Radon Re-entrainment Study—An Initial Investigation

Currently radon mitigation standards in United States residential homes and buildings require that the exhaust point for active fan-powered depressurization (ASD) systems exhaust be at or above the roofline of the building. There was very little evidence to support this requirement in the mid-1990s when the standards were published. This study was designed to examine the potential and safety of ground level exhaust. There are numerous advantages for ground level exhaust, such as aesthetics, safety, and reduced condensation, if properly placed along side of the building. A configurable exhaust point ASD design whereby we could change the exhaust from roofline to ground level was installed in 10 homes in the Harrisburg, PA, area. This design allowed us to change the configuration every 2 wk from roofline to ground level to baseline (off) conditions, with the house thereby acting as its own control, while extensively measuring the indoor and outdoor radon concentrations and other parameters over the course of 1 y. Over the year-long study, roofline and ground level exhaust configurations both showed very similar average indoor radon concentrations. Apart from the typical seasonal differences, there was little difference between average indoor radon levels for roof and ground level exhaust during each of the four seasons.