From the moment it is created, radon (being a gas) evades through the pores and cracks of rocks and enters into the atmosphere, where it is quickly diffused. Radon released from soil may enter a building through numerous entries:

• tiny cracks on concrete floorings
• gaps or cracks of the walls
• gaps on wall-flooring joints
• gaps of wooden flooring
• gaps at inlet points of water supply and drainage piping
• interstices of doors and windows
• water supply

Radon concentration in the interior of a building is affected by numerous factors. The most crucial are:
• radon effusion rate from soil
• type of building foundation on the soil
• height of residence
• radon effusion from building materials of interior surfaces
• ventilation
• pressure differential between a residence interior and the external environment.