Sub-slab depressurization systems: effectiveness and soil permeability

Sub-slab depressurization (SSD) systems in the form of radon sumps are being considered as themost effective and the cheapest radon remedial measures for existing buildings. Detailedmeasurements were made in 17 family houses that had been remediated using this system.Measurements results indicate that the performance of SSD systems depends substantially on thesoil permeability and on the presence or absence of a drainage layer beneath the floors. In case ofunpermeable soils without the drainage layer the effectiveness of SSD systems decreases, even ifthey are ventilated by continuously operating fans. On the other hand, an intermittent operation offans is usually sufficient, when SSD systems are designed for houses built on permeable soils.