Another source of human exposure in home and building settings is the tendency for radon gas to enter structures via diffusion through their foundations and from certain
construction materials.
Radon gas availability in structures is mainly associated with the concentration of radon in the rock fractures and soil pores surrounding the structure and the permeability of the ground to gases.
Slight pressure differentials between structure and soil foundations, which can be caused by barometric changes, winds, and temperature differentials, creates a gradient
for radon gas to move from soil gas, through the foundations, and into the structural atmosphere.