Gardening on the Edge Blog
Rainwater Catchment Formula
Wed, Jan 5 2011 10:17
| Sustainability, Solutions
| Permalink
How much rainwater can I catch off my roof?
The answer to this depends somewhat on the type or roof material and how quickly the rain is falling. The general formula for calculating how much you can catch is determined by multiplying the square footage of the roof times the annual rainfall in the area times 0.0632 gallons of rain per square feet of roof. In Asheville, we get about 47 inches of rain per year, plus or minus. Using a 2000 square foot roof:
2,000 x 47 x0.0632 = 59,000 gallons of rainwater collected a year
That’s assuming you catch 100% of the rain, which you won’t. In a light rainfall, some will evaporate before it gets to the collection point. In a heavy rainfall, some will wash over the gutters. Over hanging tree branches will stop some from hitting your roof, and. some roofing materials will absorb some of the moisture. A more realistic catchment rate would be about 80% to 90%.
The most efficient roofing materials to have for catching rainwater are stainless steel or galvanized steel which capture at about a 90% rate. At this rate, in Asheville, you would catch on the average, about 53,000 gallons of water per year off of a 2,000 square foot roof.
The answer to this depends somewhat on the type or roof material and how quickly the rain is falling. The general formula for calculating how much you can catch is determined by multiplying the square footage of the roof times the annual rainfall in the area times 0.0632 gallons of rain per square feet of roof. In Asheville, we get about 47 inches of rain per year, plus or minus. Using a 2000 square foot roof:
2,000 x 47 x0.0632 = 59,000 gallons of rainwater collected a year
That’s assuming you catch 100% of the rain, which you won’t. In a light rainfall, some will evaporate before it gets to the collection point. In a heavy rainfall, some will wash over the gutters. Over hanging tree branches will stop some from hitting your roof, and. some roofing materials will absorb some of the moisture. A more realistic catchment rate would be about 80% to 90%.
The most efficient roofing materials to have for catching rainwater are stainless steel or galvanized steel which capture at about a 90% rate. At this rate, in Asheville, you would catch on the average, about 53,000 gallons of water per year off of a 2,000 square foot roof.
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