Wind loads and roof edge resistance · Lesson 1 of 4

Wind loads and roof edge resistance: principles and terminology

Why roof perimeters fail first, how wind pulls on a coping and a gravel stop, the vocabulary of ASCE 7-16 velocity pressure and zone coefficients, strength level versus allowable stress, and the three numbers a specifier must never confuse.

You will be able to: Define the terms of an ASCE 7 wind calculation for roof edge metal, say how wind loads a coping and a gravel stop, and tell demand, tested capacity and factor of safety apart, including who owns each.

9 min · 10 slides · 6 questions

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Slide 1 of 10

Why roof edges come first

ES-1-2022's commentary cites an FM Global study of 145 built-up roof losses in which 85, or 59 percent, happened because the roof perimeter failed.

It also reports that the Roofing Industry Committee on Weather Issues found many examples of damage that appeared to originate at failed edge details.

A loose edge component endangers people and property and starts blow-off at the roof edge.

Sources

ANSI/SPRI/FM 4435/ES-1-2022 Test Standard for Edge Systems Used with Low Slope Roofing Systems (approved November 21, 2022), including its commentary - SPRI (Single Ply Roofing Industry)

Glossary

Components and cladding: The parts of a building envelope, such as roofing and edge metal, that take wind directly. SPRI notes roofing assemblies are defined as cladding, so their wind pressures are the components and cladding pressures of ASCE 7.
Basic wind speed (V): The basic ultimate wind speed read from the ASCE 7 wind map for the building's Risk Category; ASCE 7-10 and 7-16 speeds are ultimate (strength) level.
Velocity pressure (qz): The wind pressure at height z, from qz = 0.00256 Kz Kzt Kd Ke V squared in ASCE 7-16, in pounds per square foot.
Cleat: ES-1 defines a cleat as a continuous metal strip, or angled piece, used to secure metal components; a clip is the non-continuous equivalent.
Design load: ES-1 defines it as the total load on a structural system for the most severe combination of loads and forces it is designed to sustain.
Sustained pressure: In ES-1 testing, the last one-minute load held without failure, which is recorded as the maximum load; makers such as Drexel print it as the sustained pressure of an assembly.