Good Building Score: 29

Recommendation: Avoid

Water brings life, but also destroys many things. Therefore, one of the most important rules in building science is that drying potential must be greater than wetting. It’s impossible to fully prevent things from getting wet so it’s necessary to build significant drying reserves into our building enclosure systems.

Zip Sheathing is made using Oriented Strand Board (OSB) sheathing. It isn’t our favorite material because the glues can be toxic, but more importantly, the mix of glue and wood chips doesn’t end up creating much drying potential. Even when OSB gets wet it has a hard time drying because of low vapor permeability.

The Weather Resistive Barrier (WRB) membrane adhered to the OSB is vapor permeable; however, since it’s directly adhered to the OSB we need to think of the product as one complete system. Since the OSB isn’t very permeable, it means the whole system isn’t very permeable. Further exacerbating this issue is that the Zip tape used on seams between panels is also vapor closed. The seams could be an opportunity to create some minor dying potential, but this is typically blocked off with Zip tape.

In summary, Zip sheathing, and Zip system as a whole, creates a relatively airtight system with far lower drying potential than would be ideal. This might be ok or it might cause rapid rot/mold failures depending on climate and installation.