Fiberlite Technologies does not recommend the use of an interior vapor barrier with our wall cavity spray products. A vapor barrier will greatly inhibit the air movement within the cavity space which in turn regulates the temperature within the cavity.
Convective air cycles occur when an insulation product does not restrict air movement within or around the wall cavity, which allows for greater temperature variations that lead to moisture formation on wall surfaces. When insulation is improperly installed, such as gaps between the insulation and wall surface, this will promote the convective air cycle and will greatly increase the conditions for moisture to form on wall surfaces.
When cellulose insulation is spray applied into the wall cavities, a monolithic bond with the frame is formed and prevents the convective air cycle within the cavity. Thus the need for a vapor barrier is eliminated.
If you have a building official who insists that you use a vapor barrier with our products, feel free to have them contact us.