I am putting down a laminate floor in my bedroom and have discovered a 2'x4' piece of the OSB subfloor, up against a non- load bearing outside wall, that has a dip in it. In the middle of the section, up against the wall, its 3/8" below the surrounding floor and it fans out to level at the inner edges of the piece. There is no sponginess to the floor or creaking when I walk on it and I haven't found any damage to the joists or structure below the subfloor. I assume the rim joist is just cupped beneath that section.
I can't lay the laminate over this area because it floats in midair. I wanted to use a leveling compound over the OSB to bring it up to level but the manufactures that I spoke with told me not to use the stuff unless I'm sure the OSB is exterior grade. The leveling compound will soak into non-exterior grade OSB and cause it to delaminate. None of the OSB sheets has the factory marking showing and so far I haven't been able to find a marking on the underside by pulling down insulation in the crawl space. I can't replace the OSB section because the outside wall is sitting on it.
Does anyone have a better method of leveling the OSB so I can finish laying my floor?