For Lenders: Important Radon Mitigation Considerations Maximizing Lender Security, Minimizing Risk SSD is Simple, Effective and Reliable System EffectivenessSubSlab Depressurization SSD is highly effective where subslab conditions include airspace, highly permeable soils and crushed rock or gravel.SSD can be much less effective where the soil directly beneath the slab is densely packed, a code requirement in Florida and elsewhere. System Reliability