I’m building a high-performance home in a cold climate (Calgary, Alberta). It’ll be double-stud construction with dense pack blown in cellulose. I’d love an excuse to try out the ZIP System Sheathing products but I want to make sure they allow for enough drying potential, as in our cold winters, humid and heated indoor air flows to the exterior of the structure. 

According to a FHB article I read previously (sorry I lost the reference), above 20 perms there is no appreciable improvement in drying time but below 10 perms and you start to slow down the rate of drying. So I suppose my aim is for something between 10 and 20 perms.

The Vapour Transmission of the WRB Layer of Zip Sheathing is 12 Perms, which is about equal to that of 7/16″ OSB at 85% humidity. 

The other product I’m looking at is Pro Clima Solitex Mento 1000. It has a Perm rating of 38. Is there a benefit to going with a product that has a perm rating so much higher than the OSB it will be installed on? Or does the OSB act as a choke point and limit the drying potential of the entire structure regardless of the higher perm rating of the WRB.

Thanks for any help and thoughts.