Reliability of material data measurements for hygroscopic buffering

Numerical models of heat, air and moisture (HAM) transport in building components continue to advance, but the reliability of the measured material properties, which serve as input for the HAM-models, remains very uncertain. In the framework of IEA/ECBCS Annex 41 a round robin experiment on the determination of the hygric properties of porous building materials was performed to generate a dataset for benchmarking numerical models. In the round robin experiment, 14 laboratories measured the vapour permeability and sorption isotherm of coated and uncoated gypsum board. Apart from a zero off-set due to different conditions during oven-drying, the measured sorption isotherms showed acceptable agreement. But for the vapour transmission tests, though performed according to an international standard, a wide spread in the measured data was found. The differences are most pronounced for vapour tight specimen. The large number of participants in the round robin experiment, allowed to investigate possible causes for the observed deviations. To show the importance of correct material data, the consequences of using this kind of contradictive results was investigated by calculating the impact on the moisture penetration depth and equivalent moisture capacity.