In the ballast depth calculation example, what is the height above grade used to compute ballast depth along the fascia?

• A. 10 feet
• B. 60 feet
• C. 40 feet
• D. 20 feet

Answer: (C)

The height above grade used is forty feet. Ballast depth along the fascia is tied to how tall the edge of the roof is above grade because wind and gravity loads acting on that edge grow with vertical exposure. Using forty feet as the height captures the exposure at the fascia and determines how much ballast is needed to resist uplift and lateral movement. If a different height were used, the calculated ballast depth would change to reflect the different loading at that edge.