Division 7 Ebook Page 539 FOAMULARŪ XPS Insulation Resisting Water Absorption (Comparing Types of Rigid Foam Plastic Insulation)

Technical Bulletin FOAMULAR Extruded Polystrene Insulation Resisting Water Absorption, the Key for High Performance Foam Plastic Rigid Insulation the board may control perm rating regardless of board thickness. For example, unfaced FOAMULAR XPS 250, 1" thick, has a rating of 1.1 perm. 2" thick has a rating of 0.70 perm, or, about equal to that of 15/32" oriented strand board sheathing (OSB). Faced FOAMULAR XPS sheathing, such as IS and PRO Pink , 1" thick, have lower ratings of 0.20 perm. A common interior vapor retarding material such as 6 mil poly has a rating of 0.06 perm. Using the perm comparison alone, FOAMULAR XPS (higher perm rating) lets water vapor out, much faster than 6 mil poly (lowest perm rating), lets water vapor in. With that imbalance of inside (lower) versus outside (higher) perm ratings, the possibility of trapped moisture, or a "double vapor barrier, is reduced. The Effect of Foam Plastic Insulating Sheathing on Dew Point More importantly, when FOAMULAR insulating sheathing is used, because it is insulation, it keeps the materials and surfaces inside the wall warmer, thus lowering the occurrence of "dew point" within the wall. Warmer surfaces are more tolerant of water vapor because, at any given vapor concentration, a warmer surface condenses less vapor than a colder surface. Figures 8 and 9 show dew point occurrence on the inside face of OSB sheathing for walls with R3 and R10 foam plastic sheathing respectively, across all U.S. climate zones from south (i.e., southern Florida, Zone 1), to north (i.e., northern Minnesota, Zone 8). The Figures compare each sheathing condition to the same wall with no "continuous insulation" (ci) sheathing. Figure 9 R-10 Sheathing, Influence on Dew Point Occurrence 9 1 2 3 4 5 6 7 8 0% 10% 20% 30% 40% 50% 60% 70% 80% R10 no ci % of Time at Dew Point Climate Zone Seattle Baltimore Inside Face of OSB in year 2 & 3 open symbols with interior VB Figure 8 R-3 Sheathing, Influence on Dew Point Occurrence 9 1 2 3 4 5 6 7 8 0% 10% 20% 30% 40% 50% 60% 70% 80% R3 no ci % of Time at Dew Point Climate Zone Seattle Baltimore Inside Face of OSB in year 2 & 3 open symbols with interior VB

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