How Much Rain Runs Off A Roof

Although this calculation is simple in principle the units can make it a headache.

How much rain runs off a roof. The basic calculation is a x r 231 g where a is the area of your roof in square feet r is the amount of rain in inches and g is the amount of runoff in gallons. Assuming 5 cm of rain per hour. However calctool s unit menus remove this issue doing all the unit conversion for you. Multiply this by the rainfall to get the volume of rain.

Just multiple the square footage of roof space you have available x 0 6 gallons per square foot per inch of rain and you can see how much water you can collect from each inch of rain that falls. Take a guess what is the volume of water that runs off a 1 000 square foot roof during a 1 rain storm. Measure along the length of the house or building and along the width of the house or building in feet. You may be as astonished as we were to learn how much water runs off a roof in a rain storm.

Count the number of downspouts coming from your roof. For example if you have a roof that measures 50 square metres that equals 500 000 square cm 1 square metre 10 000 square cm. An average suburban roof of 200m 2 with such a rain fall can potentially harvest 100 000l of rainwater 200m 2 500mm 100 000l. The answer is about 623 gallons.

Here you can easily find how much rainwater you can collect from you roof how much you need to remove from a courtyard or how much runoff you can expect from an area of land. If your average rainfall was 25 inches year your annual collection potential is 1 120 x 25 28 000 gallons year. How much rain water runs off your roof. While this is a normal aspect of roofing and gutters water that pours off of a roof and drenches an area like a door stoop or porch not only makes these spots slippery but water falling.

To find how much rain you can collect in an average rain year multiply this number by the average inches of rain. Divide 100 by the number of downspouts in order to obtain the percentage of water collected from each downspout. 500 000 square cm multiplied by 5 cm is 2 500 000 cubic cm of rain. For example on a 2 000 square foot roof you can collect 2 000 x 0 56 1 120 gallons inch of rain.

Show comments you may like. So if you have 2 500 square feet of roof available for water catchment and a single inch of rain falls one day we see that. Keep in mind most rain falls over 2 3 months of a year.