Where asphalt is used, rock is not practical on roofs with a slope greater than:

Where asphalt is used, rock is not practical on roofs with a slope greater than:

• A. 2:12
• B. 3:12
• C. 4:12
• D. 5:12

Answer: (B)

Rock ballast is used to hold down roofing membranes on low-slope roofs, but its practicality drops as the roof gets steeper. Loose rock on a roof can slide or be blown off by wind, and workers have limited ability to safely place or maintain ballast on steeper surfaces. Because of these safety and performance concerns, ballast becomes impractical once the slope passes about 3:12. On slopes steeper than that, asphalt-based systems are used instead, since they’re designed to be secured without relying on loose ballast. Slopes around 2:12 or less are still within the range where ballast can be used, while slopes of 4:12 or 5:12 are too steep for ballast and require different roofing methods.

Rock ballast is used to hold down roofing membranes on low-slope roofs, but its practicality drops as the roof gets steeper. Loose rock on a roof can slide or be blown off by wind, and workers have limited ability to safely place or maintain ballast on steeper surfaces. Because of these safety and performance concerns, ballast becomes impractical once the slope passes about 3:12. On slopes steeper than that, asphalt-based systems are used instead, since they’re designed to be secured without relying on loose ballast. Slopes around 2:12 or less are still within the range where ballast can be used, while slopes of 4:12 or 5:12 are too steep for ballast and require different roofing methods.