Which diameter is used for the storm drain or rain water leader?

Which diameter is used for the storm drain or rain water leader?

• A. 6 inches
• B. 8 inches
• C. 12 inches
• D. 4 inches

Answer: (B)

The main point is why a storm drainage line from the roof, called the rain water leader, is sized large enough to carry runoff effectively. An eight-inch diameter is a common standard for this vertical discharge path because it provides ample cross-sectional area to move a large volume of water quickly during heavy rain, reducing the risk of backups or overflow. It also avoids the impracticality and higher cost of using a much larger pipe, while a four-inch or six-inch diameter could be too small to handle typical roof loads. A twelve-inch diameter would be overkill for most buildings and adds unnecessary weight and cost. In practice, eight inches strikes a balance between capacity and practicality for many storm drainage setups, though actual sizing depends on roof area, local rain intensities, and codes.

The main point is why a storm drainage line from the roof, called the rain water leader, is sized large enough to carry runoff effectively. An eight-inch diameter is a common standard for this vertical discharge path because it provides ample cross-sectional area to move a large volume of water quickly during heavy rain, reducing the risk of backups or overflow. It also avoids the impracticality and higher cost of using a much larger pipe, while a four-inch or six-inch diameter could be too small to handle typical roof loads. A twelve-inch diameter would be overkill for most buildings and adds unnecessary weight and cost. In practice, eight inches strikes a balance between capacity and practicality for many storm drainage setups, though actual sizing depends on roof area, local rain intensities, and codes.