Measuring and modelling of linear water vapour transmittance of steel sandwich panels with mineral wool

Nowadays the measurement of water vapour diffusion resistance factor of building components is performed according to EN ISO 12572 or EN 12086. Both these standards use cup methods. However, measuring vapour transmission in this way by means of linear or point water vapour bridges would be difficult because of the limited sample size and shape. Therefore in this study water vapour pressure equipment with twin chambers, according to the old Slovenian standard JUS U.J5.024 standard were used, enhanced with a guard chamber. 15 cm thick sandwich panels composed of 2 steel sheets with a mineral wool core and 5 types of joints were measured. The type of sealant used between the steel sheets (outer and inner pair) and mineral wool differs: without it, with a PUR or with an EPDM sealant. Due to the slow process of water vapour diffusion through such panels, measurements were stopped well before steady state was reached. Experimental results were modelled to obtain linear water vapour transmittance. Our modelling function contains 2 fit-parameters. Due to the vapour-guard, final results improve systematically. Modelling procedure works on panels, which are faster than standardised steady-state ones.