The use of an internal airtight membrane in CLT external wall in terms of hygrothermal performance

Abstract

This study focused on the dry-out capacity of the vapor-permeable CLT (cross-laminated timber) external wall and the impact of using an internal airtight membrane. The results of the work were obtained first from the field measurements, after which the simulation model was created and validated, and the hygrothermal performance of the wall was analyzed by a stochastic approach. The results of this showed that the CLT dries out quickly and safely in a wall assembly with a high water vapor permeability, even with the large range of initial CLT MC (13-25%). When an additional airtight layer with high vapor diffusion resistance (Sd of 244 m) is added between the insulation and the CLT, the dry-out capacity of the CLT decreases significantly and there is a high probability of mold growth on the CLT surface. The risk of mold growth can be prevented when the vapor resistance (Sd) of the airtight layer is reduced to 1.5 m in a case where initial CLT MC is up to 25% and in a case where initial MC is up to 20%, the vapor resistance of an airtight layer must be reduced to 3 m.