Tyvek as an *interior* air barrier
I’ve seen a lot of reference to membrain, intello, and other interior air barriers.
These have dynamic permeability values, but are essentially vapor barriers at low RH values, and not vapor barriers at large RH values. Membrain says to installation is ok in climates zones 4C and above, and intello I’m sure is similar.
For climate zone 3, mixed humid, or 3A, an interior air barrier has not traditionally been encouraged. However, the need for an air tight wall assembly is at the same time desired by everyone. This has lead to things like “air tight drywall” and other concepts.
I was thinking about Tyvek, and it’s use as an interior air barrier. It is more permeable than any other wall assembly component, even more so than 2″ of mineral wool. It will not stop vapor from moving through an assembly. This is a feature of the material, and it would make it unsuitable for cold climate interior vapor barriers.
I called Tyvek’s tech support line, and asked if this was a typical use. The spokesperson confirmed it can be used in this way, and provided a link to a detail showing it being installed on the interior faces of a stud wall (link below).
For warmer climates, this provides a much cheaper alternative to the smart vapor retarders, and reduces the burden for ensuring a good air seal for a wall assembly, as a backup to the exterior air barrier. There’s no sealant on drywall, slowing that process, and it can be done with materials that are often left over from other parts of build.
Question: Has anyone used tyvek this way in practice, and can you comment on how the job went? To me it seems like a no-brainier, considering the ease of installation, cost effectiveness, and greatly reduced air exfiltration(?) from the interior to the stud bays. This is more of a discussion than a question I suppose. Just wanting some thoughts.
Assume for the sake of the discussion a standard wall assembly of
(tyvek interior air barrier)
Fiberglass/mineral wool/cellulose (no sprayed foam, but vapor permeable insulation)
7/16 osb sheathing (taped seams)
2″ comfortboard / XPS
3/4″ furring strips
James Hardie / LP Smart Side siding
GBA Detail Library
A collection of one thousand construction details organized by climate and house part