Wood and organic materials
Which is better, OSB or Plywood for Roofs, Walls & Floors?
...WRB) you install next, and those range from about 5 or 6 perms to up around 60 perms.
Here is an example of that, assuming the 2 perm rating:
2 perm 7/16 OSB sheathing with a 30 perm WRB results in 1.88 perms
2 perm 7/16 OSB sheathing with a 5 perm WRB results in 1.43 perms
That may not seem like a lot, but...