ASCE 7 wind load fundamentals · Lesson 4 of 4

ASCE 7 wind load fundamentals: defects, verification and case study

Why roof perimeters fail first, what three hurricanes and an insurer study showed, common specification and installation defects, why an ES-1 rating covers only the assembly as tested, and a verification chain with its safety limits.

You will be able to: Recognise how edge-metal wind failures start, read what field evidence shows, and follow a verification chain from the specification to the roof without claiming a rating that was not tested.

11 min · 11 slides · 9 questions

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Slide 1 of 11

Why the perimeter fails first

IIBEC reports that nearly 60 percent of damaged roofs in post-hurricane studies were caused by failure at the perimeter.

Poor workmanship and lighter-gauge value engineering were the main causes reported.

FEMA also says low-slope membrane roofs often fail at the edges.

Sources

Specifying to reduce risk and improve performance of perimeter edge metal systems - IIBEC
Roofing on the edge (Professional Roofing, October 2018; the author is a manufacturer representative and the piece is opinion) - Professional Roofing (NRCA)
Hurricane and Flood Mitigation Handbook for Public Facilities, Fact Sheet 3.3.2 Roof Systems - Low-Slope Roofs (FEMA P-2181, March 2022) - Federal Emergency Management Agency

Glossary

Assembly-as-tested rating: An ES-1 rating applies only to the assembly as tested: its materials, thicknesses, fasteners, fastener locations and installation method. Changing any of them voids the match.
Sustained pressure: The term Drexel Metals uses for the pressure an ES-1 test assembly sustained. It is the maker's tested value, not a design demand, and the Design Engineer must apply the factor of safety.
Verification chain: The five checks from specification to roof: drawings and spec, submittal, shop, installation, and inspection after a storm, each asking whether the work matches what was tested and the design pressure.
Blanket certification: A claim that every product of a supplier is certified to ES-1. IIBEC and Professional Roofing say no edge-metal supplier holds one; ratings belong to tested assemblies.