants. Proper ventilation helps to dilute indoor air pollutants, including radon, by allowing fresh air to enter and facilitating the exit of contaminated air.

While high humidity levels and old building materials may have their own implications on indoor air quality, they do not specifically contribute to the accumulation of radon gas. Concrete foundations, although often associated with radon mitigation strategies due to the potential for soil gas infiltration, do not inherently create an increased risk of radon exposure unless there is poor ventilation in the space above or within the foundation. Therefore, addressing ventilation is crucial in managing radon risks effectively.