Effect of forced convection on the hygrothermal performance of a wood frame wall with wood fibre insulation

Abstract Wood-based thermal insulation materials have interesting hygroscopic characteristics because of their high moisture capacity. The present paper investigates the moisture conditions in wood-frame walls with wood fibre thermal insulation. The effect of forced convection of moist air into the construction is studied in particular. Laboratory measurements were carried out on a full-scale wall model divided in five sections with various configurations. The wall sections had different combinations of exterior air barrier, thermal insulation and vapour retarder. Each section was prepared with an air leakage to simulate supply of moist air to the wall construction through forced convection. The measurement results provided insight in the moisture conditions in the wall and internal distribution of moisture in the wall sections. The results show that walls with wood fibre insulation may have the same risk of high moisture levels as walls with mineral wool insulation. However, the results indicate that wood fibre insulation absorbs condensation during winter periods and melting water, while the mineral wool does not. Hence, the results imply that the wood fibre insulation has the benefit of distributing the moisture over a larger volume than the mineral wool insulation. Furthermore, the investigations indicate that using an exterior air barrier with high thermal resistance results in a generally lower moisture level in the wall construction, which can be considered favourable regarding risk of mould growth.