Passive radon mitigation systems are a recently required option for new construction. They are similar to active systems, but do not include a fan. They operate under the assumption that the radon will naturally vent upwards through the piping, since it is easier that pushing through the concrete floor. If passive radon mitigation does not reduce the radon to the desired levels, a fan can be added to the system later.
Due to Illinois state law, passive radon mitigation systems are only installed during new construction, because it is difficult to test radon before the building is built. Research shows that these systems can reduce radon levels, but about 70% of them still need a fan added to cope with high radon. Adding a fan later is called “activating a system”.