Stochastic building envelope modeling—the influence of material properties

In building envelope systems, the transport and storage of moisture impacts the basic porous structure layout. In many materials, dimensional changes occur when moisture levels are high enough. Most building materials and their respective material properties also change as a function of time. To complicate matters further, materials from one production batch to another may have substantially different hygrothermal, mechanical, and chemical properties. Even when two exact building material specimens are manufactured, their installation in the same wall design by two different craft persons may not be the same. Workmanship differences vary not only nationally but also locally from person to person. Material properties and workmanship issues must be appropriately addressed in the hygrothermal design of building constructions. These effects can only be taken into account by the use of advanced stochastic hygrothermal models in order to predict the hygrothermal performances of building envelope systems for a wide range of potential conditions. In this paper, two hygrothermal models (WUFI-StOpStar and LATENITE VTT) are used and compared with both deterministic and stochastic solutions. A MONTE CARLO stochastic model (MC) was incorporated into each hygrothermal model, and the models were employed to investigate the effect of nonhomogeneous differences in material properties for a stucco clad wall system. In the first series of simulations, the variations implemented in the model were obtained by performing an extensive amount of laboratory measurements. In the second series of simulations, a parametric investigation was performed to examine the particular influence of the exterior sheathing board on the performance of the same stucco clad wall system. The use of stochastic modeling in the area of hygrothermal analysis is novel and provides better understanding of the performance of “real envelope systems.” This is of particular use for building envelope performance assessment to determine what elements of the design are critical.