How Much Rain Runs Off A Roof

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How much rain runs off a roof.

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. Measure along the length of the house or building and along the width of the house or building in feet. How much rain water runs off your roof. Keep in mind most rain falls over 2 3 months of a year.

Step 1 determine the footprint of your structure f in square feet. Take a guess what is the volume of water that runs off a 1 000 square foot roof during a 1 rain storm. 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. 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. 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. Although this calculation is simple in principle the units can make it a headache.

Divide 100 by the number of downspouts in order to obtain the percentage of water collected from each downspout. Assuming 5 cm of rain per hour. The answer is about 623 gallons. For example on a 2 000 square foot roof you can collect 2 000 x 0 56 1 120 gallons inch of rain.

To find how much rain you can collect in an average rain year multiply this number by the average inches of rain. 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. Multiply this by the rainfall to get the volume of rain. It isn t uncommon for an area to collect up to 350mm of rain in just one month even in rural areas.

However calctool s unit menus remove this issue doing all the unit conversion for you. 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. 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.