Radon, insecticides, methane, water vapor and other gasses from the soil can enter through pores of basement floors and walls made of concrete.
1. Moisture Control Handbook: Principles and Practices for Residential and Small Commercial Buildings, by Joseph Lstiburek and John Carmody. A manual for understanding moisture problems and control methods of all types.
On page 41, the authors discuss entry of water vapor and radon from the soil through the pores in concrete basement floors and walls when indoor air pressure is less than the pressure of gasses in the soil.
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2. Understanding Ventilation: How to Design, Select, and Install Residential Ventilation Systems, by John Bower.
Page 118: "A number of pollutants are present in the soil around houses that are not good to breathe: radon, pesticides, herbicides, sewer gas, etc. They often get sucked into the living space through random cracks, holes and gaps in the foundation when a house becomes depressurized. Excessive amounts of moisture can also be pulled from the soil into the living space."
Page 122: "Moisture entering a house from the ground is one of the most significant ways water vapor gets into houses. In fact, it often dwarfs the amount of moisture generated indoors by the occupants." NOTE: About 6 pounds of water vapor per person is released into homes each day by cooking, breathing, washing clothes, bathing, etc.
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3. Pore Structure and Permeability of Cementitious Materials: Symposium Held November 28-30, 1988, Boston, Massachusetts, U.S.A. (Materials Research Society)
This book discusses the reasons why ordinary concrete is so porous that an air pressure differential can force water vapor, and other vapors, from the soil into buildings.
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