47.5 MB - The Whole Building Design Guide

Figure 3-38:Two complete windows,including frames, blewout as a result of aninadequate number offasteners. Typhoon Paka(Guam, 1997)Where corrosion is a problem, use ofanodized aluminum or stainless steelframes and stainless steel frame anchorsand screws are recommended.The maximum test pressure used in thecurrent ASTM test standard for evaluatingresistance of window units to wind-drivenrain is well below design wind pressures.Therefore, units that demonstrate adequatewind-driven rain resistance during testingmay experience leakage during actualwind events.The successful integration of windows and curtain walls into exteriorwalls is a challenge in protecting against water infiltration.To the extent possible when detailing the interface betweenthe wall and the window or curtain wall units, designers shouldrely on sealants as the secondary line of defenseagainst water infiltration, rather thanmaking the sealant the primary protection.If a sealant joint is the first line of defense, asecond line of defense should be designed tointercept and drain water that drives past thesealant joint.When designing joints between walls and windows and curtain wallunits, consider the shape of the sealant joint (i.e., a square jointis typically preferred) and the type of sealantto be specified. The sealant joint should bedesigned to enable the sealant to bond ononly two opposing surfaces (i.e., a backer rodor bond-breaker tape should be specified).Butyl is recommended as a sealant for concealedjoints, and polyurethane for exposedjoints. During installation, cleanliness of thesealant substrate is important (particularly ifpolyurethane or silicone sealants are specified),as is the tooling of the sealant. ASTM3-54 MAKING CRITICAL FACILITIES SAFE FROM High Wind