How do Moisture Barriers work?
Moisture barriers work by keeping water where it is wanted or keeping water out of areas where it is not wanted. For residential foundations resting on expansive soils (the kind of soils that move up and down and move houses), moisture barriers work by keeping excess water from flowing under foundations, where the water will cause soils to expand, resulting in a foundation moving upwards. At the same time, moisture barriers act to trap water that is already in the soils under a foundation. When water is trapped, soils can not dry out and shrink. This prevents foundations from sinking because shrinking soils cause foundations to go down.
