How Much Rain Runs Off A Roof

Take a guess what is the volume of water that runs off a 1 000 square foot roof during a 1 rain storm.

How much rain runs off a roof.

Although this calculation is simple in principle the units can make it a headache. 500 000 square cm multiplied by 5 cm is 2 500 000 cubic cm of rain. Count the number of downspouts coming from your roof. If your average rainfall was 25 inches year your annual collection potential is 1 120 x 25 28 000 gallons year.

It isn t uncommon for an area to collect up to 350mm of rain in just one month even in rural areas. Assuming 5 cm of rain per hour. Show comments you may like. 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. However calctool s unit menus remove this issue doing all the unit conversion for you. 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.

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. You may be as astonished as we were to learn how much water runs off a roof in a rain storm. The answer is about 623 gallons. Step 1 determine the footprint of your structure f in square feet.

An average suburban roof of 200m 2 with such a rain fall can potentially harvest 100 000l of rainwater 200m 2 500mm 100 000l. 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. For example on a 2 000 square foot roof you can collect 2 000 x 0 56 1 120 gallons inch of rain. Multiply this by the rainfall to get the volume of rain.

Keep in mind most rain falls over 2 3 months of a year. 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. 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.