Nowadays to predict hygrothermal performance the methodology of ISO 13788:2012 is widely used. In calculations according to this methodology no material properties are taken into account that leads to overestimate of the risk of interstitial condensation. Therefore in order to provide insight how much results determined according to ISO 13788:2012 can differ from the actual hygrothermal performance the ribbed plywood plate with different opposite surface temperatures was tested. Temperature and relative humidity of the surfaces and internal layers were measured. After data comparison obtained experimentally and by calculation according to ISO 13788:2012 it can be seen that condensation in contrast to the predictions does not occur. Therefore on the basis of this methodology it can be wrongly concluded that analyzed envelope is unsuitable for exploitation. Hence new more accurate calculation methodology is necessary for prediction of hygrothermal performance.