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EIFS manufacturers have made significant strides in successfully remedying the entrapped moisture problem by adding a drainage plane. Figure 4 Voids created through vertical adhesive patterns and/or strips of manufactured drainage material maintain effective drainage, without overly decreasing R-value. Figure 5 Many are specifying rigid board stock insulation to be applied outside the wall sheathing, but this may create a system remarkably similar to early EIFS—and without the benefit of the drainage plane. EIFS and entrapped moisture There are additional scenarios that have caused a great deal of problems. For example, issues occur when board stock rigid insulation is layered against other rigid insulation or exterior sheathing, or when decking traps moisture between the layers of material. This phenomenon first happened on a wide scale in early exterior insulation and finish systems (EIFS). Moisture entered these systems and became entrapped behind the rigid insulation and in front of the wall sheathing on the backup wall, deteriorating the water-resistant barrier (WRB), sheathing, and structural studs (Figure 3, page 70). Moisture entering these early EIFS assemblies (through any of the methods previously mentioned became held for an extended period in the pockets/ voids in the exterior building envelope created by the variations between the rigid insulation surface and the wall sheathing surface. This negative scenario was amplified by the composition of the two layers of materials involved. The EIFS industry started addressing this problem by incorporating a 3.175-mm ( 1 / 8 -in.) drainage plane between the back side of the board stock rigid insulation and the exterior face of the sheathing or the WRB installed over the sheathing. Created through vertical adhesive patterns and/or strips of manufactured drainage material (Figure 4), this void became the accepted solution because it caused the least decrease in R-value while maintaining effective drainage characteristics. It also allowed accumulating moisture to effectively drain down and out the wall. Additionally, this size was chosen because anything smaller could have allowed capillary action. When a wet layer is in close proximity to a dry one (i.e. less than 3.2 mm [ 1 / 8 in.] of separation), moisture moves between them. As the Whole Building Design Guide states: Once wetted, capillary transfer within, or between, layers of an exterior wall assembly can also occur, and can be further exacerbated by moisture loads inherent to an exterior wall product or material shortly after initial installation. 2 These voids are not widely promoted features of EIFS because the cladding systems qualify, 72 the construction specifier | september 2013 CS_September2013.indd 72 8/14/13 8:59:26 AM Lafarge