Hi Bob,
There is no true national building code, just a patchwork of adoptions, mostly of the IRC Appendix F. See this page on the AARST website for an overview. I would be glad to help you with more background. If you'd like, let's set up a call.
Jane Malone
nationalpolicyataarstdotorg

Hi Lynda,
Possession of a credential from NRPP is not a prerequisite for joining AARST.
Jane

Radon testing, followed by mitigation if needed, is mandatory in assessments for multifamily loan transactions backed by US Department of Housing and Urban Development / Federal Housing Administration, as well as Fannie Mae and Freddie Mac, which are Government-Sponsored Enterprises in public receivership under the Federal Housing Finance Agency. These three entities’ lending pretty much covers the US multifamily lending market.
HUD’s policy is the most comprehensive; the latest draft, to take effect this fall, is posted at https://www.hud.gov/sites/dfiles/Housing/documents/2020mapguifefrafttitlepgtocs.pdf Similar radon policy is in effect for HUD loans for residential care facilities.