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1. Use the following formula to determine G.P.M.:
G.P.M. = .0104 x R x A
G.P.M. = Gallons per minute
R = Rainfall intensity - inches/hour
A = Roof area - square feet
.0104 = Conversion factor - G.P.M./sq. ft. for 1" (one) inch/hr. rainfall
2. Example:
A. 4" rainfall inches/hr.
B. 100,000 sq. ft. roof area
C. G.P.M. = .0104 x 4" x 100,000 sq. ft. = 4,160 G.P.M.
3. Refer to table 2: a 4" leader [2] will handle 144 G.P.M.
4,160 G.P.M/ ÷ 144 = (28.8) 29 - 4" vertical leaders required.
Refer to Table 2: a 6" leader [2] will handle 424 G.P.M.
4, 160 G.P.M. ÷ 424 = (9.8) 10 - 6" vertical leaders required. |
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