P-1106.1 General. The size of the vertical conductors and leaders, building storm drains, building storm sewers and any horizontal branches of such drains or sewers shall be based on a the 100-year hourly rainfall rate of 4.5" per hour. indicated in Figure 1106.1 or on other rainfall rates determined from approved local weather data.
Exceptions:
1. Existing building storm drainage systems without secondary roof drainage installed in accordance with Section 1108 shall be designed based on a rainfall rate of 6" per hour.
2. The size of building storm drainage systems serving green roof systems, approved by the Philadelphia Water Department, shall be based on a rainfall rate of 3.1" per hour.
(Delete Figure 1106.1)
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