Stormwater Conductors

Capacities of roof drains

Capacities of horizontal sloped and vertical stormwater and rainwater leaders:

Imperial Units

Pipe Size NPS
(in)
Vertical Roof Drains
(gpm)
Horizontal Sloped Pipe (gpm)
Slope 1/8
(in/ft)
Slope 1/4
(in/ft)
Slope 1/2
(in/ft)
3 90 35 50 70
4 190 80 110 157
5 360 140 200 280
6 560 225 315 450
8 1200 480 680 950
10 860 1220 1728

Metric Units

Pipe Size DN
(mm)
Vertical Roof Drains
(l/s)
Horizontal Sloped Pipe (l/s)
Slope 1
(cm/m)
Slope 2.1
(cm/m)
Slope 4.2
(cm/m)
80 5.8 2.1 3.0 4.3
100 12 4.9 6.9 9.9
125 23 8.8 12 18
150 35 14 20 28
200 76 30 43 60
250 54 77 109

Related Topics

  • Water Systems - Hot and cold water service systems - design properties, capacities, sizing and more

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