Roof Pitch For Water Runoff

Step 2 multiply the area of your roof by the amount of rainfall you wish to calculate for.

Roof pitch for water runoff.

The primary reason roof pitch exists in the first place is to redirect water. Divide 100 by the number of downspouts in order to obtain the percentage of water collected from each downspout. If it is a large roof it is recommended to have drains placed at multiple locations within the area of the roof. A 4 12 roof pitch indicates the roof rises 4 inches in height for every 12 inches as measured.

The roof pitch would be described as a 6 12 pitch. Roofs require slope for adequate drainage and even so called flat roofs must have some incline. The slope of a roof or pitch is determined by how many inches the roof rises over 1 foot or 12 inches. A 4 12 slope is enough to accommodate water runoff but is not suitable for regions that are affected by heavy snowfall.

Water will flow as long as the drainage angle is greater than zero. Count the number of downspouts coming from your roof. I have been advised that a roof with a pitch of 8 12 or greater is too steep for a metal roof and the water run off has such a speed that in a heavy rain the water pressure will tear the gutters off the house. This can be located at the edge or in the middle of the roof.

The area we are calculating here is the same as if your roof were flat. An example for a steep sloped roof is 8 12. Determine the percentage of water collected from each downspout p. How water sheds off a roof depends on how much rain falls in that location and how quickly it needs to drain.

To put it in perspective the angle of this slope would be around 30 degrees. This means that the rise of the slope goes up or down 8 inches for every 12 inches. Convert the percentage to a decimal by dividing the percentage by 100. The pitch of your roof also helps determine the type of materials that can be used on your roofing system.

Even though most roofs are pitched at an angle the only part that will affect the rain runoff is the actual area underneath your roof. Every roof needs drainage. The main aim of having a drain or drainage is to redirect runoff away from the roof to other designated places.