Accuracy of water vapor permeability of building materials reassessed by measuring cup's inner relative humidity

Cup experiments are the most widely used method to measure water vapor permeability of porous building materials. For this test, cup assembly is designed create a pressure gradient across sample and, thus, allow diffusion through it. Water assessed by weighing over time. While external conditions generally well controlled, appropriate solid desiccants or saturated salt solutions control inside cup. However, precise knowledge these crucial, as they calculate permeance and hence permeability. In study, dry wet were performed with different on nine materials Sd-values ranging from 0.08 m more than 1 m. all experiments, relative humidity within air layer in was measured wireless sensors. The results showed that rarely same expected value desiccant also varied time, resulting 5% 450% errors predicted Sd-value. A correction proposed assess “real” Sd-value theoretical differences between discussed.