Detailing ASCE 7's changes

Updated ways to determine design wind loads

Within the past few years, ASCE 7, "Minimum Design Loads for Buildings and Other Structures," published by the American Society of Civil Engineers, increasingly has been used to determine design wind loads, particularly because it is referenced in the 2000 edition of the International Building Code (IBC). Recently, ASCE 7's 2002 edition became available; it is referenced in IBC's 2003 edition. Because many jurisdictions soon may begin requiring compliance with IBC 2003, it is important you are aware of the changes in ASCE 7.

ASCE 7's new edition includes several changes and additions that apply to the calculation of roof assemblies' wind loads. Unfortunately, the changes are not delineated in the document, and it is a laborious process to determine what changes were made. I tracked the changes, and following is an overview of those pertaining to calculating roof assemblies' wind loads. (Note: Additions and changes pertaining to primary structural elements, such as beams, columns, shear walls and diaphragms that provide support and stability for the building, are not addressed in this article.)

Parapets

6.5.12.4 is a new section pertaining to parapet loads. This section directly applies to loads on parapet base flashings, which previously were not addressed in ASCE 7. When determining base flashing loads, the suction pressure on the windward parapet's roof side is determined by using the same coefficient used for the adjacent roof area.

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