When are indoor Radon levels typically at their highest?

Indoor radon levels are typically at their highest in winter, particularly in homes that are taller and have basements. This phenomenon occurs for several reasons.

First, during the winter months, homes are often sealed tightly to conserve heat, which can lead to increased levels of radon accumulation indoors since radon gas is not allowed to escape. Additionally, cold weather can increase the density of the soil, which can enhance the movement of radon gas from the ground into a home, particularly through cracks in foundations or other entry points. Homes with basements are especially susceptible because they are often in closer proximity to the ground where radon is produced as uranium in the soil breaks down.

In contrast, radon levels can be lower in warmer months when windows and doors are more frequently opened, allowing for ventilation that helps to disperse any accumulated radon gas. Therefore, the winter months, combined with the structural characteristics of taller homes with basements, align to create conditions that contribute to peak indoor radon levels during this time.