Which way should my OSB roof board’s be installed?
OSB roof panels should always be installed with the grade stamp facing into the attic and the screened surface (with the nail guide lines) facing up. When the grade stamp is covered by roofing, the building inspector will not be able to confirm that the correct OSB roofing panel was used. The screened surface also provides a little more traction for construction workers during installation. The same goes for wall sheathing and flooring panels; always install with the grade stamp up so that inspectors can do their jobs easily.
Having said that, it is very important that the sheathing be installed with the strength axis perpendicular to the trusses/rafters. The strength axis is usually the long direction of the panel but the grade stamp will indicate it. Be very careful on hip roofs along the hip to make sure the strength axis does not mistakenly get parallel to the supports as that may result in the panel exceeding the maximum span allowed for that thickness. Sagging may result if panels are installed incorrectly.