FM Global's 2006 revisions to its wind-related guidelines have
renewed interest and caused considerable discussion within the U.S.
roofing industry regarding proper wind-resistant design for
low-slope roof systems. For more than 20 years, many in the
industry have referred to FM Global's product testing and
certifications subsidiary, FM Approvals, for guidance when
designing, specifying and installing low-slope roof systems.
However, because of FM Global's revisions to its guidelines, some
in the industry are rethinking their reliance on FM Global and FM
Approvals and taking a different, more fundamental approach to
designing roof systems' wind resistances.
The fundamental concept of wind design as it applies to roof
systems is that the design wind-resistance (uplift-resistance)
capacity of a building's roof system should be greater than or
equal to the design wind loads that will act upon the roof system.
This relationship is expressed mathematically as: wr =
wl where wr = design wind resistance and
wl = design wind load.
In the event actual wind loads exceed a roof system's
wind-resistance capacity, the roof system may not be considered
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