The prevention of moisture from penetrating a building’s interior is the job of a vapor barrier, also called a vapor retarder. Interstitial condensation is the accumulation of moisture or water vapor within a building’s cavities due to factors such as airflow, material diffusion or heat transfer; it is typically prevented by a plastic or foil sheet. Moisture vapor transmission rates are determined through standard testing and then categorized as impermeable, semi-permeable, or permeable in accordance with the standards set forth in the National Building Code (NBC).

When SPF insulation is applied at a thickness of 50mm or more, a secondary vapor barrier is not necessary. This is due to the fact that the foam creates a physical barrier against air and moisture and is an all-in-one system. However, when installing batt insulation or blown-in loosefill insulation in wall cavities, ceilings, or attics, a secondary vapor barrier is required. Our crews exclusively apply a 2mil polyamide continuous vapor barrier and smart vapor retarder, which unlike traditional polyethylene vapor retarders, block moisture in the winter when humidity in the cavity is low and increase permeability during the summer when humidity is high to let moisture escape while still maintaining air tightness. We can also apply a 6mil polyethylene vapor barrier as well at the request of the client.