Roof Drain Slope

Tips on calculating drain pipe slopes.

Roof drain slope.

Roof drains for flat or low slope roofs come in a few standard types. For flat roof drainage where you place your drains scuppers and the final material of the roofing is more important. Use the longest level possible for your application for the best accuracy. Increasing the angle of a flat roof will always increase the speed of water movement across the surface.

Due to the gradual low slope of this type of roof rainfall will not drain as effectively. When the bubble on a level is about 1 4 of the way past the line it is about a 1 4 slope. According to the chart for 1 8 slope per 12 of pipe for 5 000 square feet of roof area with a 6 per hour of rainfall the required pipe size is 8. To size the vertical roof drain for the same parameters 5 000 square feet of room area and 6 per hour of rain consult table 1106 2 figure 3.

The best type for the application depends on several factors such as the size and slope of the roof the desired appearance and how much regular maintenance the drain system might need. The angle is not significant enough to prevent water from pooling on the surface. Since the pitch of the roof is lower it can act as a catch all for tree limbs and other debris. Same logic with 1 8 slope 1 16 slope etc.