Wind/Water/Codes Coverage – Myths and Realities

There are many issues related to the building envelope and fenestration elements, and Daniel Lavrich, PE, provided Southeast Region Winter Meeting participants with a survey of the “Myths and Reality” associated with each.With regard to design, Lavrich underlined the importance of designing to code-mandated regional wind velocities and testing for...
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There are many issues related to the building envelope and fenestration elements, and Daniel Lavrich, PE, provided Southeast Region Winter Meeting participants with a survey of the “Myths and Reality” associated with each.

With regard to design, Lavrich underlined the importance of designing to code-mandated regional wind velocities and testing for structural performance, water penetration (typically more pronounced on the windward side of buildings) and impact resistance per NAFS.

Breach of the envelope and resulting interior damage due to water penetration is typically the focus of hurricane damage, which in turn requires impact protection for the entire building envelope, not just glazed areas. Protection of the occupants and contents should be the primary concern. Lavrich called for more attention to the design of the building envelope to resist water penetration.

Looking more closely at fenestration assemblies, he noted that special care must be devoted to preventing failure of fasteners, wood bucks and/or the substrate and ensuring that all weatherseals are properly installed. Furthermore, maintenance is essential to counteract the effects of worn weatherseals, corroded fasteners and deteriorated hardware.

Lavrich, whose career has been devoted in large measure to understanding the actual causes of structural failure imposed by hurricanes, noted that, when analyzing the failure of a fenestration assembly, it is important to determine if the assembly actually failed or if damage was due to attachment or configuration of the substrate that did not meet code. Jumping to conclusions or using vague broad-brush terms such as “compromise” of the structural capacity of the assembly or “fatigue” of structural elements to describe failure modes, does little to help analyze actual failures or help manufacturers improve designs.

Inspections of several thousand fenestrations in numerous high-rise buildings from four to 55 years old disclosed that the key issue was water intrusion, not structural damage, which was almost non-existent in every case with only a few minor exceptions. "This surprised me," he said.

Lavrich concluded that there are “several serious defects in the production and delivery of an effective water resistant exterior envelope,” particularly with regard to fenestration assemblies likely to be subjected to high wind events. These defects highlighted the need to pay more attention to water resistance where fenestrations are incorporated into the envelope.

Manufacturers should be aware that when water penetration occurs, there can be both design and construction/installation issues. These include paying more attention to water resistance where fenestrations are incorporated into the envelope. Better definition and monitoring of installation procedures and greater emphasis on maintenance are recommended. Stronger codes and standards, better envelope design, and better installation and maintenance are the keys.

Source: aamanet.org