As any other wood product, OSB exhibits mild dimensional changes (shrinkage or dilatation in length/width) when exposed to changes in moisture and temperature of the surrounding environment. This effect is covered in the design of the structure by using sufficient expansion gaps.
In order to limit the dimensional change effects, different technical classes (types of boards) are available. This is to ensure that the right board is used for the different conditions of various applications (external wall, roof etc).
As a general rule, OSB must always be protected from direct contact with water (rain, snow, infiltration) during all stages of its intended use – from warehouse to job-site storage, transportation, installation and daily use within the building lifetime.