Radon comes primarily from the soil under a building. Radon can be found almost everywhere because radium (the “parent” of radon gas) is present in most soils. Average concentrations of radon are usually low, and small amounts of radon are measurable in the air. However, when homes, schools and buildings are erected over a source of radon, the gas can become trapped and elevated inside the building. The highest levels are usually detected in the basement, however heating and air conditioning systems and whole house vacuum systems can quickly spread radon to other parts of a building.