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.
What is Sub-slab Ventilation System?
The sub-slab ventilation system generally consists of special flexible perforated pipe and gravel in a network of trenches. In certain jurisdictions, a special flat ventilation pipe may be used in lieu of trenching, but its use is limited to jurisdictions where this is allowed.
Currently, the city of Los Angeles does not allow flat ventilation pipes and requires conventional sub-slab ventilation system.
What is a Membrane System?
The other main component of a vapor barrier mitigation system is the membrane. Membranes are manufactured by various corporations and are rated or approved for various uses. For example, a barrier that has been approved for methane gas may not necessarily be approved for use against other vapors, such as PCE.
Both the sub-slab ventilation system and methane membrane are advanced underneath and before the concrete slab of the building is poured.