I'm sure its a consequence of the way its made. But, it is clearly
labeled "THIS SIDE DOWN" -- as if placing it *up* would be A Bad Thing.
E.g., Plywood with different finish grades has obvious reasons why
you'd want the *good* ("A") side up -- appearance.
But, the "down" side of the OSB is the smoother of the two sides.
I can't believe there are sufficient imperfections (bumps) in
the not-smooth side that would interfere with it fitting against
[And, if so, the problem would be the same if on the *other* side!]
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.