Runoff Coefficient For Roof

On a low slope fully adhered epdm roof with slope of 1 4 per foot one could justify a coefficient of 95 to 99.

Runoff coefficient for roof.

Runoff coefficient c this coefficient allows for the quantity of water which runoff a particular type of surfacing into a drainage system and discount the quantity of water which will soak into or through the surfacing. Runoff coefficients paired rainfall p and observed runoff q obs from 21 living roofs volumetric runoff coefficient for each storm linear regression for paired p. Typical values are given below. Rational method runoff coefficients.

The formula for calculating this flow is called the maming formula. Multiply the two figures together to obtain the square footage of your roof step 2 determine the percentage of water collected from each downspout p. A runoff coefficient is a number that relates the rainfall rate and runoff rate. Measure along the length of the house or building and along the width of the house or building in feet.

One of the parameters in the rational method equation q cia is the runoff coefficient c. Tot per per tot imp impa a c a a. Rational method runoff coefficient applications. 1 predicted c v must increase or remain constant for 0 p 100 mm 2 predicted c v 1 for 0 p 100.

Why is it important. Count the number of downspouts coming from your roof. I the design rainfall intensity for a storm of specified recurrence interval and duration equal to the watershed time of concentration. The higher the value the greater the quantity of water which will need to be dealt with by the drainage system.

The rational method considers a runoff coefficient of about 0 7 0 95 for both concrete streets and roofs the most impervious and a runoff coefficient of about 0 05 0 35 for lawns areas the most pervious. The other parameters are a the area of a watershed. The runoff coefficient describes the percentage of rainfall which runs off a particular surface during a storm event. It is a larger value for areas with low infiltration and high runoff pavement steep gradient and lower for permeable well vegetated areas forest flat land.

Divide 100 by the number of downspouts in order to obtain the percentage of water collected from each downspout. Annual runoff generated roof area annual rainfall runoff coefficient 200 1000 0 9 180 000 litres or 47 520 gallons hence a storage capacity of 47 520 gallons is required to sail through the summer months with adequate water supply. There are two ways you can find the runoff coefficient. It is possible to calculate the average runoff coefficient for non homogeneous areas considering.

The runoff coefficient c is a dimensionless coefficient relating the amount of runoff to the amount of precipitation received. The american society of plumbing engineers data book suggests that initially there will be some friction along the drainage path but it will quickly go to zero. Step 1 determine the footprint of your structure f in square feet.