Wind loads and roof edge resistance · Lesson 3 of 4

Wind loads and roof edge resistance: methods and worked application

A nine-step path from code edition to a tested edge, the effect of the ASCE 7 edition on wind speed, roof and wall zone sizes, a worked velocity pressure and corner pressures, two pressure bases side by side, and how to set demand beside a published capacity.

You will be able to: Follow the specifier's sequence from code edition to tested edge, work a velocity pressure and corner pressures with stated inputs and units, and compare demand with a published capacity without calling it a pass.

11 min · 12 slides · 7 questions

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Slide 1 of 12

The specifier's sequence

Two steps serve a specifier: the engineer of record works out the design pressures for each edge condition, then you choose a tested edge that meets or exceeds them.

ES-1's commentary says copings must be tested to RE-3 and provide a strength that meets or exceeds the horizontal and vertical pressures required.

1: Confirm the code and the ASCE 7 edition the jurisdiction adopted
2: Read the basic wind speed for the Risk Category
3: Set exposure, mean roof height, Kzt, Ke and enclosure
4: Work out the velocity pressure qh
5: Apply roof and wall zones and their coefficients
6: Choose the pressure basis and the factor of safety
7: State the design pressures for each edge condition
8: Choose an edge tested by RE-2 or RE-3 to meet them
9: Install exactly as tested and keep the documentation

The specifier's sequence, drawn for this module. AFS's screening works steps 3 to 5 for ASCE 7-16 only; steps 6 and 7 belong to the engineer of record.

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)

Videos for this lesson

What this video shows: A membrane manufacturer's training video in which its technical support manager, a professional engineer, shows how to calculate wind design pressures for low-slope roofing under ASCE 7-16. It covers roof pressures, so edge metal also needs the wall-zone outward load taught here. Checked against the video's description.

Video: Low Slope Roofing Wind Design: ASCE 7-16 Calculations by SOPREMA USA, on YouTube. Chosen from the video's published description.

What this video shows: The same presenter works an ASCE 7-16 example problem for low-slope roof wind design pressures; its numbers are its own example, not this module's. Checked against the video's description.

Video: Low Slope Roofing Wind Design: ASCE 7-16 Example Problem by SOPREMA USA, on YouTube. Chosen from the video's published description.

Glossary

Least horizontal dimension: The smaller plan dimension of a building, from which ASCE 7-16 sets the wall edge zone width a: 10 percent of it or 0.4h, whichever is smaller, but not less than 4 percent of it or 3 ft.
Mean roof height (h): The building height the ASCE 7-16 low-rise method uses, up to 60 ft in this method; roof zone widths of 0.6h and 0.2h are measured from it.
Pressure basis: Whether a pressure is at strength (ultimate) level or allowable stress level, which is 0.6 times strength. AFS's screening shows strength times 2.0 and allowable stress times 2.0 side by side.
Capacity verdict: A statement that a tested assembly meets a demand. AFS's screening gives one only against a signed laboratory report for the exact assembly.