Application of Hygrothermal Analyses to Optimize

The design of exterior walls in a building envelope for optimum moisture management is a challenging task. Many conventional methods or local practice guidelines are available for this purpose, based primarily on regional traditions and with limited performance assessment records. In recent years, new wall systems and unconventional materials have been introduced in every part of North America for reasons such as aesthetic appeal, cost-effectiveness etc. However, neither the long-term moisture management performance of these new wall systems nor the uses of unconventional materials have been assessed rigorously. The primary reason for this lack of such assessment is the absence of a design-oriented technical routine to perform the task. Recent studies at the Institute for Research in Construction (IRC) / National Research Council (NRC) of Canada, show that such an assessment is possible with the use of an advanced hygrothermal modelling tool, such as hygIRC, developed in-house at IRC. This paper presents results from hygrothermal modelling and discussion on walls with the four different cladding systems: stucco, exterior insulated finish systems (EIFS), masonry and siding. These walls were virtually exposed to several North American climates. Their hygrothermal responses were assessed with a novel indicator, called the RHT index, which is derived from relative humidity and temperature. The results and discussion presented in this paper clearly show the need and usefulness of an integrated design methodology for the moisture management of exterior wall systems that can help to optimise various design considerations