Roof Pitch For Water Runoff

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.

Roof pitch for water runoff. It is an essential element to ensure water drains properly off of your roof. The primary reason roof pitch exists in the first place is to redirect water. A 4 12 slope is enough to accommodate water runoff but is not suitable for regions that are affected by heavy snowfall. The roof pitch would be described as a 6 12 pitch.

A 4 12 roof pitch indicates the roof rises 4 inches in height for every 12 inches as measured. Water will flow as long as the drainage angle is greater than zero. The pitch of your roof also helps determine the type of materials that can be used on your roofing system. This forms an angle of 18 5 between the horizontal section and the roof and creates a gentle incline that is seen as a midpoint between a low pitch and medium pitch roof.

If it is a large roof it is recommended to have drains placed at multiple locations within the area of the roof. The slope of a roof or pitch is determined by how many inches the roof rises over 1 foot or 12 inches. However not just any pitch above zero is suitable for all kinds of drainage. Roofs require slope for adequate drainage and even so called flat roofs must have some incline.

Every roof needs drainage. Divide 100 by the number of downspouts in order to obtain the percentage of water collected from each downspout. This means that the rise of the slope goes up or down 8 inches for every 12 inches. 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.

Convert the percentage to a decimal by dividing the percentage by 100. 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. Step 2 multiply the area of your roof by the amount of rainfall you wish to calculate for.

An example for a steep sloped roof is 8 12. The main aim of having a drain or drainage is to redirect runoff away from the roof to other designated places. Count the number of downspouts coming from your roof.