Radon levels in buildings depend on the concentration of the sub-floor soil gas and the entry points into the ground floor area. Each case must be looked at separately as these factors vary.
More radon gas can rise to the surface if the rocks and soil underneath are fragmented and porous. Possible entry points to the building for the gas include cracks or holes in the floor as well as gaps around cables and service pipes.
Generally, radon is driven by the pressure difference between the inside of the building and beneath the floor. The pressure inside is usually less.
Obviously, high levels of radon are usually found in basements and at ground level. Radon is generally of little significance in high-rise buildings.
Diagram HR1 - Example of radon main entry routes - Extract from EPA
