Approach to Assessing the Long-term Performance of Wall Assemblies – Durability of Low-rise Wood-frame walls

The long-term performance or durability of wall assemblies in respect to the moisture management of components of which comprise the wall depends on the hygrothermal response of the wall to local climate loads. Critical factors in estimating the longevity of wood frame structures include limiting the temperature range, wood moisture content and time of exposure to conditions suitable for the onset, growth and propagation of mould and rot to occur. Several approaches to assessing the vulnerability of wood frame structures to deterioration have been developed in recent years some of which suggest applying a limit-states design (LSD) approach to the performance assessment of the assembly. In this paper emphasis is placed on a further development of the LSD approach within the context of requirements set out in ISO 13823 “General principles on the design of structures for durability”. An example is presented in which the LSD approach is applied to low-rise wood-frame walls, as are built in North America, and that incorporate drainage components, such components forming part of a rain screen wall assembly. The use of this approach permits determining whether wall assemblies incorporating novel components are suitable for use in walls exposed to climates having extreme wind-driven rain conditions. The performance assessment is based on the results derived from hygrothermal simulation