Strapping the plies should be considered when the slope is greater than what decimal value?

• A. 0.03
• B. 0.06
• C. 0.09
• D. 0.12

Answer: (C)

When a roof is fairly steep, securing multiple plies becomes more difficult because gravity and wind can cause the layers to shift during installation. This is why strapping the plies is considered at a higher slope—to hold the plies in place and ensure proper alignment and adhesion as you apply them.

The threshold value used is nine percent (0.09). If the slope is greater than 0.09, you should evaluate whether strapping is appropriate. Slopes of 3 percent or 6 percent are gentler and usually don’t require this technique, while 12 percent represents an even steeper condition where other slope-specific procedures come into play; the recommended point to consider strapping is at 0.09.