ASCE 7 wind load fundamentals · Lesson 1 of 4

ASCE 7 wind load fundamentals: principles and terminology

Why the roof edge is where wind loads concentrate, what ASCE 7 is and how the building code brings it in, the chain from wind speed to zone pressure, and who does what.

You will be able to: Describe how a wind speed becomes a design pressure on edge metal, name the factors and categories that shape it, and say who decides each input.

12 min · 12 slides · 9 questions

All lessons in this module

Slide 1 of 12

Why edge metal is a wind problem

FEMA's fact sheet says public buildings with low-slope membrane roofs often fail at the edges, where wind lifts and peels metal edge flashings, copings and fascia.

IIBEC says it plainly: when edge metal fails, the roofing system cannot withstand the associated wind loads.

This module shows how the pressure on that metal is built up. It does not teach anyone to size an edge.

Sources

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
Specifying to reduce risk and improve performance of perimeter edge metal systems - IIBEC

Glossary

Basic wind speed (V): The design wind speed read from the ASCE 7 maps for a building's risk category, in mph. It is a 3-second peak gust, not a weather-report speed.
Risk category: The class, I to IV, a building falls in by the consequence of its failure. A higher category uses a longer mean recurrence interval and so a higher design wind speed.
Velocity pressure (q): The pressure of moving air, in psf, from q = 0.00256 Kz Kzt Kd Ke V squared in ASCE 7-16. Zone coefficients turn it into the pressure on a surface.
Components and cladding (C&C): The elements that take wind directly and pass it on, such as the roof covering, edge metal, fasteners and studs. They are designed with an effective wind area, unlike the main wind-force resisting system.
Mean recurrence interval: The average number of years between wind events of a given strength. ASCE 7-16 maps use 300, 700, 1,700 and 3,000 years for Risk Categories I to IV.