We often think of the foundation of a building as being absolutely solid. While this is the ultimate goal, it is not often true. Buildings can sometimes be faced with a phenomenon known as vapor intrusion. Contaminated groundwater or soil can emit dangerous gasses that find their way up and into structures.
An important factor to consider when building in Los Angeles is the presence of the natural gas methane in the soil.
Passive vapor barrier mitigation systems generally involve two main components: the sub-slab ventilation system, and the actual membrane engineered to block vapors from passing through.
Anyone who has lived in southern California long enough knows that this is fault country, and if you are a property owner you have an obligation to yourself to safeguard your property against damage from earthquakes. Earthquake prediction science is as yet not developed enough to know when one will strike.