Understanding Soil Gas Entry Into Homes
Indoor moisture levels, which affect both human comfort and building durability, are influenced by moisture sources. Better understanding of moisture sources allows better indoor moisture prediction and control. One poorly characterized moisture source is the building foundation. A Forest Service research team developed a new methodology for quantifying water vapor release from building foundations. The team designed a study to measure all the flows of moisture into and out of the house, except the transfer of water vapor into the basement from the surrounding soil, which was determined by mass balance. The researchers were able to verify their model using a radon mitigation fan, which in effect could turn off both the radon and moisture sources in the soil gas. The research showed that water vapor transfer into the basement was dominated by air pressure differences, primarily the stack effect which results from the indoor to outdoor temperature difference.