Radon systems for stone foundations are a bit tricky because stone walls and floors have lots of gaps where radon can seep in. A typical setup uses a sub-slab depressurization system, but you have to seal all those cracks and joints really well first. It's not as straightforward as with poured concrete, but a good contractor can make it work by creating a continuous suction field under the slab and ventilating it outside. radon systems for stone foundations 8