Moisture transport through perforated vapour retarders

Nowadays, in most cases and according to recent international standards, moisture transport in building envelopes is assumed as one-dimensional. In fact, three-dimensional moisture transport occurs due to layer perforation or building assembly details. The article is focused on cases of low-slope compact roofs with a waterproofing membrane where the vapour retarder is perforated. Water vapour permeability measurement of different vapour retarders with different degrees of perforation is done by the wet-cup method. Results are presented. A significant increase of moisture transport is found through vapour retarders although their percentage of perforation was much lower than in previous known studies. A description of setting the apparatus to measure materials with a very high water vapour resistance factor is presented. Finally, based on the results, we formulated an analytical equation that describes water vapour diffusion flux through perforated vapour retarders. A simple equation can be used in cases where only one-dimensional moisture transport is calculated, which will help building designers to determine diffusion properties of perforated vapour retarders.