Notes: Guidelines have been given at national level but also by several Italian Regions in the framework of the National Radon Action Plan 2002-2020. The new legislation on radioprotection (Legislative Decree 101/2020) requires that the new National Radon Action Plan (under preparation) have to include specific regulations to prevent the ingress of radon in new buildings as well as in existing ones (in the latter case only for major renovations, remodeling and alterations). All the 21 Italian Regions will have to include such regulations in their building codes.  