OSB sheathing and plywood sheathing covered with a building paper or housewrap and vinyl siding are classed as vapor semi-permeable.Click to see full answer. Keeping this in view, is OSB a vapor barrier?Any material that allows less than 60NG (nanograms) of moisture to pass through under specific conditions, is considered a type 9 residential vapour barrier by the National Building Code. Rated at 40NG, 3/4 inch OSB sheathing can be one of the better vapour barriers for home construction in most of Canada.Furthermore, is plywood vapor permeable? Both 15/32-inch plywood and 7/16-inch OSB are regarded as semi-permeable materials under the 2006 IBC and IRC. For comparison, the water vapor permeance of polyethylene and some extruded polystyrene products are very low and are generally insensitive to relative humidity gradients. Hereof, is OSB board OK to get wet? Allowing OSB to get wet is not a wonderful idea but its done all the time. Most of the time there is very little harm and the material doesn’t loose strength or any of its integrity. OSB that does get wet will tend to swell and delaminate first at the edges of the boards.Does OSB board warp? Oriented Strand Board (OSB) Unlike it’s plywood counterpart, OSB lacks the forces that tend the wood to warp, and so is easier to get perfect dimensions and avoid warping tendencies. The one major disadvantage of OSB is its propensity to expand with moisture.