Hygrothermal Performance of a Hygroscopic and Permeable Wall Assembly: Impact of a Vented Wall Cavity

Building envelopes that are hygroscopic and permeable to water vapour can contribute to improve the Indoor Environmental Quality (IEQ) in buildings by reducing indoor humidity fluctuations and the concentration of some contaminants like CO2. However, risks of interstitial condensation and mold growth need to be assessed to ensure the durability of such building envelopes. The objective of this paper is to perform hygrothermal simulations of a case study house designed with a Hygroscopic and Permeable Building Envelope (HPBE) and to assess the impact of having a vented cavity compared to a face-sealed wall.
This contribution presents hygrothermal simulations of a wall assembly performed with WUFI Plus and WUFI Pro. The mold index is calculated from the simulation results and the hygrothermal performance of the vented and unvented wall is compared. The resilience of the construction is assessed by introducing leaks within the envelope. Simulation results indicate a satisfactory performance of this wall assembly regardless of the presence of a vented wall cavity. The wall design with a vented cavity seems more resilient when subjected to large leakages, although the wood fibreboard surface seems more vulnerable to mold growth when unprotected by a plaster. Additional simulations and field data are needed for assessing the benefits of having a vented cavity for HPBE.