![]() ![]() Building owners and some specifiers and designers don't realize that the ratings apply to uplift pressures in pounds per square foot (psf), not wind speeds.įurthermore, the roofing designer or specifier sometimes assumes if there is a design wind speed requirement of 90 mph, then the roof system must have a 1-90 rating, which is not always true - at least not for the reason they think (maybe for tall buildings, or if other factors exist). One common misconception is the belief that FM Approvals' windstorm classification ratings such as 1-60, 1-90 or 1-120 correlate to wind speeds of 60, 90 or 120 miles per hour (mph). ![]() Neither FM Approvals nor FM Global are building code-making bodies, but FM-approved roofing systems are often specified, so it's important that specifiers and designers understand FM Approval's role and the wind ratings. Common Misconceptions FM Approvals' work has driven the evolution of many types of roofing systems and certainly has played a big role in the development of the high-performance fastening systems we use today.
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