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A climate sensitivity study was undertaken to analyze the effects of wind-driven rain on the performance of a stucco-clad wall using the advanced hygrothermal model, hygIRC. The performance of the wall is assessed based on whether or not the wall meets prescribed failure criteria. The failure criteria are based on the concurrent occurrence of temperature and relative humidity above thresholds of 10°C (50°F) and 95% respectively, for ninety consecutive days at any location of wood based material in the wall. The primary variables under consideration are climatic conditions, which are selected based on the moisture index (MI), and the amount of liquid water that penetrates and is deposited inside the wall. The moisture index relates to the severity of a given climate in respect to wall assemblies and is based on the degree of wetting and drying to which a wall can potentially be subjected. A number of simulations are carried out with various combinations of climatic location and internal moisture load.

From the results of simulations, it was observed that neither the total amount of rain intrusion over a year, nor a single significant wind-driven event exclusively determines the performance of the stucco-clad wall. Rather watertighness performance depends on the total balance of wetting and drying potential of a given climate. It is shown that, for specified climates, winddriven rain, frequency of rain and high relative humidity contribute to the wetting potential, whereas ambient temperature, low humidity, solar and long-wave radiation exchange with the surrounding contribute to the drying potential of the climate. It is also suggested that the wind-driven rain load might give a better indication of the severity of the climatic condition than moisture index for the wall type (stucco-clad wall) considered in this study.

Presented at Thermal Performance of Exterior Envelopes of Whole Buildings X – December 2007

Units: Dual

Citation: Thermal Performance of Exterior Envelopes of Whole Buildings X