Thomas E. Thies
I am a retired radon mitigator in New Mexico. I have been using soil gas mat without gravel in NM for 15+ years. This SGM system is installed without gravel on well compacted soils. I have never had a post installation test fail. This system has been used on single family houses and multi family 3 story residential structures up to 20,000 SF foundation footprints. Gravel is not used in 90+% of our foundations because of the high structural quality of our soils. The few contractors that have tried the gravel base are not converts and believers in a properly designed/installed SGM system