Ecological Insulation materials are getting more and more popular, but until now their share of the insulation market is e.g. in Europe below 10 %. One of the reasons is, that architects, engineers or designers are not well informed about the advantages of their use. With the use of advanced hygrothermal building simulation tools, like WUFI-ORNL/IBP the realistic heat and moisture performance of a wall or roof assembly can be predicted easily. Unfortunately the needed material properties for the ecological insulation materials are not completed or even unknown. This work is focused on the measurement of the hygrothermal material properties. Afterwards the results are used in order to calculated the hygrothermal performance for a roof construction under real climatic conditions. With the information about the stochastical deviation of the measured data and the help of the computational sensitivity analysis, one can study how sensitive the solution of a problem based on the data confidence input and its reaction to a single parameter of uncertainty. It may also provide us the basis for simplifying some of the hygrothermal analyses by allowing us to use material properties that are representative to materials with similar but not exactly the same properties.