How are you determining the rating, i.e., is this Exposure 1 or 2? I'm not disputing anything anyone is saying about OSB, but I have a lot of curiosity on how folks are figuring out ratings on material that's installed, covered, inaccessible, or destroyed. I ask, because on the Advantech that I've put out in the weather, i.e., full exposure to rain, wind, sun, snow, ice, etc., it holds up. How are you folks determining rating? This was an amateur addition to a decent old house, so I just said rip it off and put a better roof on it. Properly installed OSB roof sheathing has the stamps visible in the attic. Also in Canada, exterior grade OSB has a green painted edge you can sometimes see. It's usually OK, except if it gets wet enough for mold to start growing on it.