Vertical leaders shall be sized based on the flow rate from horizontal gutters or the maximum flow rate through roof drains. The flow rate through vertical leaders shall not exceed that specified in Table 1106.3.
TABLE 1106.3 VERTICAL LEADER SIZING
TABLE 1106.3 VERTICAL LEADER SIZING
| SIZE OF LEADER (inches) | CAPACITY (gpm) |
| 2 | 30 |
| 2 × 2 | 30 |
| 11/2 × 21/2 | 30 |
| 21/2 | 54 |
| 21/2 × 21/2 | 54 |
| 3 | 92 |
| 2 × 4 | 92 |
| 21/2×3 | 92 |
| 4 | 192 |
| 3 × 41/4 | 192 |
| 31/2 × 4 | 192 |
| 5 | 360 |
| 4 × 5 | 360 |
| 41/2 × 41/2 | 360 |
| 6 | 563 |
| 5 × 6 | 563 |
| 51/2 × 51/2 | 563 |
| 8 | 1208 |
| 6 × 8 | 1208 |
For SI: 1 inch = 25.4 mm, 1 gallon per minute = 3.785 L/m.