AbstractThis study evaluates the impact of the number of cycles of the V313 test (EN 321 2002) on the mechanical properties of 15-mm-thick OSB/3 and OSB/4. The obtained results were compared with the properties of the boards exposed to external environmental conditions. The results of the study indicate that the tested boards were characterized with a 50% decrease in static bending strength and a 70% decrease in tensile strength perpendicular to the plane. However, both types of boards met the requirements of the standard (EN 300 2006) with respect to their modulus of rupture. The method of exposing boards to outdoor conditions has a substantial influence on the change of the physico-mechanical properties of OSBs. In the boards used in this study, however, those changes occurred slower than those evoked by the V313 test, especially after an upright exposure. For these reasons, for that type of board storage, an equation was determined that can bring the property changes following the V313 test into an acceptable range to allow for the evaluation of the board properties. In the case of vertical exposure, from the second year forward, changes in the properties of the OSB/3 were similar to those presented by the boards demonstrated from the second cycle of the V313 test.