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Moisture intrusion can be the cause of building defects, as well as health ailments for the building’s occupants. Inspectors should have at least a basic understanding of how moisture may enter a building, and where problem areas commonly occur.


Some common moisture-related problems include:

  • structural wood decay; 
  • high indoor humidity and resulting condensation;
  • expansive soil, which may crack the foundation through changes in volume, or softened soil, which may lose its ability to support an overlying structure;
  • undermined foundations;
  • metal corrosion;
  • ice dams; and
  • mold growth.  Mold can only grow in the presence of high levels of moisture. People who suffer from the following conditions can be seriously (even fatally) harmed if exposed to elevated levels of airborne mold spores:
    • asthma;
    • allergies;
    • lung disease; and/or
    • compromised immune systems.

Note:  People who do not suffer from these ailments may still be harmed by elevated levels of airborne mold spores.


How does moisture get into the house?

Moisture or water vapor moves into a house in the following ways:

  • air infiltration. Air movement accounts for more than 98% of all water vapor movement in building cavities. Air naturally moves from high-pressure areas to lower ones by the easiest path possible, such as a hole or crack in the building envelope. Moisture transfer by air currents is very fast (in the range of several hundred cubic feet of air per minute). Replacement air will infiltrate through the building envelope unless unintended air paths are carefully and permanently sealed;
  • by diffusion through building material. Most building materials slow moisture diffusion, to a large degree, although they never stop it completely;
  • leaks from roof;
  • plumbing leaks; 
  • flooding, which can be caused by seepage from runoff or rising groundwater; it may be seasonal or catastrophic; and
  • human activities, including bathing, cooking, dishwashing and washing clothes. Indoor plants, too, may be a significant source of high levels of humidity.