What should be done with openings at the top course of block walls?

Sealing openings at the top course of block walls is essential to prevent the ingress of radon gas, which can be a significant health risk if it accumulates in enclosed spaces. These openings may serve as pathways for radon to enter a building, particularly in areas where radon levels are high.

By sealing these openings, you create an effective barrier to inhibit the flow of radon and reduce the overall concentration in the building's interior. Proper sealing contributes to a comprehensive radon mitigation strategy, ensuring that potential radon sources from the soil and the block walls are adequately managed.

Other options would not effectively minimize the risk associated with radon exposure. Leaving openings unsealed for ventilation could allow radon to enter, while covering with mesh may not provide a robust enough seal. Ignoring these openings during inspections undermines safety measures and places occupants at risk. A systematic approach that includes sealing these openings is crucial for effective radon mitigation.