Because fm approvals requires a 2 1 safety factor roofs with field of roof uplift forces of 30 pounds per square foot are the maximum for 1 60 ratings and 37 5 pounds per square foot are the maximum for 1 75 ratings etc.
Fm roof uplift ratings.
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Include drawings and details of the roof cover flashing and design loads.
Fm approvals have classification ratings 1 60 1 90 or 1 120.
In the case of roofing systems fm is particularly well known for determining how roofing performs not only for fire but also for high wind.
The misconception is that these numbers correlate to wind speeds of 60 90 or 120 miles per hour.
The following information is needed to conduct a thorough review of new roof installations and re roofing projects.
These ratings actually apply to wind uplift pressure in pounds per square foot and are not directly related to.