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Which Side of Oriented-Strand Board (OSB) is the Top?

Q: "Which side of an OSB sheet should face up or out? "


Oriented-strand board (OSB) is inexpensive and relatively strong, and I've used it as sheathing for many years. But one question has always bothered me: Which side of an OSB sheet should face up or out? One side is smooth and the other is a little rough.
— Scott, Anchorage, AK


Tom Silva replies: It doesn't make a bit of difference from a structural standpoint. A wall, a floor, or a roof will be just as strong no matter which side faces up or out. But on a newly sheathed roof, leaving the lightly textured side up does give a bit of extra traction.
If the OSB has tongue-and-groove edges, there's another issue to consider. According to the Structural Board Association, the tongue-and-groove profile is not symmetrical, so the sheets must all be facing the same way for the joints to match. With those panels, look for the "This side down" stamp and follow that direction.


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