Any water that migrates from the indoors to the outdoors during cold weather can be termed vapor migration. It is the migration of water vapor through walls by a combination of vapor diffusion and air movement or leakage that carries water vapor in the air with it.
Vapor migration is occurring in all walls and is a normal mechanism for removal of moisture generated by occupants and their activities from housing.
In those instances, normal vapor migration from indoors is not a problem.
Moisture generated inside housing during cold weather in cold climates is typically removed by vapor migration and mechanical ventilation.
Therefore, the water that caused the damage had to be coming from moisture in the indoor air that was moving by vapor migration into the wall cavities.
Among the topics are the utility of continuous monitoring in detecting and predicting '"worst case" ground-gas concentrations, proton transfer reaction mass spectrometry as a real-time method for continuous soil organic vapor detection, measuring natural gas emission rates from below-ground pipelines, quality control considerations for soil gas sample collection using direct push and hand-sampling equipment, and assessing vapor migration
at chlorinated sites using induced flux measurement.
The other way moisture can damage a building is vapor migration
Air barriers prevent the passage of air, but paradoxically do not prevent vapor migration
. Air barriers are usually high-tech products made of a randomly spun plastic fiber similar to the rip-proof FedEx envelopes.
* Vapor migration
. One major and common failure of lab flooring is caused by vapor moving up through the substrate.
The excavation was filled with clean material and a bentonite layer was installed beneath the building foundation floor to create a permanent barrier to ground-water and vapor migration
into the building basement.