Hygrothermal performance of a light weight timber wall assembly with an exterior air barrier

Paper in proceeding, 2015

This paper investigates the effect of convection on moisture accumulation, and mould growth potential, in a lightweight timber frame wall system where the air barrier is situated at the exterior and the damaged or unsealed vapour retarder is situated at the interior. A two dimensional numerical HAM (Heat, Air and Moisture) model is constructed and verified to evaluate the hygrothermal behaviour of a light-weight timber frame wall system with varying airtightness attributes. The mould growth potential of the wall system in a Swedish climate is assessed and compared utilizing the data output from the numerical model simulations and a material specific mould growth index. The results suggest that the joints of the interior vapour retarder need not be sealed in the studied case. While the degree of moisture accumulation is larger behind the exterior air-tight layer of the simulated wall assembly possessing an unsealed interior OSB layer (compared to sealed interior), the influence on mould growth potential is limited.